Astronomy Picture of the Day Search Results for "moon"

APOD: 2025 March 14 - Moon Pi and Mountain Shadow
Explanation: What phase of the Moon is 3.14 radians from the Sun? The Full Moon, of course. Even though the Moon might look full for several days, the Moon is truly at its full phase when it is Pi radians (aka 180 degrees) from the Sun in ecliptic longitude. That's opposite the Sun in planet Earth's sky. Rising as the Sun set on March 9, 2020, only an hour or so after the moment of its full phase, this orange tinted and slightly flattened Moon still looked full. It was photographed opposite the setting Sun from Teide National Park on the Canary Island of Tenerife. Also opposite the setting Sun, seen from near the Teide volcano peak about 3,500 meters above sea level, is the mountain's rising triangular shadow extending into Earth's dense atmosphere. Below the distant ridge line on the left are the white telescope domes of Teide Observatory. Today, March 14 2025, the moon is Pi radians from the Sun at exactly 06:55 UTC. That's about three minutes before the midpoint of the March Full Moon's total lunar eclipse.

APOD: 2025 January 18 - Full Moon, Full Mars
Explanation: On January 13 a Full Moon and a Full Mars were close, both bright and opposite the Sun in planet Earth's sky. In fact Mars was occulted, passing behind the Moon, when viewed from some locations in North America and northwest Africa. As seen from Richmond, Virginia, USA, this composite image sequence follows the evening lunar occultation before, during, and after the much anticipated celestial spectacle. The telescopic time series is constructed from an exposure made every two minutes while tracking the Moon over the hours encompassing the event. As a result, the Red Planet's trajectory seems to follow a gently curved path due to the Moon's slightly different rate of apparent motion. The next lunar occultation of bright planet Mars will be on February 9 when the moon is in a waxing gibbous phase. Lunar occultations are only ever visible from a fraction of the Earth's surface, though. The February 9 occultation of Mars will be seen from parts of Russia, China, eastern Canada, Greenland and other (mostly northern) locations, but a close conjunction of a bright Moon with Mars will be more widely visible from planet Earth.

APOD: 2025 January 15 – Wolf Moon Engulfs Mars
Explanation: Does the Moon ever engulf Mars? Yes, but only in the sense that it moves in front, which happens on rare occasions. This happened just yesterday, though, as seen from some locations in North America and western Africa. This occultation was notable not only because the Moon was a fully lit Wolf Moon, but because Mars was near its largest and brightest, moving to opposition -- the closest to the Earth in its orbit -- only tomorrow. The engulfing, more formally called an occultation, typically lasts about an hour. The featured image was taken from near Chicago, Illinois, USA just as Earth's largest satellite was angularly moving away from the much more distant red planet. Our Moon occasionally moves in front of all of the Solar System's planets. Given the temporary alignment of orbital planes, the next time our Moon eclipses Mars will be a relatively soon February 9.

APOD: 2024 December 20 - The Long Night Moon
Explanation: On the night of December 15, the Full Moon was bright. Known to some as the Cold Moon or the Long Night Moon, it was the closest Full Moon to the northern winter solstice and the last Full Moon of 2024. This Full Moon was also at a major lunar standstill. A major lunar standstill is an extreme in the monthly north-south range of moonrise and moonset caused by the precession of the Moon's orbit over an 18.6 year cycle. As a result, the full lunar phase was near the Moon's northernmost moonrise (and moonset) along the horizon. December's Full Moon is rising in this stacked image, a composite of exposures recording the range of brightness visible to the eye on the northern winter night. Along with a colorful lunar corona and aircraft contrail this Long Night Moon shines in a cold sky above the rugged, snowy peaks of the Italian Dolomites.

APOD: 2024 September 20 - A Hazy Harvest Moon
Explanation: For northern hemisphere dwellers, September's Full Moon was the Harvest Moon. On September 17/18 the sunlit lunar nearside passed into shadow, just grazing Earth's umbra, the planet's dark, central shadow cone, in a partial lunar eclipse. Over the two and a half hours before dawn a camera fixed to a tripod was used to record this series of exposures as the eclipsed Harvest Moon set behind Spiš Castle in the hazy morning sky over eastern Slovakia. Famed in festival, story, and song, Harvest Moon is just the traditional name of the full moon nearest the autumnal equinox. According to lore the name is a fitting one. Despite the diminishing daylight hours as the growing season drew to a close, farmers could harvest crops by the light of a full moon shining on from dusk to dawn. This September's Harvest Moon was also known to some as a supermoon, a term becoming a traditional name for a full moon near perigee.

APOD: 2024 September 15 – Find the Man in the Moon
Explanation: Have you ever seen the Man in the Moon? This common question plays on the ability of humans to see pareidolia -- imagining familiar icons where they don't actually exist. The textured surface of Earth's full Moon is home to numerous identifications of iconic objects, not only in modern western culture but in world folklore throughout history. Examples, typically dependent on the Moon's perceived orientation, include the Woman in the Moon and the Rabbit in the Moon. One facial outline commonly identified as the Man in the Moon starts by imagining the two dark circular areas -- lunar maria -- here just above the Moon's center, to be the eyes. Surprisingly, there actually is a man in this Moon image -- a close look will reveal a real person -- with a telescope -- silhouetted against the Moon. This well-planned image was taken in 2016 in Cadalso de los Vidrios in Madrid, Spain.

APOD: 2024 September 3 – Quarter Moon and Sister Stars
Explanation: Nine days ago, two quite different sky icons were imaged rising together. Specifically, Earth's Moon shared the eastern sky with the sister stars of the Pleiades cluster, as viewed from Alberta, Canada. Astronomical images of the well-known Pleiades often show the star cluster's alluring blue reflection nebulas, but here they are washed-out by the orange moonrise sky. The half-lit Moon, known as a quarter moon, is overexposed, although the outline of the dim lunar night side can be seen by illuminating earthshine, light first reflected from the Earth. The featured image is a composite of eight successive exposures with brightnesses adjusted to match what the human eye would see. The Moon passes nearly -- or directly -- in front of the Pleaides once a month.

APOD: 2024 August 27 – Moon Eclipses Saturn
Explanation: What if Saturn disappeared? Sometimes, it does. It doesn't really go away, though, it just disappears from view when our Moon moves in front. Such a Saturnian eclipse, more formally called an occultation, was visible along a long swath of Earth -- from Peru, across the Atlantic Ocean, to Italy -- only a few days ago. The featured color image is a digital fusion of the clearest images captured during the event and rebalanced for color and relative brightness between the relatively dim Saturn and the comparatively bright Moon. Saturn and the comparative bright Moon. The exposures were all taken from Breda, Catalonia, Spain, just before occultation. Eclipses of Saturn by our Moon will occur each month for the rest of this year. Each time, though, the fleeting event will be visible only to those with clear skies -- and the right location on Earth.

APOD: 2024 July 27 - Saturn at the Moon's Edge
Explanation: Saturn now rises before midnight in planet Earth's sky. On July 24, the naked-eye planet was in close conjunction, close on the sky, to a waning gibbous Moon. But from some locations on planet Earth the ringed gas giant was occulted, disappearing behind the Moon for about an hour from skies over parts of Asia and Africa. Because the Moon and bright planets wander through the sky near the ecliptic plane, such occultation events are not uncommon, but they can be dramatic. In this telescopic view from Nanjing, Jiangsu, China, Saturn is caught moments before its disappearance behind the lunar disk. The snapshot gives the illusion that Saturn hangs just above Glushko crater, a 43 kilometer diameter, young, ray crater near the Moon's western edge. Of course, the Moon is 400 thousand kilometers away, compared to Saturn's distance of 1.4 billion kilometers.

APOD: 2024 July 24 – Exaggerated Moon
Explanation: Our Moon doesn't really have craters this big. Earth's Moon, Luna, also doesn't naturally show this spikey texture, and its colors are more subtle. But this digital creation is based on reality. The featured image is a digital composite of a good Moon image and surface height data taken from NASA's Lunar Orbiter Laser Altimeter (LOLA) mission -- and then exaggerated for educational understanding. The digital enhancements, for example, accentuate lunar highlands and show more clearly craters that illustrate the tremendous bombardment our Moon has been through during its 4.6-billion-year history. The dark areas, called maria, have fewer craters and were once seas of molten lava. Additionally, the image colors, although based on the moon's real composition, are changed and exaggerated. Here, a blue hue indicates a region that is iron rich, while orange indicates a slight excess of aluminum. Although the Moon has shown the same side to the Earth for billions of years, modern technology is allowing humanity to learn much more about it -- and how it affects the Earth.

APOD: 2024 June 29 - A Solstice Moon
Explanation: Rising opposite the setting Sun, June's Full Moon occurred within about 28 hours of the solstice. The Moon stays close to the Sun's path along the ecliptic plane and so while the solstice Sun climbed high in daytime skies, June's Full Moon remained low that night as seen from northern latitudes. In fact, the Full Moon hugs the horizon in this June 21 rooftop night sky view from Bursa, Turkey, constructed from exposures made every 10 minutes between moonrise and moonset. In 2024 the Moon also reached a major lunar standstill, an extreme in the monthly north-south range of moonrise and moonset caused by the precession of the Moon's orbit over an 18.6 year cycle. As a result, this June solstice Full Moon was at its southernmost moonrise and moonset along the horizon.

APOD: 2024 June 20 - Sandy and the Moon Halo
Explanation: Last April's Full Moon shines through high clouds near the horizon, casting shadows in this garden-at-night skyscape. Along with canine sentinel Sandy watching the garden gate, the wide-angle snapshot also captured the bright Moon's 22 degree ice halo. But June's bright Full Moon will cast shadows too. This month, the Moon's exact full phase occurs at 01:08 UTC June 22. That's a mere 28 hours or so after today's June solstice (at 20:51 UTC June 20), the moment when the Sun reaches its maximum northern declination. Known to some as a Strawberry Moon, June's Full Moon is at its southernmost declination, and of course will create its own 22 degree halos in hazy night skies.

APOD: 2024 June 2 – Rotating Moon from LRO
Explanation: No one, presently, sees the Moon rotate like this. That's because the Earth's moon is tidally locked to the Earth, showing us only one side. Given modern digital technology, however, combined with many detailed images returned by the Lunar Reconnaissance Orbiter (LRO), a high resolution virtual Moon rotation movie has been composed. The featured time-lapse video starts with the standard Earth view of the Moon. Quickly, though, Mare Orientale, a large crater with a dark center that is difficult to see from the Earth, rotates into view just below the equator. From an entire lunar month condensed into 24 seconds, the video clearly shows that the Earth side of the Moon contains an abundance of dark lunar maria, while the lunar far side is dominated by bright lunar highlands. Currently, over 32 new missions to the Moon are under active development from multiple countries and companies, including NASA's Artemis program which aims to land people on the Moon again within the next few years.

APOD: 2024 March 14 - Moon Pi and Mountain Shadow
Explanation: What phase of the Moon is 3.14 radians from the Sun? The Full Moon, of course. Even though the Moon might look full for several days, the Moon is truly at its full phase when it is Pi radians (aka 180 degrees) from the Sun in ecliptic longitude. That's opposite the Sun in planet Earth's sky. Rising as the Sun set on March 9, 2020, only an hour or so after the moment of its full phase, this orange tinted and slightly flattened Moon still looked full. It was photographed opposite the setting Sun from Teide National Park on the Canary Island of Tenerife. Also opposite the setting Sun, seen from near the Teide volcano peak about 3,500 meters above sea level, is the mountain's rising triangular shadow extending into Earth's dense atmosphere. Below the distant ridge line on the left are the white telescope domes of Teide Observatory. Again Pi radians from the Sun, on March 25 the Full Moon will dim slightly as it glides through Earth's outer shadow in a penumbral lunar eclipse.

APOD: 2024 February 26 – Martian Moon Eclipses Martian Moon
Explanation: What if there were two moons in the sky -- and they eclipsed each other? This happens on Mars. The featured video shows a version of this unusual eclipse from space. Pictured are the two moons of Mars: the larger Phobos, which orbits closer to the red planet, and the smaller Deimos, which orbits further out. The sequence was captured last year by the ESA’s Mars Express, a robotic spacecraft that itself orbits Mars. A similar eclipse is visible from the Martian surface, although very rarely. From the surface, though, the closer moon Phobos would appear to pass in front of farther moon Deimos. Most oddly, Phobos orbits Mars so close that it appears to move backwards when compared to Earth's Moon from Earth, rising in west and setting in the east. Phobos, the closer moon, orbits so close and so fast that it passes nearly overhead about three times a day.

APOD: 2024 February 13 – A January Wolf Moon
Explanation: Did you see the full moon last month? During every month, on average, a full moon occurs in the skies over planet Earth. This is because the Moon takes a month to complete another orbit around our home planet, goes through all of its phases, and once again has its entire Earth-facing half lit by reflected sunlight. Many indigenous cultures give each full moon a name, and this past full moon's names include the Ice Moon, the Stay at Home Moon, and the Quiet Moon. Occurring in January on the modern western calendar, several cultures have also named the most recent full moon the Wolf Moon, in honor of the famous howling animal. Featured here above the Italian Alps mountains, this past Wolf Moon was captured in combined long and short exposure images. The image is striking because, to some, the surrounding clouds appear as a wolf's mouth ready to swallow the Wolf Moon, while others see the Moon as a wolf's eye.

APOD: 2024 February 11 – Rocket Plume Shadow Points to the Moon
Explanation: Why would the shadow of a rocket's launch plume point toward the Moon? In early 2001 during a launch of the space shuttle Atlantis, the Sun, Earth, Moon, and rocket were all properly aligned for this photogenic coincidence. First, for the space shuttle's plume to cast a long shadow, the time of day must be either near sunrise or sunset. Only then will the shadow be its longest and extend all the way to the horizon. Finally, during a Full Moon, the Sun and Moon are on opposite sides of the sky. Just after sunset, for example, the Sun is slightly below the horizon, and, in the other direction, the Moon is slightly above the horizon. Therefore, as Atlantis blasted off, just after sunset, its shadow projected away from the Sun toward the opposite horizon, where the Full Moon happened to be.

APOD: 2024 January 30 – SLIM Lands on the Moon
Explanation: New landers are on the Moon. Nearly two weeks ago, Japan's Smart Lander for Investigating Moon (SLIM) released two rovers as it descended, before its main lander touched down itself. The larger of the two rovers can hop like a frog, while the smaller rover is about the size of a baseball and can move after pulling itself apart like a transformer. The main lander, nicknamed Moon Sniper, is seen in the featured image taken by the smaller rover. Inspection of the image shows that Moon Sniper's thrusters are facing up, meaning that the lander is upside down from its descent configuration and on its side from its intended landing configuration. One result is that Moon Sniper's solar panels are not in the expected orientation, so that powering the lander had to be curtailed and adapted. SLIM's lander has already succeeded as a technology demonstration, its main mission, but was not designed to withstand the lunar night -- which starts tomorrow.

APOD: 2024 January 27 - Full Observatory Moon
Explanation: A popular name for January's full moon in the northern hemisphere is the Full Wolf Moon. As the new year's first full moon, it rises over Las Campanas Observatory in this dramatic Earth-and-moonscape. Peering from the foreground like astronomical eyes are the observatory's twin 6.5 meter diameter Magellan telescopes. The snapshot was captured with telephoto lens across rugged terrain in the Chilean Atacama Desert, taken at a distance of about 9 miles from the observatory and about 240,000 miles from the lunar surface. Of course the first full moon of the lunar new year, known to some as the Full Snow Moon, will rise on February 24.

APOD: 2024 January 24 – Earth and Moon from Beyond
Explanation: What do the Earth and Moon look like from beyond the Moon? Although frequently photographed together, the familiar duo was captured with this unusual perspective in late 2022 by the robotic Orion spacecraft of NASA's Artemis I mission as it looped around Earth's most massive satellite and looked back toward its home world. Since our Earth is about four times the diameter of the Moon, the satellite’s seemingly large size was caused by the capsule being closer to the smaller body. Artemis II, the next launch in NASA’s Artemis series, is currently scheduled to take people around the Moon in 2025, while Artemis III is planned to return humans to lunar surface in late 2026. Last week, JAXA's robotic SLIM spacecraft, launched from Japan, landed on the Moon and released two hopping rovers.

APOD: 2024 January 2 – Rocket Transits Rippling Moon
Explanation: Can a rocket make the Moon ripple? No, but it can make a background moon appear wavy. The rocket, in this case, was a SpaceX Falcon Heavy that blasted off from NASA's Kennedy Space Center last week. In the featured launch picture, the rocket's exhaust plume glows beyond its projection onto the distant, rising, and nearly full moon. Oddly, the Moon's lower edge shows unusual drip-like ripples. The Moon itself, far in the distance, was really unchanged. The physical cause of these apparent ripples was pockets of relatively hot or rarefied air deflecting moonlight less strongly than pockets of relatively cool or compressed air: refraction. Although the shot was planned, the timing of the launch had to be just right for the rocket to be transiting the Moon during this single exposure.

APOD: 2023 December 3 – Moon Setting Behind Teide Volcano
Explanation: These people are not in danger. What is coming down from the left is just the Moon, far in the distance. Luna appears so large here because she is being photographed through a telescopic lens. What is moving is mostly the Earth, whose spin causes the Moon to slowly disappear behind Mount Teide, a volcano in the Canary Islands off the northwest coast of Africa. The people pictured are 16 kilometers away and many are facing the camera because they are watching the Sun rise behind the photographer. It is not a coincidence that a full moon rises just when the Sun sets because the Sun is always on the opposite side of the sky from a full moon. The featured video was made in 2018 during the full Milk Moon. The video is not time-lapse -- this was really how fast the Moon was setting.

APOD: 2023 November 12 – Gibbous Moon beyond Swedish Mountain
Explanation: This is a gibbous Moon. More Earthlings are familiar with a full moon, when the entire face of Luna is lit by the Sun, and a crescent moon, when only a sliver of the Moon's face is lit. When more than half of the Moon is illuminated, though, but still short of full illumination, the phase is called gibbous. Rarely seen in television and movies, gibbous moons are quite common in the actual night sky. The featured image was taken in Jämtland, Sweden near the end of 2018 October. That gibbous moon turned, in a few days, into a crescent moon, and then a new moon, then back to a crescent, and a few days past that, back to gibbous. Setting up to capture a picturesque gibbous moonscape, the photographer was quite surprised to find an airplane, surely well in the foreground, appearing to fly past it.

APOD: 2023 September 30 - A Harvest Moon over Tuscany
Explanation: For northern hemisphere dwellers, September's Full Moon was the Harvest Moon. Reflecting warm hues at sunset, it rises behind cypress trees huddled on a hill top in Tuscany, Italy in this telephoto view from September 28. Famed in festival, story, and song, Harvest Moon is just the traditional name of the full moon nearest the autumnal equinox. According to lore the name is a fitting one. Despite the diminishing daylight hours as the growing season drew to a close, farmers could harvest crops by the light of a full moon shining on from dusk to dawn. This Harvest Moon was also known to some as a supermoon, a term becoming a traditional name for a full moon near perigee. It was the fourth and final supermoon for 2023.

APOD: 2023 September 17 – Moon Mountains Magnified during Ring of Fire Eclipse
Explanation: What are those dark streaks in this composite image of a solar eclipse? They are reversed shadows of mountains at the edge of the Moon. The center image, captured from Xiamen, China, has the Moon's center directly in front of the Sun's center. The Moon, though, was too far from the Earth to completely block the entire Sun. Light that streamed around the edges of the Moon is called a ring of fire. Images at each end of the sequence show sunlight that streamed through lunar valleys. As the Moon moved further in front of the Sun, left to right, only the higher peaks on the Moon's perimeter could block sunlight. Therefore, the dark streaks are projected, distorted, reversed, and magnified shadows of mountains at the Moon's edge. Bright areas are called Baily's Beads. Only people in a narrow swath across Earth's Eastern Hemisphere were able to view this full annular solar eclipse in 2020. Next month, though, a narrow swath crossing both North and South America will be exposed to the next annular solar eclipse. And next April, a total solar eclipse will be visible across North America.

APOD: 2023 August 8 – Moon Meets Jupiter
Explanation: What's that below the Moon? Jupiter -- and its largest moons. Many skygazers across planet Earth enjoyed the close conjunction of Earth's Moon passing nearly in front of Jupiter in mid-June. The featured image is a single exposure of the event taken from Morón de la Frontera, Spain. The sunlit lunar crescent on the left is overexposed, while the Moon's night side, on the right, is only faintly illuminated by Earthshine. Lined up diagonally below the Moon, left to right, are Jupiter's bright Galilean satellites: Callisto, Ganymede, Io (hard to see as it is very near to Jupiter), and Europa. In fact, Callisto, Ganymede, and Io are larger than Earth's Moon, while Europa is only slightly smaller. NASA's robotic spacecraft Juno is currently orbiting Jupiter and made a close pass near Io only a week ago. If you look up in the night sky tonight, you will again see two of the brightest objects angularly close together -- because tonight is another Moon-Jupiter conjunction.

APOD: 2023 May 24 – Observatory Aligned with Moon Occulting Jupiter
Explanation: Sometimes we witness the Moon moving directly in front of -- called occulting -- one of the planets in our Solar System. Earlier this month that planet was Jupiter. Captured here was the moment when Jupiter re-appeared from behind the surface of our Moon. The Moon was in its third quarter, two days before the dark New Moon. Now, our Moon is continuously half lit by the Sun, but when in its third quarter, relatively little of that half can be seen from the Earth. Pictured, the Moon itself was aligned behind the famous Lick Observatory in California, USA, on the summit of Mount Hamilton. Coincidentally, Lick enabled the discovery of a moon of Jupiter: Amalthea, the last visually detected moon of Jupiter after Galileo's observations.

APOD: 2023 April 30 – Saturn's Moon Helene in Color
Explanation: Although its colors may be subtle, Saturn's moon Helene is an enigma in any light. The moon was imaged in unprecedented detail in 2012 as the robotic Cassini spacecraft orbiting Saturn swooped to within a single Earth diameter of the diminutive moon. Although conventional craters and hills appear, the above image also shows terrain that appears unusually smooth and streaked. Planetary astronomers are inspecting these detailed images of Helene to glean clues about the origin and evolution of the 30-km across floating iceberg. Helene is also unusual because it circles Saturn just ahead of the large moon Dione, making it one of only four known Saturnian moons to occupy a gravitational dimple known as a stable Lagrange point.

APOD: 2023 February 28 – Crescent Moon Beyond Greek Temple
Explanation: Why is a thin crescent moon never seen far from a horizon? Because the only geometry that gives a thin crescent lunar phase occurs when the Moon appears close to the Sun in the sky. The crescent is not caused by the shadow of the Earth, but by seeing only a small part of the Moon directly illuminated by the Sun. Moreover, the thickest part of the crescent always occurs in the direction of the Sun. In the evening, a thin crescent Moon will set shortly after the Sun and not be seen for the rest of the night. Alternatively, in the morning, a crescent Moon will rise shortly before the Sun after not being seen for most of the night. Pictured two weeks ago, a crescent moon was captured near the horizon, just before sunrise, far behind remnants of the ancient Temple of Poseidon in Greece.

APOD: 2023 January 16 – Moon Enhanced
Explanation: Our Moon doesn't really look like this. Earth's Moon, Luna, doesn't naturally show this rich texture, and its colors are more subtle. But this digital creation is based on reality. The featured image is a composite of multiple images and enhanced to bring up real surface features. The enhancements, for example, show more clearly craters that illustrate the tremendous bombardment our Moon has been through during its 4.6-billion-year history. The dark areas, called maria, have fewer craters and were once seas of molten lava. Additionally, the image colors, although based on the moon's real composition, are changed and exaggerated. Here, a blue hue indicates a region that is iron rich, while orange indicates a slight excess of aluminum. Although the Moon has shown the same side to the Earth for billions of years, modern technology is allowing humanity to learn much more about it -- and how it affects the Earth.

APOD: 2023 January 6 - Moon O'Clock 2022
Explanation: The first Full Moon of 2023 is in the sky tonight opposite the Sun at 23:08 UTC. Big and beautiful, the Moon at its brightest phase should be easy to spot. Still, for quick reference images captured near the times of all the full moons of 2022 are aranged in this dedicated astro-imaging project from Sri Lanka, planet Earth. The day, month, and a traditional popular name for 2022's twelve full moons are given in the chart. The apparent size of each full moon depends on how close the full lunar phase is to perigee or apogee, the closest or farthest point in the Moon's elliptical orbit. Like the 2022 Wolf Moon at the 1 o'clock position, tonight's Full Moon occurs within about two days of apogee. But unlike in 2022, the year 2023 will have 13 full moons that won't all fit nicely on the twelve hour clock.

APOD: 2022 December 15 - Full Moon, Full Mars
Explanation: On December 8 a full Moon and a full Mars were close, both bright and opposite the Sun in planet Earth's sky. In fact Mars was occulted, passing behind the Moon when viewed from some locations across Europe and North America. Seen from the city of Kosice in eastern Slovakia, the lunar occultation of Mars happened just before sunrise. The tantalizing spectacle was recorded in this telescopic timelapse sequence of exposures. It took about an hour for the Red Planet to disappear behind the lunar disk and then reappear as a warm-hued full Moon, the last full Moon of 2022, sank toward the western horizon. The next lunar occultation of bright planet Mars will be in the new year on January 3, when the Moon is in a waxing gibbous phase. Lunar occultations are only ever visible from a fraction of the Earth's surface, though. The January 3 occultation of Mars will be visible from parts of the South Atlantic, southern Africa, and the Indian Ocean.

APOD: 2022 October 14 - The Falcon and the Hunter's Moon
Explanation: The Full Moon of October 9th was the second Full Moon after the northern hemisphere autumnal equinox, traditionally called the Hunter's Moon. According to lore, the name is a fitting one because this Full Moon lights the night during a time for hunting in preparation for the coming winter months. In this snapshot, a nearly full Hunter's Moon was captured just after sunset on October 8, rising in skies over Florida's Space Coast. Rising from planet Earth a Falcon 9 rocket pierces the bright lunar disk from the photographer's vantage point. Ripples and fringes along the edge of the lunar disk appear as supersonic shock waves generated by the rocket's passage change the atmosphere's index of refraction.

APOD: 2022 September 15 - Harvest Moon over Sicily
Explanation: For northern hemisphere dwellers, September's Full Moon was the Harvest Moon. Reflecting warm hues at sunset it rises over the historic town of Castiglione di Sicilia in this telephoto view from September 9. Famed in festival, story, and song Harvest Moon is just the traditional name of the full moon nearest the autumnal equinox. According to lore the name is a fitting one. Despite the diminishing daylight hours as the growing season drew to a close, farmers could harvest crops by the light of a full moon shining on from dusk to dawn.

APOD: 2022 July 25 - Find the New Moon
Explanation: Can you find the Moon? This usually simple task can be quite difficult. Even though the Moon is above your horizon half of the time, its phase can be anything from crescent to full. The featured image was taken in late May from Sant Martí d'Empúries, Spain, over the Mediterranean Sea in the early morning. One reason you can't find this moon is because it is very near to its new phase, when very little of the half illuminated by the Sun is visible to the Earth. Another reason is because this moon is near the horizon and so seen through a long path of Earth's atmosphere -- a path which dims the already faint crescent. Any crescent moon is only visible near the direction the Sun, and so only locatable near sunrise or sunset. The Moon runs through all of its phases in a month (moon-th), and this month the thinnest sliver of a crescent -- a new moon -- will occur in three days.

APOD: 2022 June 12 - Find the Man in the Moon
Explanation: Have you ever seen the Man in the Moon? This common question plays on the ability of humans to see pareidolia -- imagining familiar icons where they don't actually exist. The textured surface of Earth's full Moon is home to numerous identifications of iconic objects, not only in modern western culture but in world folklore throughout history. Examples, typically dependent on the Moon's perceived orientation, include the Woman in the Moon and the Rabbit in the Moon. One facial outline commonly identified as the Man in the Moon starts by imagining the two dark circular areas -- lunar maria -- here just above the Moon's center, to be the eyes. Surprisingly, there actually is a man in this Moon image -- a close look will reveal a real person -- with a telescope -- silhouetted against the Moon. This featured well-planned image was taken in 2016 in Cadalso de los Vidrios in Madrid, Spain. Do you have a favorite object that you see in the Moon?

APOD: 2022 May 15 - Colors of the Moon
Explanation: What color is the Moon? It depends on the night. Outside of the Earth's atmosphere, the dark Moon, which shines by reflected sunlight, appears a magnificently brown-tinged gray. Viewed from inside the Earth's atmosphere, though, the moon can appear quite different. The featured image highlights a collection of apparent colors of the full moon documented by one astrophotographer over 10 years from different locations across Italy. A red or yellow colored moon usually indicates a moon seen near the horizon. There, some of the blue light has been scattered away by a long path through the Earth's atmosphere, sometimes laden with fine dust. A blue-colored moon is more rare and can indicate a moon seen through an atmosphere carrying larger dust particles. What created the purple moon is unclear -- it may be a combination of several effects. The last image captures the total lunar eclipse of 2018 July -- where the moon, in Earth's shadow, appeared a faint red -- due to light refracted through air around the Earth. Today there is not only another full moon but a total lunar eclipse visible to observers in North and South America -- an occurrence that may lead to some unexpected lunar colorings.

APOD: 2022 February 28 - Direct Projection: The Moon in My Hands
Explanation: You don't have to look through a telescope to know where it's pointing. Allowing the telescope to project its image onto a large surface can be useful because it dilutes the intense brightness of very bright sources. Such dilution is useful for looking at the Sun, for example during a solar eclipse. In the featured single-exposure image, though, it is a too-bright full moon that is projected. This February full moon occurred two weeks ago and is called the Snow Moon by some northern cultures. The projecting instrument is the main 62-centimeter telescope at the Saint-Véran Observatory high in the French Alps. Seeing a full moon directly is easier because it is not too bright, although you won't see this level of detail. Your next chance will occur on March 17.

APOD: 2022 February 15 - Terminator Moon
Explanation: What's different about this Moon? It's the terminators. In the featured image, you can't directly see any terminator -- the line that divides the light of day from the dark of night. That's because the image is a digital composite of 29 near-terminator lunar strips. Terminator regions show the longest and most prominent shadows -- shadows which, by their contrast and length, allow a flat photograph to appear three-dimensional. The original images and data were taken near the Moon by NASA's Lunar Reconnaissance Orbiter. Many of the Moon's craters stand out because of the shadows they all cast to the right. The image shows in graphic detail that the darker regions known as maria are not just darker than the rest of the Moon -- they are flatter.

APOD: 2022 February 1 - Moon Phases 2022
Explanation: What will the Moon phase be on your birthday this year? It is hard to predict because the Moon's appearance changes nightly. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The featured video animates images and altitude data taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter to show all 12 lunations that appear this year, 2022 -- as seen from Earth's northern (southern) hemisphere. A single lunation describes one full cycle of our Moon, including all of its phases. A full lunation takes about 29.5 days, just under a month (moon-th). As each lunation progresses, sunlight reflects from the Moon at different angles, and so illuminates different features differently. During all of this, of course, the Moon always keeps the same face toward the Earth. What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.

APOD: 2022 January 1 - The Full Moon of 2021
Explanation: Every Full Moon of 2021 shines in this year-spanning astrophoto project, a composite portrait of the familiar lunar nearside at each brightest lunar phase. Arranged by moonth, the year progresses in stripes beginning at the top. Taken with the same camera and lens the stripes are from Full Moon images all combined at the same pixel scale. The stripes still look mismatched, but they show that the Full Moon's angular size changes throughout the year depending on its distance from Kolkata, India, planet Earth. The calendar month, a full moon name, distance in kilometers, and angular size is indicated for each stripe. Angular size is given in minutes of arc corresponding to 1/60th of a degree. The largest Full Moon is near a perigee or closest approach in May. The smallest is near an apogee, the most distant Full Moon in December. Of course the full moons of May and November also slid into Earth's shadow during 2021's two lunar eclipses.

APOD: 2021 December 1 - A Blue Banded Blood Moon
Explanation: What causes a blue band to cross the Moon during a lunar eclipse? The blue band is real but usually quite hard to see. The featured HDR image of last week's lunar eclipse, however -- taken from Yancheng, China -- has been digitally processed to equalize the Moon's brightness and exaggerate the colors. The gray color of the bottom right is the Moon's natural color, directly illuminated by sunlight. The upper left part of the Moon is not directly lit by the Sun since it is being eclipsed -- it in the Earth's shadow. It is faintly lit, though, by sunlight that has passed deep through Earth's atmosphere. This part of the Moon is red -- and called a blood Moon -- for the same reason that Earth's sunsets are red: because air scatters away more blue light than red. The unusual blue band is different -- its color is created by sunlight that has passed high through Earth's atmosphere, where red light is better absorbed by ozone than blue. A total eclipse of the Sun will occur this weekend but, unfortunately, totality be visible only near the Earth's South Pole.

APOD: 2021 October 18 - Earthshine Moon over Sicily
Explanation: Why can we see the entire face of this Moon? When the Moon is in a crescent phase, only part of it appears directly illuminated by the Sun. The answer is earthshine, also known as earthlight and the da Vinci glow. The reason is that the rest of the Earth-facing Moon is slightly illuminated by sunlight first reflected from the Earth. Since the Earth appears near full phase from the Moon -- when the Moon appears as a slight crescent from the Earth -- earthshine is then near its brightest. Featured here in combined, consecutively-taken, HDR images taken earlier this month, a rising earthshine Moon was captured passing slowly near the planet Venus, the brightest spot near the image center. Just above Venus is the star Dschubba (catalogued as Delta Scorpii), while the red star on the far left is Antares. The celestial show is visible through scenic cloud decks. In the foreground are the lights from Palazzolo Acreide, a city with ancient historical roots in Sicily, Italy.

APOD: 2021 October 10 - Full Moon Silhouettes
Explanation: Have you ever watched the Moon rise? The slow rise of a nearly full moon over a clear horizon can be an impressive sight. One impressive moonrise was imaged in early 2013 over Mount Victoria Lookout in Wellington, New Zealand. With detailed planning, an industrious astrophotographer placed a camera about two kilometers away and pointed it across the lookout to where the Moon would surely soon be making its nightly debut. The featured single shot sequence is unedited and shown in real time -- it is not a time lapse. People on Mount Victoria Lookout can be seen in silhouette themselves admiring the dawn of Earth's largest satellite. Seeing a moonrise yourself is not difficult: it happens every day, although only half the time at night. Each day the Moon rises about fifty minutes later than the previous day, with a full moon always rising at sunset. This Saturday, October 16, is International Observe the Moon Night, where you observe a first-quarter Moon along with other lunar enthusiasts.

APOD: 2021 September 23 - Harvest Moon Trail
Explanation: Famed in festival, story, and song the best known full moon is the Harvest Moon. For northern hemisphere dwellers that's a traditional name of the full moon nearest the September equinox. Seen from Saunderstown, Rhode Island, planet Earth, this Harvest Moon left a broad streak of warm hues as it rose through a twilight sky over the Newport Bridge. On September 20 its trail was captured in a single 22 minute exposure using a dense filter and a digital camera. Only two days later the September equinox marked a change of season and the beginning of autumn in the north. In fact, recognizing a season as the time between solstice and equinox, this Harvest Moon was the fourth full moon of the season, coming just before the astronomical end of northern summer.

APOD: 2021 August 31 - A Blue Moon in Exaggerated Colors
Explanation: The Moon is normally seen in subtle shades of grey or gold. But small, measurable color differences have been greatly exaggerated to make this telescopic, multicolored, moonscape captured during the Moon's full phase. The different colors are recognized to correspond to real differences in the chemical makeup of the lunar surface. Blue hues reveal titanium rich areas while orange and purple colors show regions relatively poor in titanium and iron. The familiar Sea of Tranquility, or Mare Tranquillitatis, is the blue area toward the upper right. White lines radiate across the orange-hued southern lunar highlands from 85-kilometer wide ray-crater Tycho at bottom right. The full moon that occurred earlier this month could be counted as a seasonal blue moon because it was, unusually, the third of four full moons to occur during northern summer (and hence southern winter). The featured 272-image composite demonstrates that the full Moon is always blue, but usually not blue enough in hue to ooh.

APOD: 2021 August 26 - A Blue Hour Full Moon
Explanation: Nature photographers and other fans of planet Earth always look forward to the blue hour. That's the transition in twilight, just before sunrise or after sunset, when the Sun is below the horizon but land and sky are still suffused with a beautiful blue light. After sunset on August 21, this blue hour snapshot captured the nearly full Moon as it rose opposite the Sun, above the rugged Italian Alps from Cortina d'Ampezzo, Italy. Sharing bluish hues with the sky, the rocky pyramid of Monte Antelao, also known as the King of the Dolomites, is the region's prominent alpine peak. The moonlight is yellow, but even so this full Moon was known to some as a seasonal Blue Moon. That's because by one definition the third full Moon of a season with four full moons in it is called a Blue Moon. Recognizing a season as the time between a solstice and an equinox, this season's fourth full Moon will be rising in the blue hour of September 20, just before September's equinox.

APOD: 2021 July 11 - Find the Moon
Explanation: Where's the Moon? Somewhere in this image, the Earth's Moon is hiding. The entire Moon is visible, in its completely full phase, in plain sight. Even the photographer's keen eye couldn't find it even though he knew exactly where to look -- only the long exposure of his camera picked it up -- barely. Although by now you might be congratulating yourself on finding it, why was it so difficult to see? For one reason, this photograph was taken during a total lunar eclipse, when the Earth's shadow made the Moon much dimmer than a normal full Moon. For another, the image, taken in Colorado, USA, was captured just before sunrise. With the Moon on the exact opposite side of the sky from the Sun, this meant that the Sun was just below the horizon, but still slightly illuminating the sky. Last, as the Moon was only about two degrees above the horizon, the large volume of air between the camera and the horizon scattered a lot of light away from the background Moon. Twelve minutes after this image was acquired in 2012, the Sun peeked over the horizon and the Moon set.

APOD: 2021 June 9 - A Total Lunar Eclipse Corona
Explanation: This moon appears multiply strange. This moon was a full moon, specifically called a Flower Moon at this time of the year. But that didn't make it strange -- full moons occur once a month (moon-th). This moon was a supermoon, meaning that it reached its full phase near its closest approach to the Earth in its slightly elliptical orbit. Somewhat strange, a supermoon appears a bit larger and brighter than the average full moon -- and enables it to be called a Super Flower Moon.  This moon was undergoing a total lunar eclipse. An eclipsed moon can look quite strange, being dark, unevenly lit, and, frequently, red -- sometimes called blood red. Therefore, this moon could be called a Super Flower Blood Moon. This moon was seen through thin clouds. These clouds created a faint corona around the moon, making it look not only strange, but colorful. This moon was imaged so deeply that the heart of the Milky Way galaxy, far in the background, was visible to its lower right. This moon, this shadow, this galaxy and these colors were all captured last month near Cassilis, NSW, Australia -- with a single shot. (Merged later with two lower shots that better capture the Milky Way.)

APOD: 2021 May 25 - The Moon During a Total Lunar Eclipse
Explanation: How does the Moon's appearance change during a total lunar eclipse? The featured time-lapse video was digitally processed to keep the Moon bright and centered during the 5-hour eclipse of 2018 January 31. At first the full moon is visible because only a full moon can undergo a lunar eclipse. Stars move by in the background because the Moon orbits the Earth during the eclipse. The circular shadow of the Earth is then seen moving across the Moon. The light blue hue of the shadow's edge is related to why Earth's sky is blue, while the deep red hue of the shadow's center is related to why the Sun appears red when near the horizon. Tomorrow, people living from southeast Asia, across the Pacific, to the southwest Americas may get to see a Blood Supermoon Total Lunar Eclipse. Here the term blood refers to the (likely) red color of the fully eclipsed Moon, while the term supermoon indicates the Moon's slightly high angular size -- due to being relatively close to the Earth in its slightly elliptical orbit.

APOD: 2021 April 30 - Pink and the Perigee Moon
Explanation: On April 25 a nearly full moon rose just before sunset. Welcomed in a clear blue sky and framed by cherry blossoms, its familiar face was captured in this snapshot from Leith, Edinburgh, Scotland. Known to some as a Pink Moon, April's full lunar phase occurred with the moon near perigee. That's the closest point in its not-quite-circular orbit around planet Earth, making this Pink Moon one of the closest and brightest full moons of the year. If you missed it, don't worry. Your next chance to see a full perigee moon will be on May 26. Known to some as a Flower Moon, May's full moon will actually be closer to you than April's by about 98 miles (158 kilometers), or about 0.04% the distance from the Earth to the Moon at perigee.

APOD: 2021 February 3 - Found on the Moon: Candidate for Oldest Known Earth Rock
Explanation: Was the oldest known rock on Earth found on the Moon? Quite possibly. The story opens with the Apollo 14 lunar mission. Lunar sample 14321, a large rock found in Cone crater by astronaut Alan Shepard, when analyzed back on Earth, was found to have a fragment that was a much better match to Earth rocks than other Moon rocks. Even more surprising, that rock section has recently been dated back 4 billion years, making it older, to within measurement uncertainty, than any rock ever found on Earth. A leading hypothesis now holds that an ancient comet or asteroid impact launched Earth rocks into the Solar System, some of which fell back to the Moon, became mixed with heated lunar soil and other rocks, cooled, and re-fragmented. The video features an internal X-ray scan of 14321 showing multiple sections with markedly different chemistries. Moon rocks will continue to be studied to learn a more complete history of the Moon, the Earth, and the early Solar System. Friday marks the 50th Anniversary of the Apollo 14 landing on the Moon.

APOD: 2021 January 11 - Moon Phases in 2021
Explanation: What will the Moon phase be on your birthday this year? It is hard to predict because the Moon's appearance changes nightly. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The featured video animates images taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter to show all 12 lunations that appear this year, 2021. A single lunation describes one full cycle of our Moon, including all of its phases. A full lunation takes about 29.5 days, just under a month (moon-th). As each lunation progresses, sunlight reflects from the Moon at different angles, and so illuminates different features differently. During all of this, of course, the Moon always keeps the same face toward the Earth. What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.

APOD: 2020 November 11 - Colors of the Moon
Explanation: What color is the Moon? It depends on the night. Outside of the Earth's atmosphere, the dark Moon, which shines by reflected sunlight, appears a magnificently brown-tinged gray. Viewed from inside the Earth's atmosphere, though, the moon can appear quite different. The featured image highlights a collection of apparent colors of the full moon documented by one astrophotographer over 10 years from different locations across Italy. A red or yellow colored moon usually indicates a moon seen near the horizon. There, some of the blue light has been scattered away by a long path through the Earth's atmosphere, sometimes laden with fine dust. A blue-colored moon is more rare and can indicate a moon seen through an atmosphere carrying larger dust particles. What created the purple moon is unclear -- it may be a combination of several effects. The last image captures the total lunar eclipse of 2018 July -- where the moon, in Earth's shadow, appeared a faint red -- due to light refracted through air around the Earth. The next full moon will occur at the end of this month (moon-th) and is known in some cultures as the Beaver Moon.

APOD: 2020 October 2 - Biking to the Moon
Explanation: As you watched October's first Full Moon rise last night, the Full Moon closest to the northern autumnal equinox, you were probably asking yourself, "How long would it take to bike to the Moon?" Sure, Apollo 11 astronauts made the trip in 1969, from launch to Moon landing, in about 103 hours or 4.3 days. But the Moon is 400,000 kilometers away. This year, the top bike riders in planet Earth's well-known Tour de France race covered almost 3,500 kilometers in 21 stages after about 87 hours on the road. That gives an average speed of about 40 kilometers per hour and a lunar cycling travel time of 10,000 hours, a little over 416 days. While this bike rider's destination isn't clear, his journey did begin around moonrise on September 27 near Cleeve Hill, Bishops Cleeve, Cheltenham, UK.

APOD: 2020 September 26 - Moon Pairs and the Synodic Month
Explanation: Observe the Moon each night and its visible sunlit portion will gradually change. In phases progressing from New Moon to Full Moon to New Moon again, a lunar cycle or synodic month is completed in about 29.5 days. They look full, but top left to bottom right these panels do show the range of lunar phases for a complete synodic month during August 2019 from Ragusa, Sicily, Italy, planet Earth. For this lunar cycle project the panels organize images of the lunar phases in pairs. Each individual image is paired with another image separated by about 15 days, or approximately half a synodic month. As a result the opposite sunlit portions complete the lunar disk and the shadow line at the boundary of lunar night and day, the terminator, steadily marches across the Moon's familiar nearside. For extra credit, what lunar phase would you pair with the Moon tonight?

APOD: 2020 September 14 - Corn Moon Rising
Explanation: A rising moon can be a dramatic sight. A rising Full Corn Moon was captured early this month in time-lapse with a telephoto lens from nearly 30 kilometers away -- making Earth's ascending half-degree companion appear unusually impressive. The image was captured from Portugal, although much of the foreground -- including lights from the village of Puebla de Guzmán -- is in Spain. A Full Corn Moon is the name attributed to a full moon at this time of year by cultures of some northern indigenous peoples of the Americas, as it coincides with the ripening of corn. Note that the Moon does not appear larger when it is nearer the horizon -- its seemingly larger size there is only an illusion. The next full moon -- occurring at the beginning of next month -- will be known as the Full Harvest Moon as it occurs nearest in time to the northern autumnal equinox and the northern field harvests.

APOD: 2020 July 19 - Rotating Moon from LRO
Explanation: No one, presently, sees the Moon rotate like this. That's because the Earth's moon is tidally locked to the Earth, showing us only one side. Given modern digital technology, however, combined with many detailed images returned by the Lunar Reconnaissance Orbiter (LRO), a high resolution virtual Moon rotation movie has been composed. The featured time-lapse video starts with the standard Earth view of the Moon. Quickly, though, Mare Orientale, a large crater with a dark center that is difficult to see from the Earth, rotates into view just below the equator. From an entire lunar month condensed into 24 seconds, the video clearly shows that the Earth side of the Moon contains an abundance of dark lunar maria, while the lunar far side is dominated by bright lunar highlands. Currently, over 19 new missions to the Moon are under active development from eight different countries, most of which have expected launch dates in the next three years.

APOD: 2020 June 22 - Moon Mountains Magnified during Ring of Fire Eclipse
Explanation: What are those dark streaks in this composite image of yesterday's solar eclipse? They are reversed shadows of mountains at the edge of the Moon. The center image, captured from Xiamen, China, has the Moon's center directly in front of the Sun's center. The Moon, though, was too far from the Earth to completely block the entire Sun. Light that streamed around all of the edges of the Moon is called a ring of fire. Images at each end of the sequence show sunlight that streamed through lunar valleys. As the Moon moved further in front of the Sun, left to right, only the higher peaks on the Moon's perimeter could block sunlight. Therefore, the dark streaks are projected, distorted, reversed, and magnified shadows of mountains at the Moon's edge. Bright areas are called Baily's Beads. Only a narrow swath across Earth's Eastern Hemisphere was able to see yesterday's full annular solar eclipse. Next June, though, a narrow swath across Earth's Northern Hemisphere will be able to see the next annular solar eclipse. A total solar eclipse will be visible at the bottom of the world near the end of this year.

APOD: 2020 June 21 - Moon Occults Venus
Explanation: It may look like Earthrise, but it's actually Venus-set. Just after sunrise two days ago, both the Moon and Venus also rose. But then the Moon overtook Venus. In the featured image sequence centered on the Moon, Venus is shown increasingly angularly close to the Moon. In the famous Earthrise image taken just over 50 years ago, the Earth was captured rising over the edge of the Moon, as seen from the Apollo 8 crew orbiting the Moon. This similar Venus-set image was taken from Earth, of course, specifically Estonia. Venus shows only a thin crescent because last week it passed nearly in front of the Sun, as seen from Earth. The Moon shows only a thin crescent because it will soon be passing directly in front of the Sun, as seen from Earth. Today, in fact, two days after this image was taken, the Moon will create a solar eclipse, with a thin swath across the Earth treated to an annular solar eclipse.

APOD: 2020 May 7 - Analemma of the Moon
Explanation: An analemma is that figure-8 curve you get when you mark the position of the Sun at the same time each day for one year. But the trick to imaging an analemma of the Moon is to wait bit longer. On average the Moon returns to the same position in the sky about 50 minutes and 29 seconds later each day. So photograph the Moon 50 minutes 29 seconds later on successive days. Over one lunation or lunar month it will trace out an analemma-like curve as the Moon's actual position wanders due to its tilted and elliptical orbit. To create this composite image of a lunar analemma, astronomer Gyorgy Soponyai chose a lunar month from March 26 to April 18 with a good stretch of weather and a site close to home near Mogyorod, Hungary. Crescent lunar phases too thin and faint to capture around the New Moon are missing though. Facing southwest, the lights of Budapest are in the distance of the base image taken on March 27.

APOD: 2020 April 10 - Full Moon of Spring
Explanation: From home this Full Moon looked bright. Around our fair planet it rose as the Sun set on April 7/8, the first Full Moon after the vernal equinox and the start of northern hemisphere spring. April's full lunar phase was also near perigee, the closest point in the Moon's elliptical orbit. In fact, it was nearer perigee than any other Full Moon of 2020 making it the brightest Full Moon of the year. To create the visual experience a range of exposures was blended to capture the emerging foreground foliage and bright lunar disk. The hopefull image of spring was recorded from a home garden in skies over Chongqing, China.

APOD: 2020 March 22 - Moon Setting Behind Teide Volcano
Explanation: These people are not in danger. What is coming down from the left is just the Moon, far in the distance. Luna appears so large here because she is being photographed through a telescopic lens. What is moving is mostly the Earth, whose spin causes the Moon to slowly disappear behind Mount Teide, a volcano in the Canary Islands off the northwest coast of Africa. The people pictured are 16 kilometers away and many are facing the camera because they are watching the Sun rise behind the photographer. It is not a coincidence that a full moon rises just when the Sun sets because the Sun is always on the opposite side of the sky from a full moon. The featured video was made two years ago during the full Milk Moon. The video is not time-lapse -- this was really how fast the Moon was setting.

APOD: 2020 March 3 - Apollo 13 Views of the Moon
Explanation: What if the only way to get back to Earth was to go around the far side of the Moon? Such was the dilemma of the Apollo 13 Crew in 1970 as they tried to return home in their unexpectedly damaged spacecraft. With the Moon in the middle, their perilous journey substituted spectacular views of the lunar farside for radio contact with NASA's Mission Control. These views have now been digitally recreated from detailed images of the Moon taken by the robotic Lunar Reconnaissance Orbiter. The featured video starts by showing Earth disappear behind a dark lunar limb, while eight minutes later the Sun rises around the opposite side of the Moon and begins to illuminate the Moon's unusual and spectacularly cratered surface. Radio contact was only re-established several minutes after that, as a crescent Earth rose into view. With the gravity of the Moon and the advice of many industrious NASA engineers and scientists, a few days later Apollo 13 opened its parachutes over the Pacific Ocean and landed safely back on Earth.

APOD: 2020 February 24 - Moon Corona, Halo, and Arcs over Manitoba
Explanation: Yes, but could you get to work on time if the Moon looked like this? As the photographer was preparing to drive to work, refraction, reflection, and even diffraction of moonlight from millions of falling ice crystals turned the familiar icon of our Moon into a menagerie of other-worldly halos and arcs. The featured scene was captured with three combined exposures two weeks ago on a cold winter morning in Manitoba, Canada. The colorful rings are a corona caused by quantum diffraction by small drops of water or ice near the direction of the Moon. Outside of that, a 22-degree halo was created by moonlight refracting through six-sided cylindrical ice crystals. To the sides are moon dogs, caused by light refracting through thin, flat, six-sided ice platelets as they flittered toward the ground. Visible at the top and bottom of the 22-degree halo are upper and lower tangent arcs, created by moonlight refracting through nearly horizontal hexagonal ice cylinders. A few minutes later, from a field just off the road to work, the halo and arcs had disappeared, the sky had returned to normal -- with the exception of a single faint moon dog.

APOD: 2019 September 13 - A Harvest Moon
Explanation: Famed in festival, story, and song the best known full moon is the Harvest Moon. For northern hemisphere dwellers that's a traditional name of the full moon nearest the September equinox. In most North America time zones this year's Harvest Moon will officially rise on Friday, September 13. In fact the same Harvest Moon will rise on September 14 for much of the planet though. Of course the Moon will look almost full in the surrounding days. Regardless of your time zone the Harvest Moon, like any other full moon, will rise just opposite the setting Sun. Near the horizon, the Moon Illusion might make it appear bigger and brighter to you but this Harvest Moon will be near lunar apogee. That's the farthest point in its orbit, making it the most distant, and so the smallest, full moon of the year. On August 15 a wheat field harvested in south central France made this a harvest moon scene too, the full moon shining on with beautiful iridescent clouds at sunset.

APOD: 2019 August 14 - Saturn Behind the Moon
Explanation: What's that next to the Moon? Saturn. In its monthly trip around the Earth -- and hence Earth's sky -- our Moon passed nearly in front of Sun-orbiting Saturn earlier this week. Actually the Moon passed directly in front of Saturn from the viewpoints of a wide swath of Earth's Southern Hemisphere. The featured image from Sydney, Australia captured the pair a few minutes before the eclipse. The image was a single shot lasting only 1/500th of a second, later processed to better highlight both the Moon and Saturn. Since Saturn is nearly opposite the Sun, it can be seen nearly the entire night, starting at sunset, toward the south and east. The gibbous Moon was also nearly opposite the Sun, and so also visible nearly the entire night -- it will be full tomorrow night. The Moon will occult Saturn again during every lap it makes around the Earth this year.

APOD: 2019 July 22 - HDR: Earths Circular Shadow on the Moon
Explanation: What could create such a large circular shadow on the Moon? The Earth. Last week's full Moon -- the Buck Moon -- was so full that it fell almost exactly in a line with the Sun and the Earth. When that happens the Earth casts its shadow onto the Moon. The circularity of the Earth's shadow on the Moon was commented on by Aristotle and so has been noticed since at least the 4th century BC. What's new is humanity's ability to record this shadow with such high dynamic range (HDR). The featured HDR composite of last week's partial lunar eclipse combines 15 images and include an exposure as short as 1/400th of a second -- so as not to overexpose the brightest part -- and an exposure that lasted five seconds -- to bring up the dimmest part. This dimmest part -- inside Earth's umbra -- is not completely dark because some light is refracted through the Earth's atmosphere onto the Moon. A total lunar eclipse will occur next in 2021 May.

APOD: 2019 July 16 - Apollo 11 Launches Humans to the Moon
Explanation: Everybody saw the Moon. Nobody had ever been there. Humans across planet Earth watched in awe 50 years ago today as a powerful Saturn V rocket attempted to launch humans -- to the Moon. Some in space flight guessed that the machinery was so complex, that so many things had to go right for it to work, that Apollo 11 would end up being another useful dress rehearsal for a later successful Moon-landing mission. But to the Moon they went. The featured video starts by showing astronauts Aldrin, Armstrong, and Collins making their way to the waiting rocket. As the large and mighty Saturn V launched, crowds watched from Cape Canaveral in Florida, USA and on television around the world. The events that unfolded over the next few days, including a dramatic moon walk 50 years ago this Saturday, will forever be remembered as a milestone in human history and an unrivaled demonstration of human ingenuity. This week, many places around the world are planning celebrations of the 50th anniversary of the first humans landing on the Moon.

APOD: 2019 June 18 - Strawberry Moon over the Temple of Poseidon
Explanation: Did you see the full moon last night? If not, tonight's nearly full moon should be almost as good. Because full moons are opposite the Sun, they are visible in the sky when the Sun is not -- which should be nearly all night long tonight, clouds permitting. One nickname for June's full moon is the Strawberry Moon, named for when wild strawberries start to ripen in parts of Earth's northern hemisphere. Different cultures around the globe give this full moon different names, though, including Honey Moon and Rose Moon. In the foreground of this featured image, taken yesterday in Cape Sounion, Greece, is the 2,400 year-old Temple of Poseidon. Next month will the 50th anniversary of the time humans first landed on the Moon.

APOD: 2019 February 12 - Plane Crossing a Crescent Moon
Explanation: No, this is not a good way to get to the Moon. What is pictured is a chance superposition of an airplane and the Moon. The contrail would normally appear white, but the large volume of air toward the setting Sun preferentially knocks away blue light, giving the reflected trail a bright red hue. Far in the distance, well behind the plane, is a crescent Moon, also slightly reddened. Captured a month ago above Valais, Switzerland, the featured image was taken so soon after sunset that planes in the sky were still in sunlight, as were their contrails. Within minutes, unfortunately, the impromptu sky show ended. The plane crossed the Moon and moved out of sight. The Moon set. The contrail became unilluminated and then dispersed.

APOD: 2019 February 6 - Moon and Venus Appulse over a Tree
Explanation: What's that bright spot near the Moon? Venus. About a week ago, Earth's Moon appeared unusually close to the distant planet Venus, an angular coincidence known as an appulse. Similar to a conjunction, which is a coordinate term, an appulse refers more generally to when two celestial objects appear close together. This Moon and Venus appulse -- once as close as 0.05 degrees -- was captured rising during the early morning behind Koko crater on the island of O'ahu in Hawaii, USA. The Moon was in a crescent phase with its lower left reflecting direct sunlight, while the rest of the Moon is seen because of Earthshine, sunlight first reflected from the Earth. Some leaves and branches of a foreground kiawe tree are seen in silhouette in front of the bright crescent, while others, in front of a darker background, appear white because of forward scattering. Appulses involving the Moon typically occur several times a year: for example the Moon is expected to pass within 0.20 degrees of distant Saturn on March 1.

APOD: 2018 November 19 - Gibbous Moon beyond Swedish Mountain
Explanation: This is a gibbous Moon. More Earthlings are familiar with a full moon, when the entire face of Luna is lit by the Sun, and a crescent moon, when only a sliver of the Moon's face is lit. When more than half of the Moon is illuminated, though, but still short of full illumination, the phase is called gibbous. Rarely seen in television and movies, gibbous moons are quite common in the actual night sky. The featured image was taken in Jämtland, Sweden near the end of last month. That gibbous moon turned, in a few days, into a crescent moon, and then a new moon, then back to a crescent, and a few days ago back to gibbous. And this same gibbous moon is visible again tonight, leading up to the Full Beaver Moon that occurs Friday night. Setting up to capture a picturesque gibbous moonscape, the photographer was quite surprised to find an airplane, surely well in the foreground, appearing to fly past it.

APOD: 2018 November 10 - The Old Moon in the Young Moon's Arms
Explanation: Tonight the Moon is young again, but this stunning image of a young Moon near the western horizon was taken just after sunset on October 10. On the lunar disk Earthshine, earthlight reflected from the Moon's night side, is embraced by the slim, sunlit crescent just over 2 days old. Along the horizon fading colors of twilight silhouette the radio telescope dish antennas of the Very Large Array, New Mexico, planet Earth. The view from the Moon would be stunning, too. When the Moon appears in Earth's sky as a slender crescent, a dazzlingly bright, nearly full Earth would be seen from the lunar surface. A description of earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci.

APOD: 2018 September 4 - Moon behind Lava Fountain
Explanation: What's happened to the Moon? Nothing, but something has happened to the image of the Moon. The heat from a volcanic lava fountain in the foreground has warmed and made turbulent the air nearby, causing passing light to refract differently than usual. The result is a lava plume that appears to be melting the Moon. The featured picture was taken as the full Sturgeon Moon was setting behind Mt. Etna as it erupted in Italy about one week ago. The picture is actually a composite of two images, one taken right after the other, with the same camera and lens. The first image was a quick exposure to capture details of the setting Moon, while the second exposure, taken after the Moon set a few minutes later, was longer so as to capture details of the faint lava jets. From our Earth, we can only see the Sun, Moon, planets, and stars as they appear through the distortion of the Earth's atmosphere. This distortion can not only change the images of familiar orbs into unusual shapes, it can --unexpectedly at times -- delay sunset and moonset by several minutes.

APOD: 2018 July 17 - Moon and Venus over Cannon Beach
Explanation: What's that spot next to the Moon? Venus. Two days ago, the crescent Moon slowly drifted past Venus, appearing within just one degree at its closest. This conjunction, though, was just one of several photographic adventures for our Moon this month (moon-th), because, for one, a partial solar eclipse occurred just a few days before, on July 12. Currently, the Moon appears to be brightening, as seen from the Earth, as the fraction of its face illuminated by the Sun continues to increase. In a few days, the Moon will appear more than half full, and therefore be in its gibbous phase. Next week the face of the Moon that always faces the Earth will become, as viewed from the Earth, completely illuminated by the Sun. Even this full phase will bring an adventure, though, as a total eclipse of this Thunder Moon will occur on July 27. Don't worry about our Luna getting tired, though, because she'll be new again next month (moon-th) -- August 11 to be exact -- just as she causes another partial eclipse of the Sun. Pictured, Venus and the Moon were captured from Cannon Beach above a rock formation off the Oregon (USA) coast known as the Needles. About an hour after this image was taken, the spin of the Earth caused both Venus and the Moon to set.

APOD: 2018 June 30 - The East 96th Street Moon
Explanation: A very full Moon rose over Manhattan's Upper Eastside on June 28, known to some as the Strawberry Moon. Near the horizon, the warm yellow lunar disk was a bit ruffled and dimmed by a long sight-line through dense, hazy atmosphere. Still it fit well with traffic and lights along East 96th street in this urban astroimage. The telephoto shot was (safely) taken from elevated ground looking east-southeast from Central Park, planet Earth. Of course, the East 96th street moon was the closest Full Moon to this year's northern summer solstice.

APOD: 2018 June 24 - Rocket Plume Shadow Points to the Moon
Explanation: Why would the shadow of a space shuttle launch plume point toward the Moon? In early 2001 during a launch of Atlantis, the Sun, Earth, Moon, and rocket were all properly aligned for this photogenic coincidence. First, for the space shuttle's plume to cast a long shadow, the time of day must be either near sunrise or sunset. Only then will the shadow be its longest and extend all the way to the horizon. Finally, during a Full Moon, the Sun and Moon are on opposite sides of the sky. Just after sunset, for example, the Sun is slightly below the horizon, and, in the other direction, the Moon is slightly above the horizon. Therefore, as Atlantis blasted off, just after sunset, its shadow projected away from the Sun toward the opposite horizon, where the Full Moon happened to be.

APOD: 2018 June 4 - Moon Setting Behind Teide Volcano
Explanation: These people are not in danger. What is coming down from the left is just the Moon, far in the distance. Luna appears so large here because she is being photographed through a telescopic lens. What is moving is mostly the Earth, whose spin causes the Moon to slowly disappear behind Mount Teide, a volcano in the Canary Islands off the northwest coast of Africa. The people pictured are 16 kilometers away and many are facing the camera because they are watching the Sun rise behind the photographer. It is not a coincidence that a full moon rises just when the Sun sets because the Sun is always on the opposite side of the sky from a full moon. The featured video was made last week during the full Milk Moon. The video is not time-lapse -- this was really how fast the Moon was setting.

APOD: 2018 March 28 - Blue Moon Tree
Explanation: Does an alignment like this occur only once in a blue moon? No, although it was during a blue moon that this single-shot image was taken. During a full moon that happened to be the second of the month -- the situation that defines a blue moon -- the photographer created the juxtaposition in late January by quickly moving around to find just the right spot to get the background Moon superposed behind the arc of a foreground tree. Unfortunately, in this case, there seemed no other way than getting bogged down in mud and resting the camera on a barbed-wire fence. The arc in the oak tree was previously created by hungry cows in Knight's Ferry, California, USA. Quirky Moon-tree juxtapositions like this can be created during any full moon though, given enough planning and time. Another opportunity will arise this weekend, coincidently during another blue moon. Then, the second blue moon in 2018 will occur, meaning that for the second month this year, two full moons will appear during a single month (moon-th). Double blue-moon years are relatively rare, with the last occurring in 1999, and the next in 2037.

APOD: 2018 March 18 - Rotating Moon from LRO
Explanation: No one, presently, sees the Moon rotate like this. That's because the Earth's moon is tidally locked to the Earth, showing us only one side. Given modern digital technology, however, combined with many detailed images returned by the Lunar Reconnaissance Orbiter (LRO), a high resolution virtual Moon rotation movie has been composed. The above time-lapse video starts with the standard Earth view of the Moon. Quickly, though, Mare Orientale, a large crater with a dark center that is difficult to see from the Earth, rotates into view just below the equator. From an entire lunar month condensed into 24 seconds, the video clearly shows that the Earth side of the Moon contains an abundance of dark lunar maria, while the lunar far side is dominated by bright lunar highlands. Currently, over 20 new missions to the Moon are under active development from four different countries, most of which have expected launch dates either this year or next.

APOD: 2018 March 10 - Phases of the Moon
Explanation: Look at the Moon every night and its visible sunlit portion gradually changes. In phases progressing from New Moon to Full Moon to New Moon again, a lunar cycle or lunation is completed in about 29.5 days. Top left to bottom right, these frames show the range of lunar phases for 25 consecutive nights beginning on January 18, following an almost complete lunation. They skip the 2 days just after and 2 days before New Moon, when the lunar phase is at best a narrow crescent, close to the Sun and really hard to see. Of course, mostly clear Arizona night skies and a little help from a friend were required to complete this lunar cycle project, imaging in early evening for the first half and late evening and early morning for the second half of the lunation. For extra credit, the cycle was centered on the Full Moon of January 31. That was the second Full Moon in January, when the Moon was near lunar orbit perigee and took on reddish hues during a total lunar eclipse.

APOD: 2018 January 20 - Old Moon in the New Moon's Arms
Explanation: Also known as the Moon's "ashen glow" or the "Old Moon in the New Moon's arms", earthshine is earthlight reflected from the Moon's night side. This stunning image of earthshine from a young crescent moon was taken from Las Campanas Observatory, Atacama Desert, Chile, planet Earth near moonset on January 18. Dramatic atmospheric inversion layers appear above the Pacific Ocean, colored by the sunset at the planet's western horizon. But the view from the Moon would have been stunning, too. When the Moon appears in Earth's sky as a slender crescent, a dazzlingly bright, nearly full Earth would be seen from the lunar surface. A description of earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci.

APOD: 2017 December 3 - Full Moon Silhouettes
Explanation: Have you ever watched the Moon rise? The slow rise of a nearly full moon over a clear horizon can be an impressive sight. One impressive moonrise was imaged in early 2013 over Mount Victoria Lookout in Wellington, New Zealand. With detailed planning, an industrious astrophotographer placed a camera about two kilometers away and pointed it across the lookout to where the Moon would surely soon be making its nightly debut. The featured single shot sequence is unedited and shown in real time -- it is not a time lapse. People on Mount Victoria Lookout can be seen in silhouette themselves admiring the dawn of Earth's largest satellite. Seeing a moonrise yourself is not difficult: it happens every day, although only half the time at night. Each day the Moon rises about fifty minutes later than the previous day, with a full moon always rising at sunset. A good time to see a full moonrise will occur tonight at sunset as the Moon's relative closeness to Earth during a full phase -- called a supermoon -- will cause it to appear slightly larger and brighter than usual.

APOD: 2017 October 25 - Marius Hills: Holes in the Moon
Explanation: Could humans live beneath the surface of the Moon? This intriguing possibility was bolstered in 2009 when Japan's Moon-orbiting SELENE spacecraft imaged a curious hole beneath the Marius Hills region on the Moon, possibly a skylight to an underground lava tube. Follow-up observations by NASA's Lunar Reconnaissance Orbiter (LRO) indicated that the Marius Hills Hole (MHH) visually extends down nearly 100 meters and is several hundred meters wide. Most recently, ground penetrating radar data from SELENE has been re-analyzed to reveal a series of intriguing second echoes -- indicators that the extensive lava tubes exist under Marius Hills might extend down even kilometers and be large enough to house cities. Such tubes could shelter a future Moon colony from large temperature swings, micro-meteor impacts, and harmful solar radiation. Potentially, underground lava tubes might even be sealed to contain breathable air. These lava tubes likely formed when lunar volcanos were active billions of years ago. Pictured, the surface of Marius Hills region was captured in the 1960s by NASA's Lunar Orbiter 2 mission, while an inset image of the MHH is shown from NASA's continuing LRO. Several volcanic domes are visible, while Marius Crater is visible on the upper right.

APOD: 2017 January 17 - Fly Me to the Moon
Explanation: No, this is not a good way to get to the Moon. What is pictured is a chance superposition of an airplane and the Moon. The contrail would normally appear white, but the large volume of air toward the setting Sun preferentially knocks away blue light, giving the reflected trail a bright red hue. Far in the distance, to the right of the plane, is the young Moon. This vast world shows only a sliver of itself because the Sun is nearly lined up behind it. Captured two weeks ago, the featured image was framed by an eerie maroon sky, too far from day to be blue, too far from night to be black. Within minutes the impromptu sky show ended. The plane crossed the Moon. The contrail dispersed. The Sun set. The Moon set. The sky faded to black, only to reveal thousands of stars that had been too faint to see through the rustic red din.

APOD: 2016 November 13 - Super Moon vs Micro Moon
Explanation: What is so super about tomorrow's supermoon? Tomorrow, a full moon will occur that appears slightly larger and brighter than usual. The reason is that the Moon's fully illuminated phase occurs within a short time from perigee - when the Moon is its closest to the Earth in its elliptical orbit. Although the precise conditions that define a supermoon vary, tomorrow's supermoon will undoubtedly qualify because it will be the closest, largest, and brightest full moon in over 65 years. One reason supermoons are popular is because they are so easy to see -- just go outside at sunset and watch an impressive full moon rise! Since perigee actually occurs tomorrow morning, tonight's full moon, visible starting at sunset, should also be impressive. Pictured here, a supermoon from 2012 is compared to a micromoon -- when a full Moon occurs near the furthest part of the Moon's orbit -- so that it appears smaller and dimmer than usual. Given many definitions, at least one supermoon occurs each year, with another one coming next month (moon-th). However, a full moon will not come this close to Earth again until 2034.

APOD: 2016 October 21 - Full Moon in Mountain Shadow
Explanation: On October 15, standing near the summit of Hawaii's Mauna Kea and looking away from a gorgeous sunset produced this magnificent snapshot of a Full Moon rising within the volcanic mountain's shadow. An alignment across the Solar System is captured in the stunning scene and seeming contradiction of bright Moon in dark shadow. The triangular appearance of a shadow cast by a mountain's irregular profile is normal. It's created by the perspective of the distant mountaintop view through the dense atmosphere. Rising as the Sun sets, the antisolar point or the point opposite the Sun is close to the perspective's vanishing point near the mountain shadow's peak. But extending in the antisolar direction, Earth's conical shadow is only a few lunar diameters wide at the distance of the Moon. So October's Full Hunters Moon is still reflecting sunlight, seen through the mountain's atmospheric shadow but found too far from the antisolar point and the Earth's extended shadow to be eclipsed.

APOD: 2016 October 8 - Moon, Mercury, and Twilight Radio
Explanation: Sharing dawn's twilight with the Moon on September 29, Mercury was about as far from the Sun as it can wander, the innermost planet close to its maximum elongation in planet Earth's skies. In this colorful scene fleeting Mercury is joined by a waning sunlit lunar crescent and earthlit lunar nightside, the New Moon in the Old Moon's arms. Below is the Italian Medicina Radio Astronomical Station near Bologna with a low row of antennae that is part of Italy's first radio telescope array dubbed the "Northern Cross", and a 32-meter-diameter parabolic dish. Of course, moonwatchers won't have to rise in early morning hours on October 8. After sunset the Moon will be high and bright in evening skies, at its first quarter phase for International Observe the Moon Night.

APOD: 2016 September 16 - Full Moon over Brno
Explanation: After sunset this gorgeous full moon rose over Brno city in the Czech Republic on July 20, 2016. The panoramic image was made during a celebration of the 47th anniversary of the Apollo 11 lunar landing. A series of exposures captures the yellow hued lunar disk against the fading colors of twilight, with the 14th century Spilberk castle illuminated in the foreground. Of course, tonight's full moon is called the Harvest Moon. The closest full moon to the northern hemisphere's autumnal equinox, its traditional name has long been celebrated in story and song. Tonight's full lunar phase also coincides with a subtle, penumbral lunar eclipse, the Moon passing only through the Earth's diffuse, outer shadow.

APOD: 2016 July 10 - Moon Meets Jupiter
Explanation: What's that next to the Moon? Jupiter -- and its four largest moons. Skygazers around planet Earth enjoyed the close encounter of planets and Moon in 2012 July 15's predawn skies. And while many saw bright Jupiter next to the slender, waning crescent, Europeans also had the opportunity to watch the ruling gas giant pass behind the lunar disk, occulted by the Moon as it slid through the night. Clouds threaten in this telescopic view from Montecassiano, Italy, but the frame still captures Jupiter after it emerged from the occultation along with all four of its large Galilean moons. The sunlit crescent is overexposed with the Moon's night side faintly illuminated by Earthshine. Lined up left to right beyond the dark lunar limb are Callisto, Ganymede, Jupiter, Io, and Europa. In fact, Callisto, Ganymede, and Io are larger than Earth's Moon, while Europa is only slightly smaller. Last week, NASA's Juno became the second spacecraft ever to orbit Jupiter.

APOD: 2016 April 29 - Fermi's Gamma-ray Moon
Explanation: If you could only see gamma-rays, photons with up to a billion or more times the energy of visible light, the Moon would be brighter than the Sun! That startling notion underlies this novel image of the Moon, based on data collected by the Fermi Gamma-ray Space Telescope's Large Area Telescope (LAT) instrument during its first seven years of operation (2008-2015). Fermi's gamma-ray vision doesn't distinguish details on the lunar surface, but a gamma-ray glow consistent with the Moon's size and position is clearly found at the center of the false color map. The brightest pixels correspond to the most significant detections of lunar gamma-rays. Why is the gamma-ray Moon so bright? High-energy charged particles streaming through the Solar System known as cosmic rays constantly bombard the lunar surface, unprotected by a magnetic field, generating the gamma-ray glow. Because the cosmic rays come from all sides, the gamma-ray Moon is always full and does not go through phases. The first gamma-ray image of the Moon was captured by the EGRET instrument onboard the Compton Gamma-ray Observatory, launched 25 years ago.

APOD: 2016 February 1 - Find the Man in the Moon
Explanation: Have you ever seen the Man in the Moon? This common question plays on the ability of humans to see pareidolia -- imagining familiar icons where they don't actually exist. The textured surface of Earth's full Moon is home to numerous identifications of iconic objects, not only in modern western culture but in world folklore throughout history. Examples, typically dependent on the Moon's perceived orientation, include the Woman in the Moon and the Rabbit in the Moon. One facial outline commonly identified as the Man in the Moon starts by imagining the two dark circular areas -- lunar maria -- here just above the Moon's center, to be the eyes. Surprisingly, there actually is a man in this Moon image -- a close look will reveal a real person -- with a telescope -- silhouetted against the Moon. This featured well-planned image was taken in mid-January in Cadalso de los Vidrios in Madrid, Spain. Do you have a favorite object that you see in the Moon?

APOD: 2015 August 11 - A Blue Moon Halo over Antarctica
Explanation: Have you ever seen a halo around the Moon? Such 22 degree rings around the Moon -- caused by ice crystals falling in the Earth's atmosphere -- are somewhat rare. OK, but have you ever seen a blue moon? Given the modern definition of blue moon -- the second full moon occurring in a calendar month -- these are also rare. What is featured above might therefore be considered doubly rare -- a halo surrounding a blue moon. The featured image was taken late last month near Zhongshan Station in Antarctica. Visible in the foreground are a power generating house and a snowmobile. What might seem to be stars in the background are actually illuminated snowflakes near the camera.

APOD: 2015 August 7 - Full Earth, Full Moon
Explanation: The Moon was new on July 16. Its familiar nearside facing the surface of planet Earth was in shadow. But on that date a million miles away, the Deep Space Climate Observatory (DSCOVR) spacecraft's Earth Polychromatic Imaging Camera (EPIC) captured this view of an apparently Full Moon crossing in front of a Full Earth. In fact, seen from the spacecraft's position beyond the Moon's orbit and between Earth and Sun, the fully illuminated lunar hemisphere is the less familiar farside. Only known since the dawn of the space age, the farside is mostly devoid of dark lunar maria that sprawl across the Moon's perpetual Earth-facing hemisphere. Only the small dark spot of the farside's Mare Moscoviense (Sea of Moscow) is clear, at the upper left. Planet Earth's north pole is near 11 o'clock, with the North America visited by Hurricane Dolores near center. Slight color shifts are visible around the lunar edge, an artifact of the Moon's motion through the field caused by combining the camera's separate exposures taken in quick succession through different color filters. While monitoring the Earth and solar wind for space weather forcasts, about twice a year DSCOVR can capture similar images of Moon and Earth together as it crosses the orbital plane of the Moon.

APOD: 2015 July 31 - The ISS and a Colorful Moon
Explanation: Tonight's Full Moon, the second Full Moon in July, could be called a blue moon according to modern folklore. But this sharp and detailed mosaic, recorded with telescope and digital camera just before July's first Full Moon, actually does show a colorful lunar surface. The colors have been enhanced in the processed image but are real nonetheless, corresponding to real differences in the chemical makeup of the lunar surface. Also easy to see especially when the Moon is near full phase, bright rays from 85 kilometer wide Tycho crater at the upper right extend far across the lunar surface. Against the southern lunar highlands above and right of Tycho is an amazingly detailed silhouette of the International Space Station. Seen from Byron Bay, NSW Australia on June 30, the ISS lunar transit lasted about 1/3 of a second, captured with a fast shutter speed in burst mode.

APOD: 2015 April 3 - Sun and Moon Halo
Explanation: Two pictures captured on April 1 are combined in this creative day and night composite. Separated in time by about 10 hours the images otherwise match, looking along the coast at Östersund Sweden. The relative times were chosen to show the Sun and a nearly full Moon at the same place in the cold, early springtime sky. In the night scene Jupiter also shines above the waterfront lights, while Sun and Moon are both surrounded by a beautiful circular ice halo. The Sun and Moon halos really do align, each with an angular radius of 22 degrees. That radius is a constant, not determined by the brightness of Sun or Moon but only by the hexagonal geometry of atmospheric ice crystals and the reflection and refraction of light. Of course tomorrow, April 4, will find the Sun and Moon on opposite sides of planet Earth for a total lunar eclipse.

APOD: 2015 January 10 - The Windmill's Moon
Explanation: Seen from the Canary Island of Fuerteventura, this bright Full Moon rose at sunset. Reaching its full phase on the night of January 4/5, it was the first Full Moon of the new year and the first to follow December's solstice. Of course, in North America the first Full Moon of January has been known as the Wolf's Moon. But this Full Moon, posed in the twilight above an island of strong winds and traditional windmills, suggests another name. The telephoto image, taken at a distance from the foreground windmill, creates the dramatic comparison in apparent size for windmill and Full Moon.

APOD: 2014 September 8 - Super Moon vs Micro Moon
Explanation: What is so super about tomorrow's supermoon? Tomorrow, a full moon will occur that appears slightly larger and brighter than usual. The reason is that the Moon's fully illuminated phase occurs within a short time from perigee - when the Moon is its closest to the Earth in its elliptical orbit. Although the precise conditions that define a supermoon vary, given one definition, tomorrow's will be the third supermoon of the year -- and the third consecutive month that a supermoon occurs. One reason supermoons are popular is because they are so easy to see -- just go outside and sunset and watch an impressive full moon rise! Since perigee actually occurs today, tonight's sunset moonrise should also be impressive. Pictured above, a supermoon from 2012 is compared to a micromoon -- when a full Moon occurs near the furthest part of the Moon's orbit -- so that it appears smaller and dimmer than usual. Given many definitions, at least one supermoon occurs each year, with the next being 2015 August 30.

APOD: 2014 September 7 - Full Moon Silhouettes
Explanation: Have you ever watched the Moon rise? The slow rise of a nearly full moon over a clear horizon can be an impressive sight. One impressive moonrise was imaged in early 2013 over Mount Victoria Lookout in Wellington, New Zealand. With detailed planning, an industrious astrophotographer placed a camera about two kilometers away and pointed it across the lookout to where the Moon would surely soon be making its nightly debut. The above single shot sequence is unedited and shown in real time -- it is not a time lapse. People on Mount Victoria Lookout can be seen in silhouette themselves admiring the dawn of Earth's largest satellite. Seeing a moonrise yourself is not difficult: it happens every day, although only half the time at night. Each day the Moon rises about fifty minutes later than the previous day, with a full moon always rising at sunset. A good time to see a moonrise will occur at sunset on Tuesday as the Moon's relative closeness to Earth during a full phase -- called a supermoon -- will cause it to appear slightly larger and brighter than usual.

APOD: 2014 June 21 - Lisbon Honey Moon
Explanation: The Sun set on Friday the 13th as a full Honey Moon rose, captured in this well-planned time-lapse sequence. Lisbon, Portugal's Christ the King monument is in the foreground, about 6 kilometers distant from camera and telephoto lens. During the days surrounding today's solstice (June 21, 10:51 UT) the Sun follows its highest arc through northern hemisphere skies as it travels along the ecliptic plane. At night the ecliptic plane is low, and the Full Moon's path close to the ecliptic was also low, the rising Moon separating more slowly from the distant horizon. Northern moon watchers were likely to experience the mysterious Moon Illusion, the lunar orb appearing impossibly large while near the horizon. But the photo sequence shows the Moon's apparent size did not not change at all. Its light was initially scattered by the long line-of-sight through the atmosphere though, and a deeper reddened color gave way to a paler gold as the Full Moon rose into the night.

APOD: 2014 June 13 - A Strawberry Moon
Explanation: June's Full Moon (full phase on June 13, 0411 UT) is traditionally known as the Strawberry Moon or Rose Moon. Of course those names might also describe the appearance of this Full Moon, rising last month over the small Swedish village of Marieby. The Moon looks large in the image because the scene was captured with a long focal length lens from a place about 8 kilometers from the foreground houses. But just by eye a Full Moon rising, even on Friday the 13th, will appear to loom impossibly large near the horizon. That effect has long been recognized as the Moon Illusion. Unlike the magnification provided by a telescope or telephoto lens, the cause of the Moon illusion is still poorly understood and not explained by atmospheric optical effects, such as scattering and refraction. Those effects do produce the Moon's blushing color and ragged edge also seen in the photograph.

APOD: 2014 April 18 - Red Moon, Green Beam
Explanation: This is not a scene from a sci-fi special effects movie. The green beam of light and red lunar disk are real enough, captured in the early morning hours of April 15. Of course, the reddened lunar disk is easy to explain as the image was taken during this week's total lunar eclipse. Immersed in shadow, the eclipsed Moon reflects the dimmed reddened light of all the sunsets and sunrises filtering around the edges of planet Earth, seen in silhouette from a lunar perspective. But the green beam of light really is a laser. Shot from the 3.5-meter telescope at Apache Point Observatory in southern New Mexico, the beam's path is revealed as Earth's atmosphere scatters some of the intense laser light. The laser's target is the Apollo 15 retroreflector, left on the Moon by the astronauts in 1971. By determining the light travel time delay of the returning laser pulse, the experimental team from UC San Diego is able to measure the Earth-Moon distance to millimeter precision and provide a test of General Relativity, Einstein's theory of gravity. Conducting the lunar laser ranging experiment during a total eclipse uses the Earth like a cosmic light switch. With direct sunlight blocked, the reflector's performance is improved over performance when illuminated by sunlight during a normal Full Moon, an effect known as the real Full Moon Curse.

APOD: 2014 January 21 - Micro Moon over Super Moon
Explanation: Did you see the big, bright, beautiful Full Moon last Wednesday night? That was actually a Micro Moon! On that night, the smallest Full Moon of 2014 reached its full phase only a few hours from lunar apogee, the time of its the most distant point from Earth in the Moon's elliptical orbit. Of course, last year on the night of June 22, a Full Super Moon was near perigee, the closest point in its orbit. The relative apparent size of January 15's Micro Moon is compared to the June 22 Super Moon in the above composite image digitally superimposing telescopic images from Perugia, Italy. The difference in apparent size represents a difference in distance of just under 50,000 kilometers between apogee and perigee, given the Moon's average distance of about 385,000 kilometers. How long do you have to wait to see another Full Micro Moon? Until March 5, 2015, when the lunar full phase will again occur within a few hours of lunar apogee.

APOD: 2014 January 18 - Apogee's Full Moon
Explanation: This big, bright, beautiful Full Moon rose over Lick Observatory Wednesday night. Traditionally a full moon in January might be called the Wolf Moon. But this moon reached its full phase on January 16, 4:54 UT, within about 2 hours of apogee, the most distant point in its elliptical orbit around planet Earth. That also makes it the smallest full moon of 2014. Of course the difference in apparent size between the largest and smallest full moons is hard to see, because the difference in distance between lunar apogee and perigee, or closest point in the Moon's orbit, is only about 50,000 kilometers, while the Moon's average distance is around 385,000 kilometers. Though not by much, this apogee's full moon was also the smallest full moon of the last 1,000 years. It will keep that distinction until a slightly smaller full moon occurs close to apogee in 2154.

APOD: 2014 January 13 - A Trip to the Moon
Explanation: What would it be like to visit the Moon? The first major fictional cinematic film exploring this enduring transcultural fantasy was titled Le voyage dans la lune (A Trip to the Moon) and made in 1902, becoming one of the most popular movies of the early years of the twentieth century. The silent film starred the filmmaker Georges Melies himself and portrayed a club of astronomers voyaging to the Moon and back. Pictured above is a frame from the movie that has become an enduring icon for both film and space. Alluding to a bullseye trajectory, the Man in the Moon is caricatured as being struck by the human-built spaceship. The entire 14-minute film is now freely available. Visiting the Moon remained a very popular topic even 67 years later in 1969 when humans first made an actual voyage.

APOD: 2013 September 16 - Rotating Moon from LRO
Explanation: No one, presently, sees the Moon rotate like this. That's because the Earth's moon is tidally locked to the Earth, showing us only one side. Given modern digital technology, however, combined with many detailed images returned by the Lunar Reconnaissance Orbiter (LRO), a high resolution virtual Moon rotation movie has now been composed. The above time-lapse video starts with the standard Earth view of the Moon. Quickly, though, Mare Orientale, a large crater with a dark center that is difficult to see from the Earth, rotates into view just below the equator. From an entire lunar month condensed into 24 seconds, the video clearly shows that the Earth side of the Moon contains an abundance of dark lunar maria, while the lunar far side is dominated by bright lunar highlands. Two new missions are scheduled to begin exploring the Moon within the year, the first of which is NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE). LADEE, which launched just over a week ago, is scheduled to begin orbiting the Moon in October and will explore the thin and unusual atmosphere of the Moon. In a few months, the Chinese Chang'e 3 is scheduled to launch, a mission that includes a soft lander that will dispatch a robotic rover.

APOD: 2013 June 28 - A Super Moon's Halo
Explanation: A Full Perigee Moon rose as the Sun set last Sunday. At its closest to Earth it was, by just a bit, the year's brightest and largest Full Moon also known as a Super Moon. Seen from Punta Piedras, Argentina and the mouth of the Rio de La Plata, near Buenos Aires, the Super Moon's light created this magnificent circular lunar halo. Still, the size of a lunar halo is determined by the geometry of six sided water ice crystals in planet Earth's high, thin clouds. The crystals deflect the rays of moonlight more strongly through a minimum angle of 22 degrees. So this halo has an inner radius of 22 degrees, just like the halos of the less-than-super moons. Even more common than a Super Moon, beautiful 22 degree halos can be spotted at any time of year.

APOD: 2013 June 22 - Perigee's Full Moon
Explanation: A big, bright, beautiful Full Moon will rise at sunset on Sunday. Its exact full phase (June 23, 11:32 UT) will occur shortly before it reaches perigee, the closest point to Earth in the Moon's orbit, and make it the largest Full Moon of 2013. But such circumstances are not very rare. The full lunar phase falls near the Moon's orbit perigee about every 14 lunar months. That means the following Full Perigee Moon will be on August 10, 2014, the 14th Full Moon after June 23. On May 5, 2012, 14 Full Moons ago, this inspired telescopic night skyscape captured the Full Perigee Moon rising over Cape Sounion, Greece and the ancient Temple of Poseidon.

APOD: 2013 April 7 - The Moon's Saturn
Explanation: Just days after sharing the western evening sky with Venus in 2007, the Moon moved on to Saturn - actually passing in front of the ringed planet Saturn when viewed in skies over Europe, northern Africa, and western Asia. Because the Moon and bright planets wander through the sky near the ecliptic plane, such occultation events are not uncommon, but they are dramatic, especially in telescopic views. For example, in this sharp image Saturn is captured emerging from behind the Moon, giving the illusion that it lies just beyond the Moon's bright edge. Of course, the Moon is a mere 400 thousand kilometers away, compared to Saturn's distance of 1.4 billion kilometers. Taken with a digital camera and 20 inch diameter telescope at the Weikersheim Observatory in southern Germany, the picture is a single exposure adjusted to reduce the difference in brightness between Saturn and the cratered lunar surface.

APOD: 2012 November 29 - Super Moon vs Micro Moon
Explanation: Did you see the big, bright, beautiful Full Moon Wednesday night? That was actually a Micro Moon! On that night, the smallest Full Moon of 2012 reached its full phase only about 4 hours before apogee, the most distant point from Earth in the Moon's elliptical orbit. Of course, earlier this year on May 6, a Full Super Moon was near perigee, the closest point in its orbit. The relative apparent size of November 28's Micro Moon (right) is compared to the famous May 6 Super Moon in these two panels, matching telescopic images from Bucharest, Romania. The difference in apparent size represents a difference in distance of just under 50,000 kilometers between apogee and perigee, given the Moon's average distance of about 385,000 kilometers. How long do you have to wait to see another Full Micro Moon? Until January 16, 2014, when the lunar full phase will occur within about 3 hours of apogee.

APOD: 2012 November 6 - Methone: Smooth Egg Moon of Saturn
Explanation: Why is this moon shaped like a smooth egg? The robotic Cassini spacecraft completed the first flyby ever of Saturn's small moon Methone in May and discovered that the moon has no obvious craters. Craters, usually caused by impacts, have been seen on every moon, asteroid, and comet nucleus ever imaged in detail -- until now. Even the Earth and Titan have craters. The smoothness and egg-like shape of the 3-kilometer diameter moon might be caused by Methone's surface being able to shift -- something that might occur were the moon coated by a deep pile of sub-visual rubble. If so, the most similar objects in our Solar System would include Saturn's moons Telesto, Pandora, Calypso, as well as asteroid Itokawa, all of which show sections that are unusually smooth. Methone is not entirely featureless, though, as some surface sections appear darker than others. Although flybys of Methone are difficult, interest in the nature and history of this unusual moon is sure to continue.

APOD: 2012 November 5 - Saturn's Moon Dione in Slight Color
Explanation: Why does one half of Dione have more craters than the other? Start with the fact that Saturn's moon Dione has one side that always faces Saturn, and one side that always faces away. This is similar to Earth's Moon. This tidal locking means that one side of Dione always leads as the moon progresses in its orbit, while the other side always trails. Dione should therefore have undergone a significant number of impacts on its leading half. Strangely, the current leading half of Dione is less cratered than the trailing half. A leading explanation is that some crater-forming impacts were so large they spun Dione, changing the part that suffered the highest impact rate before the moon's spin again became locked. The above detailed image of Dione highlighting the moon's subtle hues is a meticulously-constructed mosaic -- by an dedicated amateur -- of pictures taken during the April 2010 flyby of Dione by NASA's robotic Cassini spacecraft.

APOD: 2012 November 3 - Hunter's Moon over the Alps
Explanation: A Full Moonset can be a dramatic celestial sight, and Full Moons can have many names. Late October's Full Moon, the second Full Moon after the northern hemisphere autumnal equinox, has been traditionally called the Hunter's Moon. According to lore, the name is a fitting one because this Full Moon lights the night during a time for hunting in preparation for the coming winter months. In this scene, last week's Hunter's Moon shines with a rich yellow light, setting as dawn comes to the Italian Alps. Topping out at over 11,000 feet, the snowy peak known as Rochemelon glows, just catching the first reddened light of the rising Sun.

APOD: 2012 September 1 - On a Blue Moon
Explanation: Rising at sunset, the gorgeous Full Moon of August 31 became the second Full Moon in a month. According to modern reckoning, that makes it a Blue Moon. In fact, parts of the Full Moon do look a little blue in this sharp lunar portrait. Taken just hours before the exact full phase in delightfully clear skies over Nottingham, UK, it features eye-catching bright rays extending from the prominent young crater Tycho in the Moon's southern hemisphere. The slightly color enhanced image also brings out subtle shades of blue, a real characteristic of terrain with a high content of titanium oxide and iron. The blue lunar terrain on the right includes the dark flat expanse of the Sea of Tranquility and the Apollo 11 landing site.

APOD: 2012 May 11 - Sun vs Super Moon
Explanation: The Super Moon wins, by just a little, when its apparent size is compared to the Sun in this ingenious composite picture. To make it, the Full Moon on May 6 was photographed with the same camera and telescope used to image the Sun (with a dense solar filter!) on the following day. Of course, on May 6 the Moon was at perigee, the closest point to Earth in its eliptical orbit, making it the largest Full Moon of 2012. Two weeks later, on May 20, the Moon will be near apogee, the most distant point in its orbit, so by then it will be nearly at its smallest apparent size. It will also be a dark New Moon on that date. And for some the New Moon will be surprisingly easy to compare to the Sun, because on May 20 the first solar eclipse of 2012 will be visible from much of Asia, the Pacific, and North America. Along a path 240 to 300 kilometers wide, the eclipse will be annular. Near apogee the smaller silhouetted Moon will fit just inside the bright solar disk.

APOD: 2012 May 10 - Green Flash and Super Moon
Explanation: It was really not about superheroes as on May 6 the much touted Super Moon, the largest Full Moon of 2012, rose over this otherwise peaceful harbor. And no supervillains were present either as boats gently rocked at their moorings near the checkerboard La Perdrix lighthouse on the coast of Brittany, France. But the rise of the Super Moon was preceded by a Green Flash, captured in the first frame of this timelapse video recorded that night. The cropped image of the frame, a two second long exposure, shows the strongly colored flash left of the lighted buoy near picture center. While the Super Moon was enjoyed at locations all around the world, the circumstances that produced the Green Flash were more restrictive. Green flashes for both Sun and Moon are caused by atmospheric refraction enhanced by long, low, sight lines and strong atmospheric temperature gradients often favored by a sea horizon.

APOD: 2012 March 24 - The New Moon in the Old Moon's Arms
Explanation: Also known as the Moon's ashen glow, Earthshine is Earthlight illuminating the Moon's night side. Taken on Nowruz, the March 20 equinox, from Esfahan, Iran, planet Earth, this telescopic image captures strong Earthshine from an old Moon. The darker earthlit disk is in the arms of a bright sunlit crescent. But the view from the Moon would have been enchanting too. When the Moon appears in Earth's sky as a slender crescent, a dazzlingly bright, nearly full Earth would be seen from the lunar surface. The Earth's brightness due to reflected sunlight is known to be strongly influenced by cloud cover. Still, a description of Earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci.

APOD: 2012 March 20 - Evolution of the Moon
Explanation: What is the history of the Moon? The Moon was likely created from debris expelled when a Mars-sized object violently impacted the Earth about 4.5 billion years ago. Just after gravitationally condensing, as imagined above, the glowing-hot surface of the Moon cooled and cracked. Rocks large and small continued to impact the surface, including a particularly large impact that created Aitken Basin about 4.3 billion years ago. A Heavy Bombardment period then continued for hundreds of millions of years, creating large basins all over the lunar surface. Over the next few billion years lava flowed into Earth-side basins, eventually cooling into the dark maria we see today. As always, relentless impacts continued, forming the craters we see today, slowly diminishing over the past billion years. Today the cooled Moon we know and love is as dark as coal and always keeps the same face toward Earth. Exactly how the Moon formed initially, and why lunar maria are only on the Earth side, remain active topics of research.

APOD: 2012 February 11 - A February Moon Halo
Explanation: Lighting the night last Tuesday, February's Full Moon is sometimes called the Snow Moon. But the Moon was not quite full in this mosaicked skyscape recorded on February 2 south of Budapest, Hungary, and there was no snow either. Still, thin clouds of ice crystals hung in the cold, wintry sky creating this gorgeous lunar halo. Refraction of moonlight by the six-sided crystals produce the slightly colored halo with its characteristic radius of 22 degrees. Just below the Moon is bright star Aldebaran. Also well within the halo at the right is the Pleiades star cluster. At the lower left, near the halo's edge lie the stars of Orion with bright Capella, alpha star of the constellation Auriga, just beyond the halo near the top of the frame.

APOD: 2012 January 20 - The Wolf's Moon
Explanation: A Full Moon rising can be a dramatic celestial sight, and Full Moons can have many names. Captured on January 8 from Östersund, Sweden, this evocative moonrise portrait might make you feel the cold of winter in the north. If you can also imagine wolves howling in the distance then you probably understand why Native Americans would have called it the Wolf Moon, their traditional name for the first Full Moon in January. The photographer reports that no wolves were heard though, as he watched this beautiful Full Moon rise in fading light over the eastern horizon, echoing the yellow color of the setting Sun. Of course, due this year on February 7, the next Full Moon will be the Snow Moon.

APOD: 2012 January 2 - Spot the Moon
Explanation: Where's the full Moon? Somewhere in this image, the Earth's Moon is hiding. The entire Moon is visible, in its completely full phase, in plain sight. Even the photographer's keen eye couldn't find it even though he knew exactly where to look -- only the long exposure of his camera picked it up -- barely. Although by now you might be congratulating yourself on finding it, why was it so difficult to see? For one reason, this photograph was taken during the total lunar eclipse last month, when the Earth's shadow made the Moon much dimmer than a normal full Moon. For another, the image, taken in Colorado, USA, was captured just 12 minutes before sunrise. With the Moon on the exact opposite side of the sky from the Sun, this meant that the Sun was just below the horizon, but still slightly illuminating the sky. Last, as the Moon was only about two degrees above the horizon, the large volume of air between the camera and the horizon scattered a lot of light away from the background Moon. Twelve minutes after this image was acquired the Sun peeked over the horizon and the Moon set.

APOD: 2011 November 27 - Shuttle Plume Shadow Points to the Moon
Explanation: Why would the shadow of a space shuttle launch plume point toward the Moon? In early 2001 during a launch of Atlantis, the Sun, Earth, Moon, and rocket were all properly aligned for this photogenic coincidence. First, for the space shuttle's plume to cast a long shadow, the time of day must be either near sunrise or sunset. Only then will the shadow be its longest and extend all the way to the horizon. Finally, during a Full Moon, the Sun and Moon are on opposite sides of the sky. Just after sunset, for example, the Sun is slightly below the horizon, and, in the other direction, the Moon is slightly above the horizon. Therefore, as Atlantis blasted off, just after sunset, its shadow projected away from the Sun toward the opposite horizon, where the Full Moon just happened to be.

APOD: 2011 March 20 - Parthenon Moon
Explanation: Did you see the Full Moon last night? Near the horizon, the lunar orb may have seemed to loom large, swollen in appearance by the famous Moon illusion. But the Full Moon really was a large Full Moon last night, reaching its exact full phase within an hour of lunar perigee, the point in the Moon's elliptical orbit closest to planet Earth. A similar near perigee Full Moon last occurred on December 12, 2008. The difference in the Moon's apparent size as it moves from perigee to apogee, its farthest point from Earth, is about 14 percent. Of course, a nearly Full Moon will rise again tonight, lighting the skies on the date of the Equinox or equal night. The Full Moon also looms large in this well-planned, telescopic lunar portrait. Captured earlier this year, the rising lunar orb is dramatically matched to the 2,500 year old Parthenon in Athens, Greece.

APOD: 2011 February 28 - Red Snow Moon over Edmonton
Explanation: What's hovering between those buildings? The Moon. The above image was taken two weeks ago as the full Snow Moon started to rise above Edmonton, Alberta, Canada. The odd coincidence between the angular size of the far distant Moon and the angular width of nearby buildings created a striking juxtaposition. Backing away from the buildings so to reduce their angular size was a key to planning the image. The temperature was so low, -25 C, that plumes of steam rose from neighboring oil refineries. The above image was taken during a momentary break in the plumes. The rising Moon appears red here for the same reason that a setting Sun appears red -- because blue light is preferentially scattered away by intervening air. In this case, the shimmering steam plumes likely also caused the Moon to appear slightly compressed. The next full moon, the full Worm Moon, will occur in mid-March.

APOD: 2010 September 24 - Equinox and the Harvest Moon
Explanation: Did you enjoy the moonlight last night? The Full Moon closest to autumnal equinox and the beginning of Fall is traditionally known as the Harvest Moon, rising opposite the Sun and illuminating fields at harvest time after sunset. This year's northern hemisphere autumnal equinox occurred yesterday, September 23rd, at 03:09 Universal Time. The Moon was at its full phase a mere 6 hours later -- exceptionally close for a Harvest Moon! Of course, the Moon still shines brightly through the night in surrounding days. In this picture from September 22nd, the lunar orb dominates the sky above a ruined church in Zsámbék, Hungary. Shining nearby, the brightest star is actually Jupiter, also opposite the Sun, seen here through thin clouds just left of the church wall.

APOD: 2010 June 6 - Lunokhod: Reflections on a Moon Robot
Explanation: It may look like some sort of cute alien robot, but it was created here on Earth, launched to the Moon in 1970, and now reflects laser light in a scientifically useful way. On November 17, 1970 the Soviet Luna 17 spacecraft landed the first roving remote-controlled robot on the Moon. Known as Lunokhod 1, it weighed just under 2,000 pounds and was designed to operate for 90 days while guided in real-time by a five person team near Moscow, USSR. Lunokhod 1 toured the lunar Sea of Rains (Mare Imbrium) for 11 months in one of the greatest successes of the Soviet lunar exploration program. This Lunokhod's operations officially ceased in 1971. Earlier this year, however, the position of the rover was recovered by NASA's moon-orbiting Lunar Reconnaissance Orbiter. Given that position, laser pulses from Earth were successfully bounced off the old robot's reflector. Bouncing laser pulses off of this and other lunar reflectors could yield range data to the moon accurate enough to track millimeter-sized deviations in the Moon's orbit, effectively probing lunar composition and testing gravitational theories.

APOD: 2010 May 16 - Crescent Venus and Moon
Explanation: There's something behind these clouds. Those faint graceful arcs, upon inspection, are actually far, far in the distance. They are the Earth's Moon and the planet Venus. Both the Moon and Venus are bright enough to be seen during the day, and both are quite capable of showing a crescent phase. To see Venus, which appears quite small, in a crescent phase requires binoculars or a telescope. In the above dramatic daytime image taken from Budapest, Hungary in 2004, the Moon and Venus shared a similar crescent phase a few minutes before the Moon eclipsed the larger but more distant world. Similarly, visible today in parts of Africa and Asia, a crescent Moon will again eclipse Venus during the day. About an hour after the above image was taken, Venus reappeared.

APOD: 2010 January 2 - Blue Moon Eclipse
Explanation: The International Year of Astronomy 2009 ended with a Blue Moon and a partial lunar eclipse, as the second Full Moon of December grazed the Earth's shadow on December 31st. The New Year's Eve Blue Moon eclipse was visible throughout Europe, Asia, Africa and parts of Alaska, captured in this two exposure composite in cloudy skies over Saint Bonnet de Mure, France. Playing across the Moon's southern reaches, the edge of Earth's umbra, or dark central shadow, appears on the right side along with the prominent ray crater Tycho. At maximum eclipse, the umbra covered only about 8 percent of the diameter of the lunar disk.

APOD: 2010 January 1 - Not a Blue Moon
Explanation: This bright Full Moon was captured on December 2nd, shining above a church overlooking the River Po, in Turin, Italy. It was the first Full Moon in December. Shining on celebrations of New Year's Eve, last night's Full Moon was the second Full Moon of December and so fits the modern definition of a Blue Moon - the second Full Moon in a month. Because the lunar cycle, Full Moon to Full Moon, spans 29.5 days, Blue Moons tend to occur in some month about every 2.5 years. Shining in the glare just above and right of December's first Full Moon is the Pleiades star cluster.

APOD: 2009 November 18 - Water Discovered in Moon Shadow
Explanation: Why is there water on the Moon? Last month, the LCROSS mission crashed a large impactor into a permanently shadowed crater near the Moon's South Pole. A plume of dust rose that was visible to the satellite, although hard to discern from Earth. The plume is shown above in visible light. Last week, the results of a preliminary chemical analysis gave a clear indication that the dust plume contained water. Such water is of importance not only for understanding the history of the Moon, but as a possible reservoir for future astronauts trying to live on the Moon for long periods. The source of the lunar water is now a topic of debate. Possible origins include many small meteorites, a comet, or primordial moon soil.

APOD: 2009 October 3 - Old Faithful Moon
Explanation: Scheduled to illuminate the landscape throughout the night tomorrow, October's bright Full Moon will also be called the Harvest Moon. Traditionally, the Harvest Moon is the Full Moon closest to the autumnal equinox. But in this vacation snapshot, the Full Moon could be called the "Old Faith-Full Moon". Taken on September 4, the picture combines the regularly occurring lunar phase with Old Faithful Geyser in Yellowstone National Park, named for its dependable erruptions. Shining on the well-known geyser's towering pillar from behind, the moonlight creates an eerie halo surrounding convoluted shapes. Faithfully, the Full Moon itself is bright enough to be seen through the dense swirling steam near the top.

APOD: 2009 September 28 - Water Discovered on the Moon
Explanation: Water has been discovered on the surface of the Moon. No lakes have been found, but rather NASA's Moon Mineralogy Mapper aboard India's new Chandrayaan-1 lunar orbiter radios back that parts of the Moon's surface absorb a very specific color of light identified previously only with water. Currently, scientists are trying to fit this with other facts about the Moon to figure out how much water is there, and even what form this water takes. Unfortunately, even the dampest scenarios leave our moon dryer than the driest of Earth's deserts. A fascinating clue being debated is whether the water signal rises and falls during a single lunar day. If true, the signal might be explainable by hydrogen flowing out from the Sun and interacting with oxygen in the lunar soil. This could leave an extremely thin monolayer of water, perhaps only a few molecules thick. Some of the resulting water might subsequently evaporate away in bright sunlight. Pictured above, the area near a crater on the far side of the Moon shows a relatively high abundance of water-carrying minerals in false-color blue. Next week, the new LCROSS satellite will release an impactor that will strike a permanently shadowed crater near the lunar south pole to see if any hidden water or ice sprays free there.

APOD: 2009 June 20 - Seaside Moon Mirage
Explanation: This surprising view of the Full Moon rising on June 7 was captured with a telephoto lens from a seaside balcony near Nice, France. The orange Moon's dark markings and odd shape put the photographer in mind of an alien creature's face staring down at the passing ship. Of course, the Moon's distorted appearance is due to the unusual bending (refraction) of light rays creating multiple images or mirages, similar to sunset and sunrise mirages. The effects are most pronounced when temperature layers in the atmosphere produce sharp changes in air density and refractive index. Acting over long sight-lines to the rising and setting Sun or Moon, the refraction significantly alters the path of light rays creating merged, distorted images. Such mirages are also associated with the Green Flash.

APOD: 2009 April 16 - Castle and Full Moon
Explanation: Clouds couldn't hide this bright Full Moon as it rose last week over the medieval castle of Tourrette-Levens near Nice, France. Exactly full on April 9 at 1456 UT, it followed the March equinox, making it the first Full Moon of spring in the north and autumn in the southern hemisphere. Known as the Easter Moon, it fixes the date for the celebration of Easter on the first Sunday after the first Full Moon of northern spring. Also called the Grass Moon or Egg Moon in the north, in the southern hemisphere, following the autumnal equinox, this Full Moon shines throughout the night as a Hunter's Moon.

APOD: 2009 February 23 - An Etruscan Vase Moon Rising
Explanation: What's happened to the Moon? Nothing, although from some locations, February's full moon, which occurred about two weeks ago, appeared strangely distorted as it rose. Visible in particular was a curiously inverted image section pinched off near the horizon, an effect dubbed the Etruscan vase by the pioneering science fiction writer Jules Verne for its familiar shape. This odd moon image piece was created by moonlight refracting through an atmospheric inversion layer on Earth where cold air was trapped near the surface. The photographer also reported that, as the moon rose, a red rim was faintly visible on the lower part of the moon, while a green rim appeared on the top. Similar to the Sun's famous green flash, these effects arise when the Earth's atmosphere acts like a prism, sending different colors of light on slightly different paths. The above image mosaic has been horizontally compressed by computer to fit a standard screen.

APOD: 2009 January 13 - Largest Full Moon of 2009
Explanation: A larger moon will not be seen this year. This past weekend, the largest full Moon of 2009 could be seen from almost any clear location on planet Earth at night. The large angular extent of the full Moon was caused by the Moon being unusually close to Earth during its full phase. Because the Moon circles the Earth in an elliptical orbit, its angular size depends on how close the Moon is to closest approach (perigee) or farthest distance (apogee). Even so, the Moon's was only about 15 percent larger in area and brightness than a more typical full Moon. In this image, a dramatically positioned Moon is seen rising above the Alps from Breil-sur-Roya in the southeast of France. Taken with an ordinary digital camera but extraordinary timing, the image also captured a crossing jet plane. The last full Moon, in 2008 December, was the largest full moon of 2008.

APOD: 2008 August 1 - Moon Games
Explanation: The Moon's measured diameter is around 3,476 kilometers (2,160 miles). But apparent angular size, or the angle covered by an object, can also be important to Moon enthusiasts. Angular size depends on distance, the farther away an object is, the smaller an angle it covers. Since the Moon is 400,000 kilometers away, its angular size is only about 1/2 degree, a span easily covered by the tip of your finger held at arms length, or a measuring tape held in the distance by a friend. Of course the Sun is much larger than the Moon, 400 times larger in fact, but today the New Moon will just cover the Sun. The total solar eclipse can be seen along a track across northern Canada, the Arctic, Siberia, and northern China. (A partial eclipse is visible from a broader region). Solar eclipses illustrate the happy coincidence that while the Sun is 400 times the diameter of the Moon, it is also 400 times farther away giving the Sun and Moon exactly the same angular size.

APOD: 2008 June 7 - June's Young Crescent Moon
Explanation: Serene skyviews were enjoyed across planet Earth earlier this week with a young crescent Moon low in the western sky just after sunset. Recorded on June 4, this colorful example includes a quiet beach in the foreground with the city lights of Lisbon, Portugal, and the Sintra Mountains along the horizon. Posing between cloud banks, the Moon's slender, sunlit arc represents only about 1 percent of the full lunar disc. The rest of the Moon's nearside is faintly visible though, illuminated by Earthshine. A waxing crescent Moon should also create some lovely western skies at dusk this weekend. The bright star in the sky near tonight's (Saturday's) Moon will actually be the planet Mars. On Sunday the Moon will move closer to a pair of celestial beacons, bright star Regulus and Saturn.

APOD: 2008 April 11 - At first he couldn't see the Moon
Explanation: At first, he couldn't see it, but searching with binoculars along a cloudy western horizon near sunset, photographer Laurent Laveder finally spotted a delicate lunar crescent. Captured in this dramatic picture on April 6th from Bretagne, France, the Moon was only 15 hours and 38 minutes old. Its slight, irregular, sunlit arc opens upward just above the dark cloud bank near picture center. Of course, a crescent Moon in the early evening sky is a lovely sight often enjoyed by many. But finding the Moon when its slim crescent is still less than about 24 hours past the New Moon phase requires careful timing and planning, a challenging project even for experienced observers. In this sighting, only about 0.8 percent of the Moon's disk appears illuminated. Laveder notes that this is the youngest Moon he has spotted in twenty years of skygazing and also offers this animation (Flash or gif) based on his images of the tantalizing celestial scene.

APOD: 2008 March 15 - Moon over Byzantium
Explanation: Hiding near the Sun, a slender crescent Moon is a difficult but rewarding sight. Look to the right (scroll right) and you can spot one in this twilight panorama across the Bosporus Strait and along the skyline of the historic city of Istanbul. Recorded on March 8, the Moon is a mere 22 hours young. A thin, curved edge of the Moon's illuminated surface is just visible poised in the western sky at sunset above the walls of Topkapi Palace. The palace was built in the reign of Ottoman Sultan Mehmed II, the 15th century conquerer of the city that was then Constantinople, capital of the Byzantine Empire. The well-lit domed building immediately to the left of the palace is Ayasofya (Hagia Sophia), a famous example of Byzantine architecture, now a museum. Still farther to the left is the Sultan Ahmed Mosque

APOD: 2007 December 23 - Moon and Mars Tonight
Explanation: The Full Moon and a brilliant, ruddy Mars will share the sky tonight. Skygazers can easily enjoy the celestial pairing as the two are separated by a degree or even less. In fact, seen from parts of northern North America and Europe, the Moon will actually occult (pass in front of) the Red Planet. Mars is so bright because it is near opposition, opposite the Sun in Earth's sky and near its closest approach to planet Earth. But Mars is not nearly as bright as the Moon, also opposite the Sun tonight. In this striking preview of tonight's sky show, backyard astronomer John Harms was able to photograph an almost Full Moon near Mars last month. His simple, single exposure relied on clouds to block some of the overwhelming moonlight.

APOD: 2007 October 25 - Apogee Moon, Perigee Moon
Explanation: Tonight, those blessed with clear skies can enjoy a glorious Full Moon, (exact full phase at 0452 UT, October 26). In fact, the Moon will reach its full phase within a few hours of perigee, the closest point in its elliptical orbit, making it the largest Full Moon of 2007. On April 3, the Full Moon was within hours of apogee, the farthest point in the lunar orbit, corresponding to the smallest Full Moon of 2007. The difference in apparent size between the largest and smallest Full Moon is quite dramatic and similar to this side by side comparison of the lunar apogee/perigee apparitions from 2006. But seen in the sky many months apart, the change is difficult to notice. Skygazers should also enjoy the Moon on Saturday, October 27, as it encounters the lovely Pleiades star cluster. Because the Moon will be so bright, it will be easiest to spot the Pleiades stars near the Moon with binoculars or a small telescope.

APOD: 2007 September 26 - Saguaro Moon
Explanation: A Full Moon rising can be a dramatic celestial sight, and Full Moons can have many names. For example, tonight's Full Moon, the one nearest the autumnal equinox in the northern hemisphere, is popularly called the Harvest Moon. According to lore the name is a fitting one because farmers could work late into the night at the end of the growing season harvesting crops by moonlight. In the same traditions, the Full Moon following the Harvest Moon is the Hunter's Moon. But, recorded on a trip to the American southwest, this contribution to compelling images of moonrise is appropriately titled Saguaro Moon.

APOD: 2007 June 3 - Shuttle Plume Shadow Points to Moon
Explanation: Why would the shadow of a space shuttle launch plume point toward the Moon? In early 2001 during a launch of Atlantis, the Sun, Earth, Moon, and rocket were all properly aligned for this photogenic coincidence. First, for the space shuttle's plume to cast a long shadow, the time of day must be either near sunrise or sunset. Next, just at sunset, the shadow is the longest and extends all the way to the horizon. Finally, during a Full Moon, the Sun and Moon are on opposite sides of the sky. Just after sunset, for example, the Sun is slightly below the horizon, and, in the other direction, the Moon is slightly above the horizon. Therefore, as Atlantis blasted off, just after sunset, its shadow projected away from the Sun toward the opposite horizon, where the Full Moon just happened to be.

APOD: 2007 June 2 - 3D Full Moon
Explanation: Get out your red/blue glasses and check out this satisfying stereo anaglyph of the Full Moon. A corresponding stereo image pair, intended for cross-eyed viewing, is also available through this link. Regardless of your preferred technique for stereo viewing, the 3D effect comes from combining pictures of the same scene taken at different angles -- mimicking the slightly different perspective of each eye. Perhaps surprisingly for Earthdwellers, getting two pictures of the Full Moon from different angles only requires a little patience. In this case, photographer Laurent Laveder used pictures taken months apart, one in November 2006 and one in January 2007. He relied on the Moon's continuous libration or wobble as it orbits to produce two shifted images of a Full Moon.

APOD: 2007 May 26 - The Moon's Saturn
Explanation: On May 22nd, just days after sharing the western evening sky with Venus, the Moon moved on to Saturn - actually passing in front of the ringed planet when viewed in skies over Europe, northern Africa, and western Asia. Because the Moon and bright planets wander through the sky near the ecliptic plane, such occultation events are not uncommon, but they are dramatic, especially in telescopic views. For example, in this sharp image Saturn is captured emerging from behind the Moon, giving the illusion that it lies just beyond the Moon's bright edge. Of course, the Moon is a mere 400 thousand kilometers away, compared to Saturn's distance of 1.4 billion kilometers. Taken with a digital camera and 20 inch diameter telescope at the Weikersheim Observatory in southern Germany, the picture is a single exposure adjusted to reduce the difference in brightness between Saturn and the cratered lunar surface.

APOD: 2007 March 20 - A Blue Crescent Moon from Space
Explanation: What's happening to the Moon? Drifting around the Earth in 2006 July, astronauts from the International Space Station (ISS) captured a crescent Moon floating far beyond the horizon. The captured above image is interesting because part of the Moon appears blue, and because part of the moon appears missing. Both effects are created by the Earth's atmosphere. Air molecules more efficiently scatter increasingly blue light, making the clear day sky blue for ground observers, and the horizon blue for astronauts. Besides reflecting sunlight, these atmospheric molecules also deflect moonlight, making the lower part of the moon appear to fade away. As one looks higher in the photograph, the increasingly thin atmosphere appears to fade to black.

APOD: 2007 March 2 - Solar Eclipse from the Moon
Explanation: Parts of Saturday's (March 3) lunar eclipse will be widely visible. For example, skywatchers in Europe, Africa, and western Asia will be able to see the entire spectacle of the Moon gliding through Earth's shadow, but in eastern North America the Moon will rise already in its total eclipse phase. Of course if you traveled to the Moon's near side, you could see the same event as a solar eclipse, with the disk of our fair planet Earth completely blocking out the Sun. For a moon-based observer's view, graphic artist Hana Gartstein (Haifa, Israel) offers this composite illustration. In the cropped version of her picture, an Apollo 17 image of Earth is surrounded with a red-tinted haze as sunlight streams through the planet's dusty atmosphere. Earth's night side remains faintly visible, still illuminated by the dark, reddened Moon, but the disk of the Earth would appear almost four times the size of the Sun's disk, so the faint corona surrounding the Sun would be largely obscured. At the upper left, the Sun itself is just disappearing behind the Earth's limb.

APOD: 2007 February 25 - The Far Side of the Moon
Explanation: Does this moon look familiar? Possibly not, even though it is Earth's Moon. Locked in synchronous rotation, the Moon always presents its well-known near side to Earth. But from lunar orbit, Apollo astronauts also grew to know the Moon's far side. This sharp picture from Apollo 16's mapping camera shows the eastern edge of the familiar near side (top) and the strange and heavily cratered far side of the Moon. Surprisingly, the rough and battered surface of the far side looks very different from the near side which is covered with smooth dark lunar maria. The likely explanation is that the far side crust is thicker, making it harder for molten material from the interior to flow to the surface and form the smooth maria.

APOD: 2006 September 11 - Eclipsed Moon Rising Over England
Explanation: Last Thursday, part of our Moon turned dark. The cause, this time, was not a partial lunar phase -- the Moon was full -- but rather that part of the Moon went into Earth's shadow. The resulting partial lunar eclipse was visible from the eastern Atlantic Ocean through Europe, Africa, and Asia and into the western Pacific Ocean. The darkest part of the lunar eclipse, when part of the Moon was completely shielded from sunlight, lasted about 90 minutes. Pictured above, a partially eclipsed Moon is seen rising over an estate in Huddersfield, England. The above image was taken far away from the house in the foreground, as only this would allow it to appear as angularly small as the half-degree Moon far in the background. A setting twilight Sun lit the foreground. The next eclipse of the Moon will occur in March 2007.

APOD: 2005 December 15 - Autumn Moon Encore
Explanation: Near its northernmost declination, tonight's Full Moon will be a special one, arcing high in northern hemisphere skies. But a Full Moon won't occur on this calendar date for another 19 years, a period known as the lunar Metonic cycle. September 15th's lunar phase and date were notable too, marking the return of a gibbous Moon rising over the High Sierra mountains. That scene was captured in Ansel Adams' famous photograph Autumn Moon from Glacier Point, Yosemite National Park. Earlier this year, Texas State University physicists Donald Olson, Russell Doescher and students were able to pinpoint the location and (formerly uncertain) date the original Ansel Adams photo was taken - September 15, 1948. Accordingly, their astronomical detective work predicted that the lunar alignment and waxing gibbous phase would be repeated on Thursday, September 15, 2005, exactly three 19-year Metonic cycles later. On that day, about 300 photographers gathered at Glacier Point to record Ansel Adams' Autumn Moon encore.

APOD: 2005 November 23 - Pandora: A Shepherd Moon of Saturn
Explanation: What does Saturn's small moon Pandora look like? To help find out, the robot Cassini spacecraft now orbiting Saturn passed about 50,000 kilometers from the unusual moon in early September. The highest resolution image of Pandora ever taken was then captured and is shown above in representative colors. Features as small as 300 meters can be discerned on 80-kilometer wide Pandora. Craters on Pandora appear to be covered over by some sort of material, providing a more smooth appearance than sponge-like Hyperion, another small moon of Saturn. Curious grooves and ridges also appear to cross the surface of the small moon. Pandora is partly interesting because, along with its companion moon Prometheus, it helps shepherd the particles of Saturn's F ring into a distinct ring.

APOD: 2005 August 26 - Full Moon, Green Rim
Explanation: July's Full Moon looks strangely darkened and distorted in this remarkable telescopic view. The image is one of a series recorded when the Moon was very near the horizon. The long sight-line through a turbulent atmosphere gives rise to the tantalizing optical effects, including the thin "mirage" shape that seems to float just above the Moon's upper edge. Also seen (more easily in the inset), along the Moon's upper edge is a noticeable green rim. Substantial atmospheric refraction produces this prism-like effect -- related to the more commonly witnessed green flash of the setting Sun. Careful inspection of the full image reveals a corresponding red rim along the lower edge, another intriguing signature of atmospheric refraction.

APOD: 2005 July 13 - Analemma of the Moon
Explanation: An analemma is that figure-8 curve you get when you mark the position of the Sun at the same time each day for one year. But the trick to imaging an analemma of the Moon is to understand that on average the Moon returns to the same position in the sky about 51 minutes later each day. So, if you photograph the Moon 51 minutes later on successive days, over one lunation or lunar month it will trace out an analemma-like curve as the actual position of the Moon wanders compared to the average -- due to the Moon's tilted and elliptical orbit. For this excellent demonstration of the lunar analemma, astronomer Rich Richins chose the lunar month containing this year's northern hemisphere summer solstice. The southernmost Full Moon rises at the lower right above the Organ Mountains in southern New Mexico, USA, with the New Moon phase at the upper left. The multiple exposure image required some digital manipulation, particularly to include thin crescent phases in daytime skies.

APOD: 2005 May 23 - A Wavemaker Moon in Saturn's Rings
Explanation: What causes small waves in Saturn's rings? Observations of rings bordering the Keeler gap in Saturn's rings showed unusual waves. Such waves were first noticed last July and are shown above in clear detail. The picture is a digitally foreshortened image mosaic taken earlier this month by the robot Cassini spacecraft now orbiting Saturn. The rings, made of many small particles, were somehow not orbiting Saturn in their usual manner. Close inspection of the image shows the reason - a small moon is orbiting in the Keeler gap. The previously unknown moon is estimated to span about seven kilometers and appears to have the same brightness as nearby ring particles. The gravity of the small moon likely perturbs the orbits of ring particles that come near it, causing them to shimmy back and forth after the moon passes. Since inner particles orbit more quickly than outer particles, only the leading particles of the inner rings and the trailing particles of the outer rings show the wave effect.

APOD: 2005 May 13 - When the Moon Was Young
Explanation: Remember when the Moon was young? It was just last Monday. On May 9th, this slender crescent Moon was recorded at a tender age of 34 hours and 18 minutes. Well, OK ... when calculating the lunar age during a lunation or complete cycle of phases - from New Moon to Full Moon and back to New Moon again - the Moon never gets more than around 29.5 days old. Still, a young Moon can be a rewarding sight, even for casual skygazers, though the slim crescent is relatively faint and only easy to see low in the west as the sky grows dark after sunset. Sighting this young Moon last Monday, lucky astronomer Stefan Seip was also treated to a very dramatic telescopic view of an airliner flying in front of the distant sunlit crescent. At a high altitude, the jet's stunning contrails reflect the strongly reddened light of the Sun setting below the western horizon.

APOD: 2005 March 18 - Moon, Mercury, Monaco
Explanation: Low on the western horizon after sunset, a slender crescent Moon and wandering planet Mercury join the lights of Menton and Monaco along the French Riviera. Astronomer Vincent Jacques took advantage of this gorgeous photo opportunity a week ago on March 11, when the Moon and Mercury were separated in the sky by just three degrees. Of course, the Moon in a slender crescent phase is always seen near the horizon, as is Mercury - a bright planet which can be otherwise difficult to glimpse as it never strays far from the Sun in Earth's sky. In the coming days good views of Mercury will indeed be fleeting as the solar system's innermost planet is rapidly dropping closer to the glare of the setting Sun. But tonight a waxing Moon will join another bright planet wandering overhead through the evening sky, Saturn.

APOD: 2004 November 13 - Moon Over Shiraz
Explanation: Early morning risers around the world have enjoyed the sight of bright planets in this week's predawn skies - further enhanced by the celestial spectacle of the waning crescent Moon. From some locations the Moon was seen to pass in front of Jupiter or Venus, a lunar occultation. Recorded near sunrise on November 10th from Shiraz, Iran, this eastern horizon view finds Jupiter (top) and a brilliant Venus in line with the Moon, a lovely conjunction of the three brightest objects in the night sky. Although the Moon has now fallen out of the early morning scene, Venus and Jupiter (along with a much fainter Mars) still precede the rising Sun above the eastern horizon.

APOD: 2004 October 21 - Apogee Moon, Perigee Moon
Explanation: Why don't these pieces fit? This third quarter Moon (left) and first quarter Moon were both photographed during the last lunar cycle or lunation with the same telescope and camera. But, simply combining the pictures into one sharp, full surface view would clearly be a problem. In fact, on October 6th the Moon's third quarter phase happened to occur near lunar apogee, the farthest point in the Moon's orbit. On September 21st, the first quarter phase fell close to lunar perigee, the Moon's closest approach to planet Earth. Viewed two weeks apart, the resulting difference in apparent sizes would not be noticed by casual skygazers, but the simultaneous side by side comparison makes it hard to ignore. Skygazers will likely notice the Moon next week though, as it slides through Earth's shadow during October 27th's total lunar eclipse.

APOD: 2004 July 31 - Tonight: A Blue Moon
Explanation: How often does a full moon occur twice in a single month? Exactly once in a Blue Moon. In fact, the modern usage of the term "Blue Moon" refers to the second Full Moon in a single month. Tonight's Blue Moon will be the first since November 2001. A Blue Moon typically occurs every few years. The reason for the rarity of the Blue Moon is that the 29.53 days between full moons is just slightly shorter than the number of days in the average month. Don't, however, expect the moon to look blue tonight! The term "Blue Moon" has recently been traced to an error in a magazine article in 1946. It is possible for the Moon to appear tinged by a blue hue, sometimes caused by fine dirt circulating in the Earth's atmosphere, possibly from a volcanic explosion. The above picture was taken not during a full moon but through a morning sky that appeared dark blue. The bright crescent is the only part directly exposed to sunlight - the rest of the Moon glows from sunlight reflected from the Earth. In this dramatic photo, however, the planet Jupiter is also visible along with its four largest moons.

APOD: 2003 December 25 - Venus and the 37 Hour Moon
Explanation: At Table Mountain Observatory, near Wrightwood California, USA on October 26, wild fires were approaching from the east. But looking toward the west just after sunset, astronomer James Young could still enjoy this comforting view of a young crescent Moon and brilliant Venus through the the fading twilight. Setting over the horizon of Mt. Baden-Powell, the thin crescent was only about 37 hours "old", or 37 hours after its exact New Moon phase. After disappearing from morning twilight in August, Venus was becoming prominent in its role in western skies as the evening star. A similar lovely pairing of thin crescent Moon and stunning evening star can be seen toward the west in today's evening twilight. Happy Holidays and Best Wishes from APOD!

APOD: 2003 November 22 - Moon AND Sun
Explanation: This composite image was made from 22 separate pictures of the Moon and Sun all taken from Chisamba, Zambia during the total phase of the 2001 June 21 solar eclipse. The multiple exposures were digitally processed and combined to simultaneously show a wealth of detail which no single camera exposure or naked-eye observation could easily reveal. Most striking are the incredible flowing streamers of the Sun's outer atmosphere or solar corona, notoriously difficult to see except when the new Moon blocks the bright solar disk. Features on the darkened near side of the Moon can also be made out, illuminated by sunlight reflected from a full Earth. A giant solar prominence seems to hang just beyond the Moon's eastern (left) edge while about one diameter farther east of the eclipsed Sun is the relatively faint (4th magnitude) star 1 Geminorum. The still active Sun will be totally eclipsed by the Moon tomorrow, but the path of the total eclipse will mostly cross the relatively inaccessible continent of Antarctica.

APOD: 2003 June 19 - The Moon Maiden
Explanation: Along the northwestern reaches of the lunar near side, the Sinus Iridum or Bay of Rainbows appropriately lies at the edge of the Moon's smooth, dark Sea of Rains (Mare Imbrium). In this sketch of the lunar surface around the Bay of Rainbows, the sun shines from the left, illuminating the arcing wall of the lava-floored bay. The bay's Cape Heraclides, seen here at the top of the sunlit arc, has been historically depicted as a moon maiden whose hair streams behind her as she gazes sunward across the bay. In the original Moon race - the race to map the Moon - this moon maiden first appeared in telescope-based drawings of the lunar surface by astronomer Giovanni Cassini in 1679. Still gazing across the lunar bay, the moon maiden inspired this drawing by modern day astronomer, Lucy Whitehouse. Done when she was 14, her sketch of the intriguing feature was made from the countryside in northern England, aided by a telescope equipped with a digital imaging eyepiece and a small television screen.

APOD: 2003 June 3 - The Milky Way Behind an Eclipsed Moon
Explanation: What's behind the Moon? Each month, our Moon passes in front of -- and outshines -- many an interesting star field. Exceptions occur during a new Moon and during a total eclipse. In the background of a new Moon is usually the Sun, an even brighter orb that even more easily outshines everything behind it, except during a total solar eclipse. Even the longest total solar eclipse lasts just a few minutes, while the Sun's corona still remains bright. During a total lunar eclipse, however, the full Moon dims and a majestic star field may present itself for an hour or more. Such was the case during the middle of last month, when a rare glimpse of an eclipsed Moon superposed in front of the disk of our home Milky Way Galaxy was captured. Although fully in the Earth's shadow, the eclipsed Moon is still the brightest object on the right. The above image was captured during sub-zero weather from the Teide 2003 expedition to Mirador del Pico Viejo, a mountain in the Canary Islands, Spain, off the northwest coast of Africa.

APOD: 2003 May 21 - Copper Moon, Golden Gate
Explanation: When the Moon rose over San Francisco's Golden Gate Bridge on May 15, both bridge and Moon were in already in Earth's shadow. Of course, the bridge is in the Earth's shadow nightly, while the Moon only has that opportunity about twice a year, during a lunar eclipse. And even though in western North America the total phase of the lunar eclipse began before moonrise, many in areas with clear skies came out to enjoy the spectacle. For this eclipse, skygazers reported a darker than normal, copper-colored Moon during totality. The dramatic color is evident in this multiple exposure of the reddened Moon rising, taken by astrophotographer Evad Damast. Damast viewed the eclipse from the Marin Headlands north and west of the famous bridge, looking back toward the bay and the city lights.

APOD: 2003 April 21 - A Halo Around the Moon
Explanation: Have you ever seen a halo around the Moon? This fairly common sight occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. Each ice crystal acts like a miniature lens. Because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the Moon Halo. A similar Sun Halo may be visible during the day. The picture was taken in Lansdowne, Pennsylvania, USA. The distant planet Jupiter appears by chance just to the left of the Moon. Exactly how ice-crystals form in clouds remains under investigation.

APOD: 2002 September 14 - X-Ray Moon
Explanation: This x-ray image of the Moon was made by the orbiting ROSAT (Röntgensatellit) Observatory in 1990. In this digital picture, pixel brightness corresponds to x-ray intensity. Consider the image in three parts: the bright hemisphere of the x-ray moon, the darker half of the moon, and the x-ray sky background. The bright lunar hemisphere shines in x-rays because it scatters x-rays emitted by the sun. The background sky has an x-ray glow in part due to the myriad of distant, powerful active galaxies, unresolved in the ROSAT picture but recently detected in Chandra Observatory x-ray images. But why isn't the dark half of the moon completely dark? It's true that the dark lunar face is in shadow and so is shielded from direct solar x-rays. Still, the few x-ray photons which seem to come from the moon's dark half are currently thought to be caused by energetic particles in the solar wind bombarding the lunar surface.

APOD: 2002 April 19 - The Old Moon in the New Moon's Arms
Explanation: Also known as the Moon's "ashen glow" or "the old Moon in the new Moon's arms", Earthshine is Earthlight reflected from the Moon's night side. This dramatic image of Earthshine and a young crescent Moon was taken by astrophotographer and APOD translator Laurent Laveder from the remote Pic du Midi Observatory on planet Earth. But the view from the Moon would have been stunning too. When the Moon appears in Earth's sky as a slender crescent, a dazzlingly bright, nearly full Earth would be seen from the lunar surface. The Earth's brightness, due to reflected sunlight, is strongly influenced by cloud cover and recent studies of Earthshine indicate that it is more pronounced during April and May. A description of Earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci.

APOD: 2002 February 9 - Moon Over Mongolia
Explanation: Fighting clouds and the glow of city lights, a young Moon shines over the western horizon of Mongolia's capital, Ulaan-Baatar. The thin sunlit crescent is about 2 days old and strongly over exposed in this image taken on March 10, 1997. The night side of the Moon is also visible due to earthshine - sunlight reflected from the Earth to the Moon. Just below the Moon, bright Saturn shines through the clouds. Skygazers will have a chance to watch the Moon actually pass in front of the ringed planet in February, March, and April this year. In fact, an excellent lunar occultation of Saturn will be visible from parts of North America on February 20th as Saturn disappears behind the dark limb of a first quarter Moon. Some may even take this opportunity to search for Saturn's lost ring.

APOD: 2001 September 6 - Moon AND Stars
Explanation: Here's something you don't see too often ... a detailed picture of the full Moon surrounded by a rich field of background stars. It's true that bright moonlight scattered by the atmosphere tends to mask faint stars, but pictures of the sunlit portion of the Moon made with earthbound telescopes or even with cameras on the lunar surface often fail to show any background stars at all. Why? Because the exposure times are too short. Very short exposures, lasting fractions of a second, are required to accurately record an image of the bright lunar surface. But the background stars (and galaxies!) such as those visible above are much fainter and need exposures lasting minutes to hours which would seriously overexpose the surface of the Moon. So, of course this stunning view really is a combination of two digital images -- a short exposure, registering the exquisite lunar surface details at full Moon, superposed on a separate very long exposure, made with the Moon absent from the star field. The final representation of Moon and background stars is very dramatic, even though it could not have been captured in a single exposure.

APOD: 2001 July 13 - Welcome to the Moon Hotel
Explanation: The most detailed proposal so far for a hotel and resort destination on the Moon (!) has been prepared by Dutch architect Hans-Jurgen Rombaut. The harsh lunar environment posed serious design challenges but the Moon's low, one-sixth-Earth gravity, and the absence of wind were an architectural boon allowing a much more slender and fragile-looking building than would have been possible on Earth. Illustrated here, the structure's two 160 meter high needle-like towers soar over the rim of a deep canyon as planet Earth hangs in the lunar sky. To shield the interior, Rombaut designed 50 centimeter thick walls with two outer layers of Moon rock and a 35 centimeter layer of water held between glass planes. The water absorbs energetic cosmic rays and along with the rock helps keep the temperature constant. Windows are framed as holes in the rock layers. Construction materials are intended to be manufactured on the Moon itself. This Moon Hotel design is welcomed by the international Lunar Explorers Society, LUNEX, who hope to construct a robotic Moon base by 2015, ultimately supporting a lunar village by 2040.

APOD: 2001 February 19 - Shuttle Plume Shadow Points to Moon
Explanation: Why would the shadow of a space shuttle launch plume point toward the Moon? Two weeks ago during the launch of Atlantis, the Sun, Earth, Moon, and rocket were all properly aligned for this photogenic coincidence. First, for the space shuttle's plume to cast a long shadow, the time of day must be either near sunrise or sunset. Next, just at sunset, the shadow is the longest and extends all the way to the horizon. Finally, during a Full Moon, the Sun and Moon are on opposite sides of the sky. Just after sunset, for example, the Sun is slightly below the horizon, and, in the other direction, the Moon is slightly above the horizon. Therefore, as Atlantis blasted off, just after sunset, its shadow projected away from the Sun toward the opposite horizon, where the Full Moon just happened to be.

APOD: 2000 October 13 - Eclipse Moon Trail
Explanation: Tonight, Friday the 13th, October's big, bright, beautiful full Moon will be in the sky, rising as the sun sets. A time exposure of this evening's full Moon would show a brilliant circular arc or Moon trail tracing its celestial path. In fact, this single, four hour long exposure from the evening of January 20 shows a full Moon trailing through hazy skies above Phoenix, Arizona, USA. Of course, the picture also shows something you won't see tonight -- a total lunar eclipse. A lunar eclipse is caused when the full moon enters Earth's shadow and as the eclipsed Moon's light grows steadily fainter, the Moon trail becomes narrow and dim. The total eclipse phase, when the Moon passes completely within Earth's shadow, occurs near the middle of this Moon trail arc. But even during totality, the Moon trail is visible and noticeably red. Normally illuminated by sunlight which falls directly on its surface, during a total lunar eclipse the Moon is still illuminated by sunlight filtered and refracted through Earth's atmosphere. The refracted light lends the eclipsed Moon a dim and reddish appearance.

APOD: 2000 September 2 - X Ray Moon
Explanation: This x-ray image of the Moon was made by the orbiting ROSAT (Röntgensatellit) Observatory in 1990. In this digital picture, pixel brightness corresponds to x-ray intensity. Consider the image in three parts: the bright hemisphere of the x-ray moon, the darker half of the moon, and the x-ray sky background. The bright lunar hemisphere shines in x-rays because it reflects x-rays emitted by the sun ... just as it shines at night by reflecting visible sunlight. The background sky has an x-ray glow in part due to the myriad of distant, powerful active galaxies, unresolved in the ROSAT picture but recently detected in Chandra Observatory x-ray images. But why isn't the dark half of the moon completely dark? It's true that the dark lunar face is in shadow and so is not reflecting solar x-rays. Still, the few x-ray photons which seem to come from the moon's dark half are currently thought to be caused by energetic particles in the solar wind bombarding the lunar surface.

APOD: 2000 July 28 - Moon And Venus Share The Sky
Explanation: July is drawing to a close and in the past few days, some early morning risers could have looked east and seen a crescent Moon sharing the pre-dawn skies with planets Jupiter and Saturn. Planet Mercury will also pass about 2 degrees from the thin waning crescent Moon just before sunrise near the eastern horizon on Saturday, July 29. And finally, on the evening of July 31st, Venus will take its turn near the crescent Moon. But this time it will be a day-old crescent Moon near the western horizon, shortly after sunset. In fact, on July 31 (August 1 Universal Time) the Moon will occult (pass in front of) Venus for northwestern observers in North America. This telescopic picture taken on 31 December 1997, shows a lovely young crescent Moon and brilliant crescent Venus in the early evening sky near Bursa, Turkey.

And what about the Sun? On Sunday, July 30, a partial eclipse of the Sun will be visible from some locations in North America.

APOD: 2000 June 17 - The Last Moon Shot
Explanation: In 1865 Jules Verne predicted the invention of a space capsule that could carry people. In his science fiction story "From the Earth to the Moon", he outlined his vision of a cannon in Florida so powerful that it could shoot a "Projectile-Vehicle" carrying three adventurers to the Moon. Over 100 years later, NASA, guided by Wernher Von Braun's vision, produced the Saturn V rocket. From a spaceport in Florida, this rocket turned Verne's fiction into fact, launching 9 Apollo Lunar missions and allowing 12 astronauts to walk on the Moon. Pictured is the last moon shot, Apollo 17, awaiting a night launch in December of 1972. Spotlights play on the rocket and launch pad while the full Moon looms in the background. Humans have not walked on on the lunar surface since.

APOD: 2000 April 6 - Venus, Moon, and Neighbors
Explanation: Rising before the Sun on February 2nd, astrophotographer Joe Orman anticipated this apparition of the bright morning star Venus near a lovely crescent Moon above a neighbor's house in suburban Phoenix, Arizona, USA. Fortunately, the alignment of bright planets and the Moon is one of the most inspiring sights in the night sky and one that is often easy to enjoy and share without any special equipment. Take tonight, for example. Those blessed with clear skies can simply step outside near sunset and view a young crescent Moon very near three bright planets in the west Jupiter, Mars, and Saturn. Jupiter will be the unmistakable brightest star near the Moon with a reddish Mars just to Jupiter's north and pale yellow Saturn directly above. Of course, these sky shows create an evocative picture but the planets and Moon just appear to be near each other -- they are actually only approximately lined up and lie in widely separated orbits. Unfortunately, next month's highly publicized alignment of planets on May 5th will be lost from view in the Sun's glare but such planetary alignments occur repeatedly and pose no danger to planet Earth.

APOD: 2000 January 13 - A Skygazers Full Moon
Explanation: This dramatically sharp picture of the full moon was recorded on 22 December, 1999 by astroimager Rob Gendler. Big, beautiful, bright, and evocative, it was the last full moon of the Y1.9Ks, pleasing and inspiring even casual skygazers. December's moon was special for another reason, as the full phase occurred on the day of the winter solstice and within hours of lunar perigee. The first full moon of the year 2000 will bring a special treat as well, presenting denizens of planet Earth with a total lunar eclipse. On Thursday evening, January 20, the moon will encounter the dark edge of Earth's shadow at 10:01 PM Eastern Time with the total eclipse phase beginning at 11:05 PM and lasting for 77 minutes. This lunar eclipse will be visible from North and South America and Western Europe (total phase begins at 4:05 AM GMT January 21).

APOD: December 22, 1999 - Perigee Moon, Apogee Moon
Explanation: Tonight, those blessed with clear skies can enjoy a glorious full moon, the last full moon of the "Y1.9K"s. In fact, tonight's moon will be a full-perigee-solstice moon, reaching its full phase and perigee (the closest point in its orbit) on the solstice, the first day of northern hemisphere winter. Anticipation of this celestial event has generated a flood of e-mail chasing the rumor that the full-perigee-solstice moon will be intensely bright. However, calculations show it will only be a little brighter than usual, and certainly not dramatically so. Why would it be brighter? Mostly because the moon appears bigger and brighter at perigee. The above illustration, based on Galileo spacecraft images, shows the approximate difference in apparent size between a full moon at perigee (left) and a full moon at apogee, the farthest point in the lunar orbit. The Earth and moon are also a few percent closer to the sun during northern winter, but the combined effects will cause tonight's full moon to appear only about 20% brighter than an average full moon. That difference is not even likely to be noticeable to the human eye.

APOD: December 8, 1999 - Moon Struck
Explanation: Craters produced by ancient impacts on the airless Moon have long been a familiar sight. But now observers have seen elusive optical flashes on the lunar surface - likely the fleeting result of impacting meteoroids. Orchestrated by David Dunham, president of the International Occultation Timing Association (IOTA), video recordings made with modest equipment and visual telescopic observations have, for the first time, detected and confirmed a total of six flashes on the Moon's dark side. The flashes, some initially as bright as a third magnitude star, were all seen within hours of the peak of this year's Leonid meteor shower. Their locations are indicated by the red Xs on this projection of the Moon as it appeared on the night of November 18. Similar flashes would have been difficult to see if viewed against the Moon's brightly lit portion. It has been estimated that the brightest flashes were made by meteoroids weighing around a tenth of a kilogram, resulting in lunar craters about one meter across. And ... the next chance to observe lunar impact flashes is coming up! Enterprising astronomers interested in long distance lunar prospecting should be monitoring the dark side of a nearly first quarter Moon during the Geminids meteor shower which will peak around December 13.

APOD: October 15, 1999 - Moon Crashers
Explanation: On July 31, 1964, Ranger 7 crashed into the Moon. Seventeen minutes before impact it snapped this picture - the first image of the Moon ever taken by a U.S. spacecraft. Of course Ranger 7 was intended to crash, transmitting close-up pictures of the lunar surface during its final moments. The Ranger program's goal was to begin high resolution mapping of the lunar surface in preparation for a future lunar landing. This first image covered 360 kilometers from top to bottom and is centered in the Mare Nubium (Sea of Clouds). The large crater at middle right, Alphonsus, is 108 kilometers in diameter.

On July 31, 1999, Lunar Prospector crashed into the Moon. During its successful 1 year mission to map the Moon's global properties from orbit, Lunar Prospector confirmed indications that water-ice could be trapped in permanently shadowed craters near the lunar poles. Its mission complete, controllers intentionally targeted the spacecraft to impact a crater wall, hoping that water could be more directly detected in the resulting debris cloud - although the chances of a successful detection were considered low. Astronomers analyzing the data recently announced that no visible signature of water was found, so the tantalizing case for water on the Moon remains open.

APOD: October 14, 1999 - Moon Over Eugenia
Explanation: Eugenia is an asteroid with a moon! This animation was constructed from infrared discovery images of the Eugenia-moon system taken in November 1998 using the Canada-France-Hawaii Telescope (CFHT). Main belt asteroid Eugenia, represented here as a central white patch, is a mere 215 kilometers in diameter. Its moon, seen at 5 separate positions around a clockwise orbit, is estimated to be 13 kilometers wide. An adaptive optics system was used with the CFHT, located atop Mauna Kea, Hawaii, to counteract the blurring effect of Earth's atmosphere making possible this premier discovery from a ground-based telescope. Only one other asteroid-moon system is known. Dactyl, moon of the asteroid Ida, was discovered by the Galileo spacecraft during a 1993 flyby.

Eugenia's moon has a nearly circular orbit with a radius of 1,190 kilometers which it completes once in 4.7 days. The orbit appears oval-shaped because it is tilted at a 45 degree angle to the line-of-sight. Knowing the moon's orbit allows astronomers to calculate the asteroid's mass. Combining mass and size determines the asteroid's density, which in this case gives a surprising result - Eugenia is found to have a density only 20% greater than water. The low density suggests that Eugenia itself is a porous "rubble pile" of rocks or composed mostly of water-ice with only a little additional rocky material.

APOD: May 31, 1999 - Uranus Moon 18
Explanation: The discovery was there for the taking. An image of Uranus taken by Voyager 2 as it passed the giant planet 13 years ago apparently recorded a moon that had since gone unnoticed. The image on which Uranus' 18th moon was discovered was freely available from NASA. Erich Karkoschka (U. Arizona) noticed the moon when comparing a 1986 photo to a recent one taken by the Hubble Space Telescope. The newly identified moon is hard to see but marked in the above photograph. Also visible are many other Uranian moons and background stars. The moon is the 18th known around Uranus, tying it with Saturn for the most around any planet.

APOD: April 19, 1999 - The Full Moon
Explanation: Earth has one moon. A symbol in famous love songs, movies, poems, and folklore, many myths about the Moon date back to ancient history. In fact, the name Monday originates from Moon-day. The Moon glows by light it reflects from the Sun and is frequently the brightest object in the night sky. The Moon orbits the Earth about once a month (moon-th) from about 1 light second away. The above-pictured Full Moon occurs when the Moon is nearly opposite to the Sun in its orbit. The Moon's diameter is about 1/4 that of the Earth, and from the Earth's surface appears to have almost exactly the same angular size as the Sun. Recent evidence indicates that the Moon formed from a colossal impact on the Earth about 4.5 billions of years ago, and therefore has a similar composition to the Earth. Humans walked on the Moon for the first time in 1969.

APOD: March 26, 1999 - Impact Moon
Explanation: The Moon's surface is covered with craters, scars of frequent impacts during the early history of the solar system. Now, recent results from the Lunar Prospector spacecraft support the idea that the Moon itself formed from the debris of a giant impact of a mars-sized planetary body with the Earth nearly 4.5 billion years ago. The impact theory of lunar origin can explain, for example, why Moon rocks returned by the Apollo missions have the same isotopic ratios as Earth rocks while the Moon seems deficient in heavy elements like iron. It can also explain a critical finding of the Lunar Prospector experiments - that the Moon's core is proportionally very small. If the Moon formed simply as a "sister world", its origin paralleling Earth's formation from the primordial solar nebula, it should have similar iron content and relative core size. But material blasted from the surface of Earth by an impacting body would lack the iron and heavy elements which had settled to the Earth's core yet retain similar ratios of chemical isotopes. A fraction of this debris cloud would remain in Earth orbit ultimately forming the Moon.

APOD: January 29, 1999 - The Moon In January
Explanation: Reckoning dates by Universal Time, the next full moon will be on Sunday, January 31. Since the last was on January 2nd, Sunday's full moon will be the second this month. Perhaps only in recent times, the term "Blue Moon" has come to mean the second full moon in a month, joining a list of folklore names for the brightest lunar phase. Aren't Blue Moons extremely rare? Well, the moon's phases repeat every 29.5 days and most months have 30 or 31 days, so a Blue Moon is certainly possible if not a common event. In fact, the next (and last) Blue Moon in 1999 will occur in March, leaving February without a full moon at all. This sharp telescopic view of a waning crescent moon was recorded on January 12th by the European Southern Observatory's new WFI camera.

APOD: December 13, 1998 - Blasting Off from the Moon
Explanation: How did the astronauts get back from the Moon? The Lunar Module that landed two astronauts on the Moon actually came apart. The top part containing the astronauts carried additional rocket fuel which allowed it to blast away, leaving the bottom part on the Moon forever. The top part would later meet up with the Command Module and its astronaut pilot, which were continually orbiting the Moon. All would then return to Earth together. The above picture was taken by a robot TV camera left on the Moon by the crew of Apollo 16. The frame above captures the top part of the Lunar Module just at it was blasting off.

APOD: May 3, 1998 - Standing on the Moon
Explanation: Humans once walked on the Moon. Pictured above is the second person to stand on the lunar surface: Edwin "Buzz" Aldrin. During this Apollo 11 mission, Neil Armstrong (the first person to walk on the moon) and Buzz Aldrin landed on the Moon while Michael Collins circled in the Command Module above. The lunar team erected a plaque on the surface that reads: HERE MEN FROM THE PLANET EARTH FIRST SET FOOT UPON THE MOON JULY 1969 A.D. WE CAME IN PEACE FOR ALL MANKIND. The Apollo missions demonstrated that it is possible to land humans on the Moon and return them safely.

APOD: January 29, 1998 - The Earth-Moon System
Explanation: This evocative mosaic image of the Earth-Moon system was recorded by NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft earlier this month. The relative sizes shown are appropriate for viewing both the Earth and Moon from a distance of about 250,000 miles, although the apparent brightness of the Moon has been increased by about a factor of five for the sake of appearances. This space-based perspective is a unique one, the bland and somber Lunar Southern Hemisphere contrasting strongly with blue oceans, swirling clouds, and the bright icy white continent of Antarctica on planet Earth. Though its lack of atmosphere and oceans make it relatively dull looking, the Earth's moon is one of the largest moons in the solar system - even larger than the planet Pluto. During this recent flyby of the Earth-Moon system, the NEAR spacecraft used Earth's gravity to deflect it towards its ultimate destination, the Asteroid 433 Eros. It is scheduled to arrive at Eros in January 1999.

APOD: January 3, 1998 - The Barren Moon
Explanation: The above photo, taken as the Apollo 17 astronauts orbited the Moon in 1972, depicts the stark lunar surface around the Eratosthenes and Copernicus craters. Many similar images of a Moon devoid of life are familiar to denizens of the space age. Contrary to this modern perception, life on the Moon was reported in August of 1835 in a series of sensational stories first published by the New York Sun - apparently intended to improve the paper's circulation. These descriptions of lunar life received broad credence and became one of the most spectacular hoaxes in history. Supposedly based on telescopic observations, the stories featured full, lavish accounts of a Moon with oceans and beaches, teeming with plant and animal life and climaxing with the report of sightings of groups of winged, furry, human-like creatures resembling bats! Within a month the hoax had been revealed but the newspaper continued to enjoy an increased readership. Though barren, the Moon remains a popular setting for science fiction stories and extra-terrestrial adventures. It has now been 25 years since Apollo 17 ended an era of human exploration of Earth's Moon.

APOD: September 16, 1997 - Moon Over Mongolia
Explanation: Fighting clouds and the glow of city lights, a young Moon shines over the western horizon of Mongolia's capital Ulaan-Baatar. The thin sunlit crescent is 1.5 days old and strongly over exposed in this image taken on March 10. The night side of the moon is also visible due to Earthshine - sunlight reflected from the Earth to the Moon. Just below the Moon, bright Saturn shines through the clouds. Early morning risers can see the Moon near Saturn this week. In fact, from North America the Moon can be seen to pass in front of the ringed planet on Thursday morning, September 18th.

APOD: June 7, 1997 - Apollo 15: Driving on the Moon
Explanation: Apollo 15 astronaut James Irwin works on the first Lunar Roving Vehicle, before he and fellow astronaut David Scott take it out for a drive. Sloping up behind the lunar module "Falcon" on the left are lunar mountains Hadley Delta and Apennine Front, while about 5 kilometers behind Irwin is St. George Crater. The explorations conducted during the Apollo lunar missions discovered much about our Moon, including that the Moon is made of ancient rock, that the Moon's composition is similar to Earth's, that life is not evident there, that the Moon underwent a great hot melting in its distant past, that the Moon has suffered from numerous impacts as shown by its craters, and that the Moon's surface is covered by a layer of rock fragments and dust.

APOD: May 4, 1997 - The Last Moon Shot
Explanation: In 1865 Jules Verne predicted the invention of a space capsule that could carry people. In his science fiction story "From the Earth to the Moon", he outlined his vision of a cannon in Florida so powerful that it could shoot a "Projectile-Vehicle" carrying three adventurers to the Moon. Over 100 years later, NASA, guided by Wernher Von Braun's vision, produced the Saturn V rocket. From a spaceport in Florida, this rocket turned Verne's fiction into fact, launching 9 Apollo Lunar missions and allowing 12 astronauts to walk on the Moon. Pictured is the last moon shot, Apollo 17, awaiting a night launch in December of 1972. Spotlights play on the rocket and launch pad while the full Moon looms in the background. Humans have not walked on the lunar surface since. Should we return to the Moon?

APOD: July 31, 1996 - A Violet Moon
Explanation: Checking out the Galileo spacecraft's cameras during its December 1992 flyby of Earth's Moon, controllers took this dramatically illuminated picture through a violet filter. The view looks down on the Moon's north polar region with the Sun shining from the left at a low angle and the direction toward the moon's North pole toward the lower right. Across the image upper left stretches the smooth volcanic plain of the Mare Imbrium. Pythagoras crater, 65 miles wide, is near the center of the image -- mostly in shadow, its central peak just catches the sunlight. Yesterday, the Moon made its closest approach to Earth and was full for the second time in July (as reckoned by UT dates). The closest point in the Moon's orbit is referred to as Lunar Perigee, a mere 221,797 miles at 8 hours UT. The second full moon in a month is known as a "Blue Moon".

APOD: July 30, 1996 - Tonight: A Blue Moon
Explanation: How often does a Full Moon occur twice in a single month? Exactly once in a Blue Moon. In fact, the modern usage of the term "Blue Moon" refers to the second Full Moon in a single month. Tonight's Blue Moon (Universal Time) will be the first since September 1993. A Blue Moon typically occurs every few years. The reason for the rarity of the Blue Moon is that the 29.53 days between full moons is just slightly shorter than the number of days in the average month. Don't, however, expect the moon to look blue tonight! The term "Blue Moon" is thought to derive from common language expressions used hundreds of years ago. It is possible for the Moon to appear tinged by a blue hue, sometimes caused by fine dirt circulating in the Earth's atmosphere, possibly from a volcanic explosion. The above picture is of our Moon taken was taken in a dark blue morning sky. The bright crescent is the only part directly exposed to sunlight - the rest of the Moon glows from sunlight reflected from the Earth. In this dramatic photo, however, the planet Jupiter is also visible along with its four largest moons.

APOD: June 9, 1996 - Blasting Off From the Moon
Explanation: How did the astronauts get back from the Moon? The Lunar Module that landed two astronauts on the Moon actually came apart. The top part containing the astronauts carried additional rocket fuel which allowed it to blast away, leaving the bottom part on the Moon forever. The top part would later meet up with the Command Module and its astronaut pilot, which were continually orbiting the Moon. All would then return to Earth together. The above picture was taken by a robot TV camera left on the Moon by the crew of Apollo 16. The frame above captures the top part of the Lunar Module just at it was blasting off.

APOD: February 23, 1996 - Apollo 15: Driving on the Moon
Explanation: Apollo 15 astronaut James Irwin works on the first Lunar Roving Vehicle, before he and fellow astronaut David Scott take it out for a drive. Sloping up behind the lunar module "Falcon" on the left are lunar mountains Hadley Delta and Apennine Front, while about 5 kilometers behind Irwin is St. George Crater. The explorations conducted during the Apollo lunar missions discovered much about our Moon, including that the Moon is made of ancient rock, that the Moon's composition is similar to Earth's, that life is not evident there, that the Moon underwent a great hot melting in its distant past, that the Moon has suffered from numerous impacts as shown by its craters, and that the Moon's surface is covered by a layer of rock fragments and dust.

APOD: September 9, 1995 - The Last Moon Shot
Explanation: In 1865 Jules Verne predicted the invention of a space capsule that could carry people. In his science fiction story "From the Earth to the Moon", he outlined his vision of constructing a cannon in Florida so powerful that it could shoot a "Projectile-Vehicle" carrying three adventurers to the Moon. Over 100 years later, NASA, guided by Wernher Von Braun's vision, produced the Saturn V rocket. This rocket turned Verne's fiction into fact, launching 9 Apollo Lunar missions and allowing 12 astronauts to walk on the Moon. Pictured above is the last moon shot, Apollo 17, awaiting a night launch in December of 1972. Spot lights play on the rocket and launch pad while the full Moon looms in the background. Humans have not walked on the lunar surface since. Should we return to the Moon?

APOD: September 3, 1995 - Earth's Moon, A Familiar Face
Explanation: The above mosaic of the Earth's Moon was compiled from photos taken by the spacecraft Clementine in 1994. This image represents the side of the Moon familiar to Earth dwellers. The Moon revolves around the Earth about once every 28 days. Since its rate of rotation about its axis is also once in 28 days, it always keeps the same face toward the Earth. As the Moon travels around its orbit, the Earth based view of the half of the Moon that faces the Sun changes causing the regular monthly progression of Lunar phases. Humans first crashed a spacecraft into the Moon in 1959, but the first humans to reach the Moon landed in 1969. There are now golf balls on the Moon.