Astronomy Picture of the Day Search Results for "Pleiades"

APOD: 2025 August 25 – The Meteor and the Star Cluster
Explanation: Sometimes even the sky surprises you. To see more stars and faint nebulosity in the Pleiades star cluster (M45), long exposures are made. Many times, less interesting items appear on the exposures that were not intended -- but later edited out. These include stuck pixels, cosmic ray hits, frames with bright clouds or Earth's Moon, airplane trails, lens flares, faint satellite trails, and even insect trails. Sometimes, though, something really interesting is caught by chance. That was just the case a few weeks ago in al-Ula, Saudi Arabia when a bright meteor streaked across during an hour-long exposure of the Pleiades. Along with the famous bright blue stars, less famous and less bright blue stars, and blue-reflecting dust surrounding the star cluster, the fast rock fragment created a distinctive green glow, likely due to vaporized metals.

APOD: 2025 July 8 – The Pleiades in Red and Blue
Explanation: If you have looked at the sky and seen a group of stars about the size of the full Moon, that's the Pleiades (M45). Perhaps the most famous star cluster in the sky, its brightest stars can be seen even from the light-polluted cities. But your unaided eye can also see its nebulosity -- the gas and dust surrounding it -- under dark skies. However, telescopes can catch even more. The bright blue stars of the Pleiades, also known as the Seven Sisters, light up their surrounding dust, causing it to appear a diffuse blue that can only be seen under long exposures. But that's not all. The cosmic dust appears to stretch upward like ethereal arms. And the entire structure is surrounded by a reddish glow from the most abundant element in the universe: hydrogen. The featured image is composed of nearly 25 hours of exposure and was captured last year from Starfront Observatory, in Texas, USA

APOD: 2025 April 8 – Moon Visits Sister Stars
Explanation: Sometimes, the Moon visits the Pleiades. Technically, this means that the orbit of our Moon takes it directly in front of the famous Pleiades star cluster, which is far in the distance. The technical term for the event is an occultation, and the Moon is famous for its rare occultations of all planets and several well-known bright stars. The Moon's tilted and precessing orbit makes its occultations of the Seven Sisters star cluster bunchy, with the current epoch starting in 2023 continuing monthly until 2029. After that, though, the next occultation won't occur until 2042. Taken from Cantabria, Spain on April 1, the featured image is a composite where previous exposures of the Pleiades from the same camera and location were digitally added to the last image to bring up the star cluster's iconic blue glow.

APOD: 2025 March 10 – NGC 1499: The California Nebula
Explanation: Could Queen Calafia's mythical island exist in space? Perhaps not, but by chance the outline of this molecular space cloud echoes the outline of the state of California, USA. Our Sun has its home within the Milky Way's Orion Arm, only about 1,000 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

APOD: 2025 March 5 – Seven Sisters versus California
Explanation: On the right, dressed in blue, is the Pleiades. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3,000 stars, is about 400 light years away, and only 13 light years across. Surrounding the stars is a spectacular blue reflection nebula made of fine dust. A common legend is that one of the brighter stars faded since the cluster was named. On the left, shining in red, is the California Nebula. Named for its shape, the California Nebula is much dimmer and hence harder to see than the Pleiades. Also known as NGC 1499, this mass of red glowing hydrogen gas is about 1,500 light years away. Although about 25 full moons could fit between them, the featured wide angle, deep field image composite has captured them both. A careful inspection of the deep image will also reveal the star forming region IC 348 and the molecular cloud LBN 777 (the Baby Eagle Nebula).

APOD: 2025 January 27 – Pleiades over Half Dome
Explanation: Stars come in bunches. The most famous bunch of stars on the sky is the Pleiades, a bright cluster that can be easily seen with the unaided eye. The Pleiades lies only about 450 light years away, formed about 100 million years ago, and will likely last about another 250 million years. Our Sun was likely born in a star cluster, but now, being about 4.5 billion years old, its stellar birth companions have long since dispersed. The Pleiades star cluster is pictured over Half Dome, a famous rock structure in Yosemite National Park in California, USA. The featured image is a composite of 28 foreground exposures and 174 images of the stellar background, all taken from the same location and by the same camera on the same night in October 2019. After calculating the timing of a future juxtaposition of the Pleiades and Half Dome, the astrophotographer was unexpectedly rewarded by an electrical blackout, making the background sky unusually dark.

APOD: 2024 December 9 – Pleiades: The Seven Sisters Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as large and clear as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen with the unaided eye even from the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured 23-hour exposure, taken from Fagagna, Italy covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six of the sister stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2024 September 29 – Seven Dusty Sisters
Explanation: Is this really the famous Pleiades star cluster? Known for its iconic blue stars, the Pleiades is shown here in infrared light where the surrounding dust outshines the stars. Here, three infrared colors have been mapped into visual colors (R=24, G=12, B=4.6 microns). The base images were taken by NASA's orbiting Wide Field Infrared Survey Explorer (WISE) spacecraft. Cataloged as M45 and nicknamed the Seven Sisters, the Pleiades star cluster is by chance situated in a passing dust cloud. The light and winds from the massive Pleiades stars preferentially repel smaller dust particles, causing the dust to become stratified into filaments, as seen. The featured image spans about 20 light years at the distance of the Pleiades, which lies about 450 light years distant toward the constellation of the Bull (Taurus).

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 15 - Late Night Vallentuna
Explanation: Bright Mars and even brighter Jupiter are in close conjunction just above the pine trees in this post-midnight skyscape from Vallentuna, Sweden. Taken on August 12 during a geomagnetic storm, the snapshot records the glow of aurora borealis or northern lights, beaming from the left side of the frame. Of course on that date Perseid meteors rained through planet Earth's skies, grains of dust from the shower's parent, periodic comet Swift-Tuttle. The meteor streak at the upper right is a Perseid plowing through the atmosphere at about 60 kilometers per second. Also well-known in Earth's night sky, the bright Pleiades star cluster shines below the Perseid meteor streak. In Greek myth, the Pleiades were seven daughters of the astronomical titan Atlas and sea-nymph Pleione. The Pleiades and their parents' names are given to the cluster's nine brightest stars.

APOD: 2024 August 2 - Mars Passing By
Explanation: As Mars wanders through Earth's night, it passes about 5 degrees south of the Pleiades star cluster in this composite astrophoto. The skyview was constructed from a series of images captured over a run of 16 consecutive clear nights beginning on July 12. Mars' march across the field of view begins at the far right, the planet's ruddy hue showing a nice contrast with the blue Pleiades stars. Moving much faster across the sky against the distant stars, the fourth planet from the Sun easily passes seventh planet Uranus. Red planet Mars and the ice giant world were in close conjunction, about 1/2 degree apart, on July 16. Continuing its rapid eastward trek, Mars has now left the sister stars and outer planet behind though, passing north of red giant star Aldebaran. Mars will come within about 1/3 degree of Jupiter in planet Earth's sky on August 14.

APOD: 2024 February 25 – A Phoenix Aurora over Iceland
Explanation: All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet September night, much of that night's auroras had died down. Suddenly, unexpectedly, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, surprisingly, pareidoliacally, the night lit up with an amazing shape reminiscent of a giant phoenix. With camera equipment at the ready, two quick sky images were taken, followed immediately by a third of the land. The mountain in the background is Helgafell, while the small foreground river is called Kaldá, both located about 30 kilometers north of Iceland's capital Reykjavík. Seasoned skywatchers will note that just above the mountain, toward the left, is the constellation of Orion, while the Pleiades star cluster is also visible just above the frame center. The 2016 aurora, which lasted only a minute and was soon gone forever -- would possibly be dismissed as a fanciful fable -- were it not captured in the featured, digitally-composed, image mosaic.

APOD: 2024 January 29 – The Pleiades: Seven Dusty Sisters
Explanation: The well-known Pleiades star cluster is slowly destroying part of a passing cloud of gas and dust. The Pleiades is the brightest open cluster of stars on Earth's sky and can be seen from almost any northerly location with the unaided eye. Over the past 100,000 years, a field of gas and dust is moving by chance right through the Pleiades star cluster and is causing a strong reaction between the stars and dust. The passing cloud might be part of the Radcliffe wave, a newly discovered structure of gas and dust connecting several regions of star formation in the nearby part of our Milky Way galaxy. Pressure from the stars' light significantly repels the dust in the surrounding blue reflection nebula, with smaller dust particles being repelled more strongly. A short-term result is that parts of the dust cloud have become filamentary and stratified. The featured deep image incorporates nearly 9 hours of exposure and was captured from Utah Desert Remote Observatory in Utah, USA, last year.

APOD: 2024 January 23 – Deep Nebulas: From Seagull to California
Explanation: How well do you know the night sky? OK, but how well can you identify famous sky objects in a very deep image? Either way, here is a test: see if you can find some well-known night-sky icons in a deep image filled with faint nebulosity. This image contains the Pleiades star cluster, Barnard's Loop, Horsehead Nebula, Orion Nebula, Rosette Nebula, Cone Nebula, Rigel, Jellyfish Nebula, Monkey Head Nebula, Flaming Star Nebula, Tadpole Nebula, Aldebaran, Simeis 147, Seagull Nebula and the California Nebula. To find their real locations, here is an annotated image version. The reason this task might be difficult is similar to the reason it is initially hard to identify familiar constellations in a very dark sky: the tapestry of our night sky has an extremely deep hidden complexity. The featured composite reveals some of this complexity in a mosaic of 28 images taken over 800 hours from dark skies over Arizona, USA.

APOD: 2023 December 27 – Rainbow Aurora over Icelandic Waterfall
Explanation: Yes, but can your aurora do this? First, yes, auroras can look like rainbows even though they are completely different phenomena. Auroras are caused by Sun-created particles being channeled into Earth's atmosphere by Earth's magnetic field, and create colors by exciting atoms at different heights. Conversely, rainbows are created by sunlight backscattering off falling raindrops, and different colors are refracted by slightly different angles. Unfortunately, auroras can’t create waterfalls, but if you plan well and are lucky enough, you can photograph them together. The featured picture is composed of several images taken on the same night last November near the Skógafoss waterfall in Iceland. The planning centered on capturing the central band of our Milky Way galaxy over the picturesque cascade. By luck, a spectacular aurora soon appeared just below the curving arch of the Milky Way. Far in the background, the Pleiades star cluster and the Andromeda galaxy can be found.

APOD: 2023 December 19 – NGC 1499: The California Nebula
Explanation: Could Queen Calafia's mythical island exist in space? Perhaps not, but by chance the outline of this molecular space cloud echoes the outline of the state of California, USA. Our Sun has its home within the Milky Way's Orion Arm, only about 1,000 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

APOD: 2023 December 9 - Pic du Pleiades
Explanation: Near dawn on November 19 the Pleiades stood in still dark skies over the French Pyrenees. But just before sunrise a serendipitous moment was captured in this single 3 second exposure; a bright meteor streak appeared to pierce the heart of the galactic star cluster. From the camera's perspective, star cluster and meteor were poised directly above the mountain top observatory on the Pic du Midi de Bigorre. And though astronomers might consider the Pleiades to be relatively close by, the grain of dust vaporizing as it plowed through planet Earth's upper atmosphere actually missed the cluster's tight grouping of young stars by about 400 light-years. While recording a night sky timelapse series, the camera and telephoto lens were fixed to a tripod on the Tour-de-France-cycled slopes of the Col du Tourmalet about 5 kilometers from the Pic du Midi.

APOD: 2023 November 25 - Little Planet Aurora
Explanation: Immersed in an eerie greenish light, this rugged little planet appears to be home to stunning water falls and an impossibly tall mountain. It's planet Earth of course. On the night of November 9 the nadir-centered 360 degree mosaic was captured by digital camera from the Kirkjufell mountain area of western Iceland. Curtains of shimmering Aurora Borealis or Northern Lights provide the pale greenish illumination. The intense auroral display was caused by solar activity that rocked Earth's magnetosphere in early November and produced strong geomagnetic storms. Kirkjufell mountain itself stands at the top of the stereographic projection's circular horizon. Northern hemisphere skygazers will recognize the familiar stars of the Big Dipper just above Kirkjufell's peak. At lower right the compact Pleiades star cluster and truly giant planet Jupiter also shine in this little planet's night sky.

APOD: 2023 October 26 - Orionids in Taurus
Explanation: History's first known periodic comet, Comet Halley (1P/Halley), returns to the inner Solar System every 76 years or so. The famous comet made its last appearance to the naked-eye in 1986. But dusty debris from Comet Halley can be seen raining through planet Earth's skies twice a year during two annual meteor showers, the Eta Aquarids in May and the Orionids in October. In fact, an unhurried series of exposures captured these two bright meteors, vaporizing bits of Halley dust, during the early morning hours of October 23 against a starry background along the Taurus molecular cloud. Impacting the atmosphere at about 66 kilometers per second their greenish streaks point back to the shower's radiant just north of Orion's bright star Betelgeuse off the lower left side of the frame. The familiar Pleiades star cluster anchors the dusty celestial scene at the right.

APOD: 2023 April 15 - When Z is for Mars
Explanation: A composite of images captured about a week apart from mid August 2022 through late March 2023, this series traces the retrograde motion of ruddy-colored Mars. Progressing from lower right to upper left Mars makes a Z-shaped path as it wanders past the Pleiades and Hyades star clusters, through the constellation Taurus in planet Earth's night sky. Seen about every two years, Mars doesn't actually reverse the direction of its orbit to trace out the Z-shape though. Instead, the apparent backwards or retrograde motion with respect to the background stars is a reflection of the orbital motion of Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, the Earth moving more rapidly through its own relatively close-in orbit. High in northern hemisphere skies the Red Planet was opposite the Sun and at its closest and brightest on December 8, near the center of the frame. Seen close to Mars, a popular visitor to the inner Solar System, comet ZTF (C/2022 E3), was also captured on two dates, February 10 and February 16.

APOD: 2023 March 25 - Venus and the Da Vinci Glow
Explanation: On March 23 early evening skygazers could watch Venus and a young crescent moon, both near the western horizon. On that date Earth's brilliant evening star, faint lunar night side and slender sunlit crescent were captured in this telephoto skyscape posing alongside a church tower from San Pietro di Cadore, Dolomiti, Italy. Of course the subtle lunar illumination is earthshine, earthlight reflected from the Moon's night side. A description of earthshine, in terms of sunlight reflected by Earth's oceans illuminating the Moon's dark surface, was written over 500 years ago by Leonardo da Vinci. On March 24, from some locations the Moon could be seen to occult or pass in front of Venus. Around the planet tonight, a waxing lunar crescent will appear near the Pleiades star cluster.

APOD: 2023 March 21 – Dark Nebulae and Star Formation in Taurus
Explanation: Can dust be beautiful? Yes, and it can also be useful. The Taurus molecular cloud has several bright stars, but it is the dark dust that really draws attention. The pervasive dust has waves and ripples and makes picturesque dust bunnies, but perhaps more importantly, it marks regions where interstellar gas is dense enough to gravitationally contract to form stars. In the image center is a light cloud lit by neighboring stars that is home not only to a famous nebula, but to a very young and massive famous star. Both the star, T Tauri, and the nebula, Hind's Variable Nebula, are seen to vary dramatically in brightness -- but not necessarily at the same time, adding to the mystery of this intriguing region. T Tauri and similar stars are now generally recognized to be Sun-like stars that are less than a few million years old and so still in the early stages of formation. The featured image spans about four degrees not far from the Pleiades star cluster, while the featured dust field lies about 400 light-years away.

APOD: 2023 February 27 – Zodiacal Ray with Venus and Jupiter
Explanation: What's causing that unusual ray of light extending from the horizon? Dust orbiting the Sun. At certain times of the year, a band of sun-reflecting dust from the inner Solar System appears prominently after sunset or before sunrise and is called zodiacal light. The dust was emitted mostly from faint Jupiter-family comets and slowly spirals into the Sun. The featured HDR image, acquired in mid-February from the Sierra Nevada National Park in Spain, captures the glowing band of zodiacal light going right in front of the bright evening planets Jupiter (upper) and Venus (lower). Emitted from well behind the zodiacal light is a dark night sky that prominently includes the Pleiades star cluster. Jupiter and Venus are slowly switching places in the evening sky, and just in the next few days nearing their closest angular approach.

APOD: 2023 February 19 – Seven Dusty Sisters in Infrared
Explanation: Is this really the famous Pleiades star cluster? Known for its iconic blue stars, the Pleiades is shown here in infrared light where the surrounding dust outshines the stars. Here three infrared colors have been mapped into visual colors (R=24, G=12, B=4.6 microns). The base images were taken by NASA's orbiting Wide Field Infrared Survey Explorer (WISE) spacecraft. Cataloged as M45 and nicknamed the Seven Sisters, the Pleiades star cluster is by chance situated in a passing dust cloud. The light and winds from the massive Pleiades stars preferentially repel smaller dust particles, causing the dust to become stratified into filaments, as seen. The featured image spans about 20 light years at the distance of the Pleiades, which lies about 450 light years distant toward the constellation of the Bull (Taurus).

APOD: 2023 February 15 – Airglow Sky over France
Explanation: This unusual sky was both familiar and unfamiliar. The photographer's mission was to capture the arch of the familiar central band of our Milky Way Galaxy over a picturesque medieval manor. The surprise was that on this January evening, the foreground sky was found glowing in a beautiful but unfamiliar manner. The striped bands are called airglow and they result from air high in Earth's atmosphere being excited by the Sun's light and emitting a faint light of its own. The bands cross the entire sky -- their curved appearance is due to the extremely wide angle of the camera lens. In the foreground lies Château de Losse in southwest France. Other familiar sky delights dot the distant background including the bright white star Sirius, the orange planet Mars, the blue Pleiades star cluster, the red California Nebula, and, on the far right, the extended Andromeda Galaxy. The initial mission was also successful: across the top of the frame is the arching band of our Milky Way.

APOD: 2023 January 5 - Messier 45: The Daughters of Atlas and Pleione
Explanation: Hurtling through a cosmic dust cloud a mere 400 light-years away, the lovely Pleiades or Seven Sisters open star cluster is well-known for its striking blue reflection nebulae. It lies in the night sky toward the constellation Taurus and the Orion Arm of our Milky Way galaxy. The sister stars are not related to the dusty cloud though. They just happen to be passing through the same region of space. Known since antiquity as a compact grouping of stars, Galileo first sketched the star cluster viewed through his telescope with stars too faint to be seen by eye. Charles Messier recorded the position of the cluster as the 45th entry in his famous catalog of things which are not comets. In Greek myth, the Pleiades were seven daughters of the astronomical titan Atlas and sea-nymph Pleione. Their parents names are included in the cluster's nine brightest stars. This well-processed, color-calibrated telescopic image features pin-point stars and detailed filaments of interstellar dust captured in over 9 hours of exposure. It spans more than 20 light-years across the Pleiades star cluster.

APOD: 2023 January 2 – After Sunset Planet Parade
Explanation: Look up tonight and see a whole bunch of planets. Just after sunset, looking west, planets Venus, Saturn, Jupiter and Mars will all be simultaneously visible. Listed west to east, this planetary lineup will have Venus nearest the horizon, but setting shortly after the Sun. It doesn't matter where on Earth you live because this early evening planet parade will be visible through clear skies all around the globe. Taken late last month, the featured image captured all of these planets and more: the Moon and planet Mercury were also simultaneously visible. Below visibility were the planets Neptune and Uranus, making this a nearly all-planet panorama. In the foreground are hills around the small village of Gökçeören, Kaş, Turkey, near the Mediterranean coast. Bright stars Altair, Fomalhaut, and Aldebaran are also prominent, as well as the Pleiades star cluster. Venus will rise higher in the sky at sunset as January continues, but Saturn will descend.

APOD: 2022 December 30 - Mars and the Star Clusters
Explanation: At this year's end Mars still shines brightly in planet Earth's night as it wanders through the head-strong constellation Taurus. Its bright yellowish hue dominates this starry field of view that includes Taurus' alpha star Aldebaran and the Hyades and Pleiades star clusters. While red giant Aldebaran appears to anchor the V-shape of the Hyades at the left of the frame, Aldebaran is not a member of the Hyades star cluster. The Hyades cluster is 151 light-years away making it the nearest established open star cluster, but Aldebaran lies at less than half that distance, along the same line-of-sight. At the right, some 400 light-years distant is the open star cluster cataloged as Messier 45, also known as the Pleiades or Seven Sisters. In Greek myth, the Pleiades were daughters of the astronomical titan Atlas and sea-nymph Pleione.

APOD: 2022 December 5 - Pleiades: The Seven Sisters Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as large and clear as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen with the unaided eye even from the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured 11-hour exposure, taken from the Siding Spring Observatory in Australia, covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six of the sister stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2022 November 12 - Eclipse in the City
Explanation: A darker Moon sets over Manhattan in this night skyscape. The 16 frame composite was assembled from consecutive exposures recorded during the November 8 total lunar eclipse. In the timelapse sequence stars leave short trails above the urban skyline, while the Moon remains immersed in Earth's shadow. But the International Space Station was just emerging from the shadow into the sunlit portion of its low Earth orbit. As seen from New York City, the visible streak of this ISS flyover starts near a star in Taurus and tracks right to left, through the belt of Orion and over Sirius, alpha star of Canis Major. Gaps along the bright trail of the fast moving orbital outpost (and an aircraft flying closer to the horizon) mark the time between individual exposures in the sequence. The trail of bright planet Mars is at the top of the frame. Pleiades star cluster trails are high over the eclipsed Moon and Empire State Building.

APOD: 2022 October 22 - NGC 1499: The California Nebula
Explanation: Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. The California Nebula shines with the telltale reddish glow characteristic of hydrogen atoms recombining with long lost electrons. The electrons have been stripped away, ionized by energetic starlight. Most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot star Xi Persei just to the right of the nebula. A popular target for astrophotographers, this deep image reveals the glowing nebula, obscuring dust, and stars across a 3 degree wide field of view. The California nebula lies toward the constellation Perseus, not far from the Pleiades.

APOD: 2022 July 19 - Pleiades over Half Dome
Explanation: Stars come in bunches. The most famous bunch of stars on the sky is the Pleiades, a bright cluster that can be easily seen with the unaided eye. The Pleiades lies only about 450 light years away, formed about 100 million years ago, and will likely last about another 250 million years. Our Sun was likely born in a star cluster, but now, being about 4.5 billion years old, its stellar birth companions have long since dispersed. The Pleiades star cluster is pictured over Half Dome, a famous rock structure in Yosemite National Park in California, USA. The featured image is a composite of 28 foreground exposures and 174 images of the stellar background, all taken from the same location and by the same camera on the same night in October 2019. After calculating the timing of a future juxtaposition of the Pleiades and Half Dome, the astrophotrographer was unexpectedly rewarded by an electrical blackout, making the background sky unusually dark.

APOD: 2022 May 3 - Mercury's Sodium Tail
Explanation: That's no comet. Below the Pleiades star cluster is actually a planet: Mercury. Long exposures of our Solar System's innermost planet may reveal something unexpected: a tail. Mercury's thin atmosphere contains small amounts of sodium that glow when excited by light from the Sun. Sunlight also liberates these atoms from Mercury's surface and pushes them away. The yellow glow from sodium, in particular, is relatively bright. Pictured, Mercury and its sodium tail are visible in a deep image taken last week from La Palma, Spain through a filter that primarily transmits yellow light emitted by sodium. First predicted in the 1980s, Mercury's tail was first discovered in 2001. Many tail details were revealed in multiple observations by NASA's robotic MESSENGER spacecraft that orbited Mercury between 2011 and 2015. Tails, of course, are usually associated with comets.

APOD: 2022 April 5 - Seven Sisters versus California
Explanation: On the upper right, dressed in blue, is the Pleiades. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3,000 stars, is about 400 light years away, and only 13 light years across. Surrounding the stars is a spectacular blue reflection nebula made of fine dust. A common legend is that one of the brighter stars faded since the cluster was named. On the lower left, shining in red, is the California Nebula. Named for its shape, the California Nebula is much dimmer and hence harder to see than the Pleiades. Also known as NGC 1499, this mass of red glowing hydrogen gas is about 1,500 light years away. Although about 25 full moons could fit between them, the featured wide angle, deep field image composite has captured them both. A careful inspection of the deep image will also reveal the star forming region IC 348 and the molecular cloud LBN 777 (the Baby Eagle Nebula).

APOD: 2022 March 12 - Point Reyes Milky Way
Explanation: Northern winter constellations and a long arc of the Milky Way are setting in this night skyscape looking toward the Pacific Ocean from Point Reyes on planet Earth's California coast. Sirius, alpha star of Canis Major, is prominent below the starry arc toward the left. Orion's yellowish Betelgeuse, Aldebaran in Taurus, and the blue tinted Pleiades star cluster also find themselves between Milky Way and northwestern horizon near the center of the scene. The nebulae visible in the series of exposures used to construct this panoramic view were captured in early March, but are just too faint to be seen with the unaided eye. On that northern night their expansive glow includes the reddish semi-circle of Barnard's Loop in Orion and NGC 1499 above and right of the Pleiades, also known as the California Nebula.

APOD: 2021 December 4 - Iridescent by Moonlight
Explanation: In this snapshot from November 18, the Full Moon was not far from Earth's shadow. In skies over Sicily the brightest lunar phase was eclipsed by passing clouds though. The full moonlight was dimmed and momentarily diffracted by small but similar sized water droplets near the edges of the high thin clouds. The resulting iridescence shines with colors like a lunar corona. On that night, the Full Moon was also seen close to the Pleiades star cluster appearing at the lower left of the iridescent cloud bank. The stars of the Seven Sisters were soon to share the sky with a darker, reddened lunar disk.

APOD: 2021 November 26 - Great Refractor and Lunar Eclipse
Explanation: Rain clouds passed and the dome of the Lick Observatory's 36 inch Great Refractor opened on November 19. The historic telescope was pointed toward a partially eclipsed Moon. Illuminated by dim red lighting to preserve an astronomer's night vision, telescope controls, coordinate dials, and the refractor's 57 foot long barrel were captured in this high dynamic range image. Visible beyond the foreshortened barrel and dome slit, growing brighter after its almost total eclipse phase, the lunar disk created a colorful corona through lingering clouds. From the open dome, the view of the clearing sky above includes the Pleiades star cluster about 5 degrees from Moon and Earth's shadow.

APOD: 2021 November 24 - Pleiades: The Seven Sisters Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as large and clear as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured exposure, taken from Florida, USA, covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six of the sister stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2021 November 20 - An Almost Total Lunar Eclipse
Explanation: Predawn hours of November 19 found the Moon in partly cloudy skies over Cancun, Mexico. Captured in this telephoto snapshot, the lunar disk is not quite entirely immersed in Earth's dark umbral shadow during a long partial lunar eclipse. The partial eclipse was deep though, deep enough to show the dimmed but reddened light in Earth's shadow. That's a sight often anticipated by fans of total lunar eclipses. Wandering through the constellation Taurus, the eclipsed Moon's dimmer light also made it easier to spot the Pleiades star cluster. The stars of the Seven Sisters share this frame at the upper right, with the almost totally eclipsed Moon.

APOD: 2021 April 6 - Mars and the Pleiades Beyond Vinegar Hill
Explanation: Is this just a lonely tree on an empty hill? To start, perhaps, but look beyond. There, a busy universe may wait to be discovered. First, physically, to the left of the tree, is the planet Mars. The red planet, which is the new home to NASA's Perseverance rover, remains visible this month at sunset above the western horizon. To the tree's right is the Pleiades, a bright cluster of stars dominated by several bright blue stars. The featured picture is a composite of several separate foreground and background images taken within a few hours of each other, early last month, from the same location on Vinegar Hill in Milford, Nova Scotia, Canada. At that time, Mars was passing slowly, night after night, nearly in front of the distant Seven Sisters star cluster. The next time Mars will pass angularly as close to the Pleiades as it did in March will be in 2038.

APOD: 2021 March 11 - Zodiacal Light and Mars
Explanation: Just after sunset on March 7, a faint band of light still reaches above the western horizon in this serene, rural Illinois, night skyscape. Taken from an old farmstead, the luminous glow is zodiacal light, prominent in the west after sunset during planet Earth's northern hemisphere spring. On that clear evening the band of zodiacal light seems to engulf bright yellowish Mars and the Pleiades star cluster. Their close conjunction is in the starry sky above the old barn's roof. Zodiacal light is sunlight scattered by interplanetary dust particles that lie near the Solar System's ecliptic plane. Of course all the Solar System's planets orbit near the plane of the ecliptic, within the band of zodiacal light. But zodiacal light and Mars may have a deeper connection. A recent analysis of serendipitous detections of interplanetary dust by the Juno spacecraft during its Earth to Jupiter voyage suggest Mars is the likely source of the dust that produces zodiacal light.

APOD: 2021 March 10 - NGC 1499: The California Nebula
Explanation: Could Queen Calafia's mythical island exist in space? Perhaps not, but by chance the outline of this molecular space cloud echoes the outline of the state of California, USA. Our Sun has its home within the Milky Way's Orion Arm, only about 1,000 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

APOD: 2021 March 4 - Mars in Taurus
Explanation: You can spot Mars in the evening sky tonight. Now home to the Perseverance rover, the Red Planet is presently wandering through the constellation Taurus, close on the sky to the Seven Sisters or Pleiades star cluster. In fact this deep, widefield view of the region captures Mars near its closest conjunction to the Pleiades on March 3. Below center, Mars is the bright yellowish celestial beacon only about 3 degrees from the pretty blue star cluster. Competing with Mars in color and brightness, Aldebaran is the alpha star of Taurus. The red giant star is toward the lower left edge of the frame, a foreground star along the line-of-sight to the more distant Hyades star cluster. Otherwise too faint for your eye to see, the dark, dusty nebulae lie along the edge of the massive Perseus molecular cloud, with the striking reddish glow of NGC 1499, the California Nebula, at the upper right.

APOD: 2021 January 12 - A Historic Brazilian Constellation
Explanation: The night sky is filled with stories. Cultures throughout history have projected some of their most enduring legends onto the stars above. Generations of people see these stellar constellations, hear the associated stories, and pass them down. Featured here is the perhaps unfamiliar constellation of the Old Man, long recognized by the Tupi peoples native to regions of South America now known as Brazil. The Old Man, in more modern vernacular, may be composed of the Hyades star cluster as his head and the belt of Orion as part of one leg. Tupi folklore relates that the other leg was cut off by his unhappy wife, causing it to end at the orange star now known as Betelgeuse. The Pleiades star cluster, on the far left, can be interpreted as a head feather. In the featured image, the hobbled Old Man is mirrored by a person posing in the foreground. Folklore of the night sky is important for many reasons, including that it records cultural heritage and documents the universality of human intelligence and imagination.

APOD: 2021 January 3 - A Phoenix Aurora over Iceland
Explanation: All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet September night, much of that night's auroras had died down. Suddenly, unexpectedly, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, surprisingly, pareidoliacally, the night lit up with an amazing shape reminiscent of a giant phoenix. With camera equipment at the ready, two quick sky images were taken, followed immediately by a third of the land. The mountain in the background is Helgafell, while the small foreground river is called Kaldá, both located about 30 kilometers north of Iceland's capital Reykjavík. Seasoned skywatchers will note that just above the mountain, toward the left, is the constellation of Orion, while the Pleiades star cluster is also visible just above the frame center. The 2016 aurora, which lasted only a minute and was soon gone forever -- would possibly be dismissed as an fanciful fable -- were it not captured in the featured, digitally-composed, image mosaic.

APOD: 2020 October 13 - Mars, Pleiades, and Andromeda over Stone Lions
Explanation: Three very different -- and very famous -- objects were all captured in a single frame last month. On the upper left is the bright blue Pleiades, perhaps the most famous cluster of stars on the night sky. The Pleiades (M45) is about 450 light years away and easily found a few degrees from Orion. On the upper right is the expansive Andromeda Galaxy, perhaps the most famous galaxy -- external to our own -- on the night sky. Andromeda (M31) is one of few objects visible to the unaided eye where you can see light that is millions of years old. In the middle is bright red Mars, perhaps the most famous planet on the night sky. Today Mars is at opposition, meaning that it is opposite the Sun, with the result that it is visible all night long. In the foreground is an ancient tomb in the Phygrian Valley in Turkey. The tomb, featuring two stone lions, is an impressive remnant of a powerful civilization that lived thousands of years ago. Mars, currently near its brightest, can be easily found toward the east just after sunset.

APOD: 2020 September 9 - Pleiades: The Seven Sisters Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as large and clear as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured exposure covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six of the sister stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2020 July 10 - Comet NEOWISE from the ISS
Explanation: Rounding the Sun on July 3rd and currently headed for the outer Solar System, Comet NEOWISE (C/2020 F3) has been growing brighter in the predawn skies of planet Earth. From low Earth orbit it also rises before the Sun, captured above the approaching glow along the eastern horizon in this snapshot from the International Space Station on July 5. Venus, now Earth's morning star is the brilliant celestial beacon on the right in the field of view. Above Venus you can spot the sister stars of the more compact Pleiades cluster. Earthbound skygazers can spot this comet with the unaided eye, but should look for awesome views with binoculars.

APOD: 2020 April 15 - A Cosmic Triangle
Explanation: It was an astronomical triple play. Setting on the left, just after sunset near the end of last month, was our Moon -- showing a bright crescent phase. Setting on the right was Venus, the brightest planet in the evening sky last month -- and this month, too. With a small telescope, you could tell that Venus' phase was half, meaning that only half of the planet, as visible from Earth, was exposed to direct sunlight and brightly lit. High above and much further in the distance was the Pleiades star cluster. Although the Moon and Venus move with respect to the background stars, the Pleiades do not -- because they are background stars. In the beginning of this month, Venus appeared to move right in front of the Pleiades, a rare event that happens only once every eight years. The featured image captured this cosmic triangle with a series of exposures taken from the same camera over 70 minutes near Avonlea, Saskatchewan, Canada. The positions of the celestial objects was predicted. The only thing unpredicted was the existence of the foreground tree -- and the astrophotographer is still unsure what type of tree that is.

APOD: 2020 April 11 - Venus and the Pleiades in April
Explanation: Shared around world in early April skies Venus, our brilliant evening star, wandered across the face of the lovely Pleiades star cluster. This timelapse image follows the path of the inner planet during the beautiful conjunction showing its daily approach to the stars of the Seven Sisters. From a composite of tracked exposures made with a telephoto lens, the field of view is also appropriate for binocular equipped skygazers. While the star cluster and planet were easily seen with the naked-eye, the spiky appearance of our sister planet in the picture is the result of a diffraction pattern produced by the camera's lens. All images were taken from a home garden in Chiuduno, Bergamo, Lombardy, Italy, fortunate in good weather and clear spring nights.

APOD: 2020 April 6 - NGC 1672: Barred Spiral Galaxy from Hubble
Explanation: Many spiral galaxies have bars across their centers. Even our own Milky Way Galaxy is thought to have a modest central bar. Prominently barred spiral galaxy NGC 1672, featured here, was captured in spectacular detail in an image taken by the orbiting Hubble Space Telescope. Visible are dark filamentary dust lanes, young clusters of bright blue stars, red emission nebulas of glowing hydrogen gas, a long bright bar of stars across the center, and a bright active nucleus that likely houses a supermassive black hole. Light takes about 60 million years to reach us from NGC 1672, which spans about 75,000 light years across. NGC 1672, which appears toward the constellation of the Dolphinfish (Dorado), has been studied to find out how a spiral bar contributes to star formation in a galaxy's central regions.

APOD: 2020 April 5 - Color the Universe
Explanation: Wouldn't it be fun to color in the universe? If you think so, please accept this famous astronomical illustration as a preliminary substitute. You, your friends, your parents or children, can print it out or even color it digitally. While coloring, you might be interested to know that even though this illustration has appeared in numerous places over the past 100 years, the actual artist remains unknown. Furthermore, the work has no accepted name -- can you think of a good one? The illustration, first appearing in a book by Camille Flammarion in 1888, is used frequently to show that humanity's present concepts are susceptible to being supplanted by greater truths.

APOD: 2020 April 4 - Venus and the Sisters
Explanation: After wandering about as far from the Sun on the sky as Venus can get, the brilliant evening star is crossing paths with the sister stars of the Pleiades cluster. Look west after sunset and you can share the ongoing conjunction with skygazers around the world. Taken on April 2, this celestial group photo captures the view from Portal, Arizona, USA. Even bright naked-eye Pleiades stars prove to be much fainter than Venus though. Apparent in deeper telescopic images, the cluster's dusty surroundings and familiar bluish reflection nebulae aren't quite visible, while brighter Venus itself is almost overwhelming in the single exposure. And while Venus and the Sisters do look a little star-crossed, their spiky appearance is the diffraction pattern caused by multiple leaves in the aperture of the telephoto lens. The last similar conjunction of Venus and Pleiades occurred nearly 8 years ago.

APOD: 2020 April 3 - The Traffic in Taurus
Explanation: There's a traffic jam in Taurus lately. On April 1, this celestial frame from slightly hazy skies over Tapiobicske, Hungary recorded an impressive pile up toward the zodiacal constellation of the Bull and the Solar System's ecliptic plane. Streaking right to left the International Space Station speeds across the bottom of the telescopic field of view. Wandering about as far from the Sun in planet Earth's skies as it can get, inner planet Venus is bright and approaching much slower, overexposed at the right. Bystanding at the upper left are the sister stars of the Pleiades. No one has been injured in the close encounter though, because it really isn't very close. Continuously occupied since November 2000, the space station orbits some 400 kilometers above the planet's surface. Venus, currently the brilliant evening star, is almost 2/3 of an astronomical unit away. A more permanent resident of Taurus, the Pleiades star cluster is 400 light-years distant.

APOD: 2020 April 2 - Venus and the Pleiades in April
Explanation: Venus is currently the brilliant evening star. Shared around world, in tonight's sky Venus will begin to wander across the face of the lovely Pleiades star cluster. This digital sky map illustrates the path of the inner planet as the beautiful conjunction evolves, showing its position on the sky over the next few days. The field of view shown is appropriate for binocular equipped skygazers but the star cluster and planet are easily seen with the naked-eye. As viewed from our fair planet, Venus passed in front of the stars of the Seven Sisters 8 years ago, and will again 8 years hence. In fact, orbiting the Sun 13 Venus years are almost equal to 8 years on planet Earth. So we can expect our sister planet to visit nearly the same place in our sky every 8 years.

APOD: 2020 March 23 - From the Pleiades to the Eridanus Loop
Explanation: If you stare at an interesting patch of sky long enough, will it look different? In the case of Pleiades and Hyades star clusters -- and surrounding regions -- the answer is: yes, pretty different. Long duration camera exposures reveal an intricate network of interwoven interstellar dust and gas that was previously invisible not only to the eye but to lower exposure images. In the featured wide and deep mosaic, the dust stands out spectacularly, with the familiar Pleaides star cluster visible as the blue patch near the top of the image. Blue is the color of the Pleiades' most massive stars, whose distinctive light reflects from nearby fine dust. On the upper left is the Hyades star cluster surrounding the bright, orange, foreground-star Aldebaran. Red glowing emission nebula highlight the bottom of the image, including the curving vertical red ribbon known as the Eridanus Loop. The pervasive dust clouds appear typically in light brown and are dotted with unrelated stars.

APOD: 2020 March 7 - Pic du Midi Panorama
Explanation: A surreal night skyscape, this panorama stitched from 12 photos looks to the west at an evening winter sky over Pic du Midi Observatory, Pyrenees Mountains, Planet Earth. Telescope domes and a tall communications tower inhabit the rugged foreground. On the right, lights from Tarbes, France about 35 kilometers away impinge on the designated dark sky site though, but more distant terrestrial lights seen toward the left are from cities in Spain. Stars and nebulae of the northern winter's Milky Way arc through the sky above. Known to the planet's night skygazers, the Pleiades and Hyades star clusters still hang over the western horizon near center. Captured in mid February the familiar stars of the constellation Orion are to the left and include the no longer fainting star Betelgeuse.

APOD: 2020 January 22 - The Hyades Star Cluster
Explanation: It is the closest cluster of stars to the Sun. The Hyades open cluster is bright enough to have been remarked on even thousands of years ago, yet is not as bright or compact as the nearby Pleiades (M45) star cluster. Pictured here is a particularly deep image of the Hyades which has brings out vivid star colors and faint coincidental nebulas. The brightest star in the field is yellow Aldebaran, the eye of the bull toward the constellation of Taurus. Aldebaran, at 65 light-years away, is now known to be unrelated to the Hyades cluster, which lies about 150 light-years away. The central Hyades stars are spread out over about 15 light-years. Formed about 625 million years ago, the Hyades likely shares a common origin with the Beehive cluster (M44), a naked-eye open star cluster toward the constellation of Cancer, based on M44's motion through space and remarkably similar age.

APOD: 2019 December 26 - The Northern Winter Hexagon
Explanation: December's New Moon brought a solar eclipse to some for the holiday season. It also gave beautiful dark night skies to skygazers around the globe, like this moonless northern winter night. In the scene, bright stars of the Winter Hexagon along the Milky Way are rising. Cosy mountain cabins in the snowy foreground are near the village of Oravska Lesna, Slovakia. The shining celestial beacons marking the well-known asterism are Aldebaran, Capella, Pollux (and Castor), Procyon, Rigel, and Sirius. This winter nightscape also reveals faint nebulae in Orion, and the lovely Pleiades star cluster. Slide your cursor over the image to trace the winter hexagon, or just follow this link.

APOD: 2019 December 6 - Pleiades to Hyades
Explanation: This cosmic vista stretches almost 20 degrees from top to bottom, across the dusty constellation Taurus. It begins at the Pleiades and ends at the Hyades, two star clusters recognized since antiquity in Earth's night sky. At top, the compact Pleiades star cluster is about 400 light-years away. The lovely grouping of young cluster stars shine through dusty clouds that scatter blue starlight. At bottom, the V-shaped Hyades cluster looks more spread out in comparison and lies much closer, 150 light-years away. The Hyades cluster stars seem anchored by bright Aldebaran, a red giant star with a yellowish appearance. But Aldebaran actually lies only 65 light-years distant and just by chance along the line of sight to the Hyades cluster. Faint and darkly obscuring dust clouds found near the edge of the Taurus Molecular Cloud are also evident throughout the celestial scene. The wide field of view includes the dark nebula Barnard 22 at left with youthful star T Tauri and Hind's variable nebula just above Aldebaran in the frame.

APOD: 2019 November 7 - Messier 45: The Daughters of Atlas and Pleione
Explanation: Hurtling through a cosmic dust cloud a mere 400 light-years away, the lovely Pleiades or Seven Sisters open star cluster is well-known for its striking blue reflection nebulae. It lies in the night sky toward the constellation Taurus and the Orion Arm of our Milky Way Galaxy. The sister stars and cosmic dust cloud are not related though, they just happen to be passing through the same region of space. Known since antiquity as a compact grouping of stars, Galileo first sketched the star cluster viewed through his telescope with stars too faint to be seen by eye. Charles Messier recorded the position of the cluster as the 45th entry in his famous catalog of things which are not comets. In Greek myth, the Pleiades were seven daughters of the astronomical titan Atlas and sea-nymph Pleione. Their parents names are included in the cluster's nine brightest stars. This deep and wide telescopic image spans over 20 light-years across the Pleides star cluster.

APOD: 2019 September 1 - M45: The Pleiades Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured exposure took over 12 hours and covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2019 August 23 - NGC 1499: The California Nebula
Explanation: Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. The California Nebula shines with the telltale reddish glow characteristic of hydrogen atoms recombining with long lost electrons. The electrons have been stripped away, ionized by energetic starlight. Most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish star Xi Persei just to the right of the nebula. A popular target for astrophotographers, this deep California Nebula image is a 6 panel telecopic mosaic and covers a wide field of view. The nebula lies toward the constellation Perseus, not far from the Pleiades.

APOD: 2019 January 17 - Cabin Under the Stars
Explanation: Gocka's, a family nickname for the mountain cabin, and a wooden sled from a generation past stand quietly under the stars. The single exposure image was taken on January 6 from Tanndalen Sweden to evoke a simple visual experience of the dark mountain skies. A pale band of starlight along the Milky Way sweeps through the scene. At the foot of Orion the Hunter, bright star Rigel shines just above the old kicksled's handrail. Capella, alpha star of Auriga the celestial charioteer, is the brightest star at the top of the frame. In fact, the familiar stars of the winter hexagon and the Pleiades star cluster can all be found in this beautiful skyscape from a northern winter night.

APOD: 2018 December 20 - Red Nebula, Green Comet, Blue Stars
Explanation: This festively colored skyscape was captured in the early morning hours of December 17, following Comet Wirtanen's closest approach to planet Earth. The comet was just visible to the eye. The lovely green color of its fluorescing cometary atmosphere or coma is brought out here only by adding digital exposures registered on the comet's position below the Pleiades star cluster. The exposures also bring out blue starlight reflected by the dust clouds surrounding the young Pleiades stars. Gaze (toward the left) across dusty dark nebulae along the edge of the Perseus molecular cloud and you'll travel to emission nebula NGC 1499, also known as the California nebula. Too faint for the eye, the cosmic cloud's pronounced reddish glow is from electrons recombining with ionized hydrogen atoms. Around December 23rd, Comet Wirtanen should be easy to find with binoculars when it sweeps close to bright star Capella in the northern winter constellation Auriga, the Charioteer.

APOD: 2018 December 15 - Geminids and Friends
Explanation: From a radiant in the constellation of the Twins, the annual Geminid meteor shower rained down on our fair planet this week. This beautiful skyscape collects about 70 of Gemini's lovely shooting stars in a digital composition made from multiple exposures. The exposures were taken over a six hour period near the shower's peak. The camera was tracking the dark predawn sky on December 14 from Teide National Park on the Canary Island Tenerife. Though Gemini lies off the top left of the frame, the Milky Way sweeps through the starry background. Sharing the sky below and left of center are recognizable stars and nebulosities of Orion. A yellowish Aldebaran and the Hyades are toward the right along with the Pleiades star cluster. Also a welcome visitor to this night sky, the faint green coma of Comet 46P Wirtanen, closest to Earth this weekend, lies below the Pleiades stars. Dust swept up from the orbit of active asteroid 3200 Phaethon, Gemini's meteors enter Earth's atmosphere traveling at about 35 kilometers per second.

APOD: 2018 December 7 - December's Comet Wirtanen
Explanation: Coming close in mid-December, Comet 46P Wirtanen hangs in this starry sky over the bell tower of a Romanesque church. In the constructed vertical panorama, a series of digital exposures capture its greenish coma on December 3 from Sant Llorenc de la Muga, Girona, Catalonia, Spain, planet Earth. With an orbital period that is now about 5.4 years, the periodic comet's perihelion, its closest approach, to the Sun will be on December 12. On December 16 it will be closest to Earth, passing at a distance of about 11.6 million kilometers or 39 light-seconds. That's close for a comet, a mere 30 times the Earth-Moon distance. A good binocular target for comet watchers, Wirtanen could be visible to the unaided eye from a dark sky site. To spot it after dusk on December 16, look close on the sky to the Pleiades star cluster in Taurus.

APOD: 2018 November 6 - NGC 1499: The California Nebula
Explanation: There's even a California in space. Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

APOD: 2018 October 19 - Summer to Winter Milky Way
Explanation: Taken near local midnight, this autumn night's panorama follows the arch of the Milky Way across the northern horizon from the High Fens, Eifel Nature Park at the border of Belgium and Germany. Shift your gaze across the wetlands from west to east (left to right) and you can watch stars once more prominent in northern summer give way to those that will soon dominate northern winter nights. Setting, wanderer Mars is brightest at the far left, still shining against almost overwhelming city lights along the southwestern horizon. Bright stars Altair, Deneb, and Vega form the northern sky's summer triangle, straddling the Milky Way left of center. Part of the winter hexagon Capella and Aldebaran, along with the beautiful Pleiades star cluster shine across the northeastern sky. The line-of-sight along the hikers boardwalk leads almost directly toward the Big Dipper, an all season asterism from these northern latitudes. Follow the Big Dipper's pointer stars to Polaris and the north celestial pole nearly centered above it. Andromeda, the other large galaxy in the skyscape, is near the top of the frame.

APOD: 2018 May 28 - Seven Dusty Sisters
Explanation: Is this really the famous Pleaides star cluster? Known for its iconic blue stars, the Pleaides is shown here in infrared light where the surrounding dust outshines the stars. Here three infrared colors have been mapped into visual colors (R=24, G=12, B=4.6 microns). The base images were taken by NASA's orbiting Wide Field Infrared Survey Explorer (WISE) spacecraft. Cataloged as M45 and nicknamed the Seven Sisters, the Pleiades star cluster is by chance situated in a passing dust cloud. The light and winds from the massive Pleiades stars preferentially repels smaller dust particles, causing the dust to become stratified into filaments, as seen. The featured image spans about 20 light years at the distance of the Pleiades, which lies about 450 light years distant toward the constellation of the Bull (Taurus).

APOD: 2018 March 19 - The Nebra Sky Disk
Explanation: Some consider it the oldest known illustration of the night sky. But what, exactly, does it depict, and why was it made? The Nebra sky disk was found with a metal detector in 1999 by treasure hunters near Nebra, Germany, in the midst of several bronze-age weapons. The ancient artifact spans about 30 centimeters and has been associated with the Unetice culture that inhabited part of Europe around 1600 BC. Reconstructed, the dots are thought to represent stars, with the cluster representing the Pleiades, and the large circle and the crescent representing the Sun and Moon. The purpose of the disk remains unknown -- hypotheses including an astronomical clock, a work of art, and a religious symbol. Valued at about $11 million, some believe that the Nebra sky disk is only one of a pair, with the other disk still out there waiting to be discovered.

APOD: 2018 February 16 - Comet PanSTARRS is near the Edge
Explanation: The comet PanSTARRS also known as the blue comet (C/2016 R2) really is near the lower left edge of this stunning, wide field view recorded on January 13. Spanning nearly 20 degrees on the sky, the cosmic landscape is explored by well-exposed and processed frames from a sensitive digital camera. It consists of colorful clouds and dusty dark nebulae otherwise too faint for your eye to see, though. At top right, the California Nebula (aka NGC 1499) does have a familiar shape. Its coastline is over 60 light-years long and lies some 1,500 light-years away. The nebula's pronounced reddish glow is from hydrogen atoms ionized by luminous blue star Xi Persei just below it. Near bottom center, the famous Pleiades star cluster is some 400 light-years distant and around 15 light-years across. Its spectacular blue color is due to the reflection of starlight by interstellar dust. In between are hot stars of the Perseus OB2 association and dusty, dark nebulae along the edge of the nearby, massive Taurus and Perseus molecular clouds. Emission from unusually abundant ionized carbon monoxide (CO+) molecules fluorescing in sunlight is largely responsible for the telltale blue tint of the remarkable comet's tail. The comet was about 17 light minutes from Earth.

APOD: 2018 February 12 - Blue Comet Meets Blue Stars
Explanation: What's that heading for the Pleiades star cluster? It appears to be Comet C/2016 R2 (PanSTARRS), but here, appearances are deceiving. On the right and far in the background, the famous Pleiades star cluster is dominated by blue light from massive young stars. On the left and visiting the inner Solar System is Comet PanSTARRS, a tumbling block of ice from the outer Solar System that currently sports a long ion tail dominated by blue light from an unusually high abundance of ionized carbon monoxide. Comet PanSTARRS is actually moving toward the top of the image, and its ion tail points away from the Sun but is affected by a complex solar wind of particles streaming out from the Sun. Visible through a small telescope, the comet is fading as it recedes from the Earth, even though it reaches its closest point to the Sun in early May.

APOD: 2017 December 9 - Stardust in Aries
Explanation: This composition in stardust covers over 8 degrees on the northern sky. The mosaicked field of view is west of the familiar Pleiades star cluster, toward the zodiacal constellation Aries and the plane of our Milky Way Galaxy. At right in the deep skyscape is bluish Epsilon Arietis, a star visible to the naked-eye and about 330 light-years away. Reflecting starlight in the region, dusty nebulae LBN762, LBN753, and LBN743 sprawl left to right across the field, but are likely some 1,000 light-years away. At that estimated distance, the cosmic canvas is over 140 light-years across. Near the edge of a large molecular cloud, their dark interiors can hide newly formed stars and young stellar objects or protostars from prying optical telescopes. Collapsing due to self-gravity, the protostars form around dense cores embedded in the molecular cloud.

APOD: 2017 November 14 - The Pleiades Deep and Dusty
Explanation: The well-known Pleiades star cluster is slowly destroying part of a passing cloud of gas and dust. The Pleiades is the brightest open cluster of stars on Earth's sky and can be seen from almost any northerly location with the unaided eye. The passing young dust cloud is thought to be part of Gould's Belt, an unusual ring of young star formation surrounding the Sun in the local Milky Way Galaxy. Over the past 100,000 years, part of Gould's Belt is by chance moving right through the older Pleiades and is causing a strong reaction between stars and dust. Pressure from the stars' light significantly repels the dust in the surrounding blue reflection nebula, with smaller dust particles being repelled more strongly. A short-term result is that parts of the dust cloud have become filamentary and stratified. The featured deep image also captured Comet C/2015 ER61 (PanSTARRS) on the lower left.

APOD: 2017 October 2 - Two Comets and a Star Cluster
Explanation: Two unusual spots are on the move near the famous Pleiades star cluster. Shifting only a small amount per night, these spots are actually comets in our nearby Solar System that by chance wandered into the field of the light-years distant stars. On the far left is comet C/2017 O1 ASAS-SN, a multi-kilometer block of evaporating ice sporting a bright coma of surrounding gas dominated by green-glowing carbon. Comet ASAS-SN1 shows a slight tail to its lower right. Near the frame center is comet C/2015 ER61 PanSTARRS, also a giant block of evaporating ice, but sporting a rather long tail to its right. On the upper right is the Pleiades, an open cluster dominated by bright blue stars illuminating nearby reflecting dust. This exposure, taken about two weeks ago, is so deep that the filamentary interstellar dust can be traced across the entire field. The Pleiades is visible to the unaided eye, but it should require binoculars to see the comets.

APOD: 2017 September 23 - A Conjunction of Comets
Explanation: A conjunction of comets is captured in this pretty star field from the morning of September 17. Discovered in July by a robotic sky survey searching for supernovae, comet C/2017 O1 ASASSN is at the lower left. The visible greenish glow of its coma is produced by the fluorescence of diatomic carbon molecules in sunlight. Nearing its closest approach to the Sun, the binocular comet was only about 7.2 light-minutes from Earth. In the same telescopic field of view is the long-tailed, outbound comet C/2015 ER61 PanSTARRS at the upper right, almost 14 light-minutes away. Many light-years distant, the starry background includes faint, dusty nebulae of the Milky Way. The well-known Pleiades star cluster lies just off the top right of the frame.

APOD: 2017 May 30 - A Kalahari Sky
Explanation: You wake up in the Kalahari Desert in Botswana, Africa. You go outside your tent, set up your camera, and take long exposures of the land and sky. What might you see? Besides a lot of blowing dust and the occasional acacia tree, you might catch many sky wonders. Pictured in 2015 September, sky highlights include the central band of our Milky Way Galaxy, the Pleiades Star Cluster, Barnard's Loop, and both the Large and Small Magellanic Clouds, to name just a few. Although most of these faded in the morning light, they were quickly replaced by a partial eclipse of the Sun.

APOD: 2017 May 22 - A Zodiacal Sky over Horseshoe Bend
Explanation: What's causing the unusual ray of white light extending upward from the central horizon? Dust orbiting the Sun. At certain times of the year, a band of sun-reflecting dust from the inner Solar System rises prominently before sunrise and is called zodiacal light. The dust originates mostly from faint Jupiter-family comets and slowly spirals into the Sun. Pictured, in front of the zodiacal light, is a spectacular view of Horseshoe Bend of the Colorado River. Emitted from well behind the zodiacal light is a spectacular sky that includes many bright stars including Sirius, several blue star clusters including the Pleiades, and an assortment of red nebulas including Barnard's Loop in Orion. The 30-image composite was taken earlier this month in nearly complete darkness only six inches from the edge of a dangerous cliff.

APOD: 2017 March 14 - A Dark Winter Sky over Monfragüe National Park in Spain
Explanation: You, too, can see a night sky like this. That is because Monfragüe National Park in Spain, where this composite image was created, has recently had its night sky officially protected from potential future light pollution. Icons of the night sky that should continue to stand out during northern winter -- and are visible on the featured image -- include very bright stars like Sirius, Betelgeuse, and Procyon, bright star clusters like the Pleiades, and, photographically, faint nebulas like the California and Rosette Nebulas. Even 100 years ago, many people were more familiar with a darker night sky than people today, primarily because of the modern light pollution. Other parks that have been similarly protected as dark-sky preserves include Death Valley National Park (USA) and Grasslands National Park (Canada). Areas such as the city of Flagstaff, Arizona and much of the Big Island of Hawaii also have their night skies protected.

APOD: 2017 March 6 - Colorful Aurora over Iceland
Explanation: You don't always see a scene this beautiful when you hike to an ancient volcano -- you have to be lucky. When the astrophotographer realized that auroras were visible two-weeks ago, he made a night-time run for the top of the caldera to see if he could capture them also reflected in the central lake. When he arrived, he found that ... the northern lights were even brighter and more impressive than before! And his image of them is the featured 13-frame panoramic mosaic. The crater lake in the center is called Kerid (Icelandic: Kerið) and is about 3,000 years old. The aurora overhead shows impressive colors and banding, with the red colors occurring higher in the Earth's atmosphere than the green. The background sky is filled with icons of the northern night including Polaris, the Pleiades star cluster, and the stars that compose the handle of the Big Dipper.

APOD: 2017 January 23 - Winter Hexagon over Manla Reservoir
Explanation: If you can find Orion, you might be able to find the Winter Hexagon. The Winter Hexagon involves some of the brightest stars visible, together forming a large and easily found pattern in the winter sky of Earth's northern hemisphere. The stars involved can usually be identified even in the bright night skies of a big city, although here they appeared recently in dark skies above the Manla Reservoir in Tibet, China. The six stars that compose the Winter Hexagon are Aldebaran, Capella, Castor (and Pollux), Procyon, Rigel, and Sirius. Here, the band of our Milky Way Galaxy runs through the center of the Winter Hexagon, while the Pleiades open star cluster is visible just above. The Winter Hexagon asterism engulfs several constellations including much of the iconic steppingstone Orion.

APOD: 2016 October 19 - M45: The Pleiades Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars even from the heart of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured image was a long duration exposure taken last month from Namibia and covers a sky area many times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of visible Pleiades stars, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2016 August 18 - Perseid Night at Yosemite
Explanation: The 2016 Perseid meteor shower performed well on the night of August 11/12. The sky on that memorable evening was recorded from a perch overlooking Yosemite Valley, planet Earth, in this scene composed of 25 separate images selected from an all-night set of sequential exposures. Each image contains a single meteor and was placed in alignment using the background stars. The digital manipulation accounts for the Earth's rotation throughout the night and allows the explosion of colorful trails to be viewed in perspective toward the shower's radiant in the constellation Perseus. The fading alpenglow gently lights the west face of El Capitan just after sunset. Just before sunrise, a faint band zodiacal light, or the false dawn, shines upward from the east, left of Half Dome at the valley's far horizon. Car lights illuminate the valley road. Of course, the image is filled with other celestial sights from that Perseid night, including the Milky Way and the Pleiades star cluster.

APOD: 2016 March 14 - Dark Nebulas across Taurus
Explanation: Sometimes even the dark dust of interstellar space has a serene beauty. One such place occurs toward the constellation of Taurus. The filaments featured here can be found on the sky between the Pleiades star cluster and the California Nebula. This dust is not known not for its bright glow but for its absorption and opaqueness. Several bright stars are visible with their blue light seen reflecting off the brown dust. Other stars appear unusually red as their light barely peaks through a column of dark dust, with red the color that remains after the blue is scattered away. Yet other stars are behind dust pillars so thick they are not visible here. Although appearing serene, the scene is actually an ongoing loop of tumult and rebirth. This is because massive enough knots of gas and dust will gravitationally collapse to form new stars -- stars that both create new dust in their atmospheres and destroy old dust with their energetic light and winds.

APOD: 2016 January 12 - The California Nebula
Explanation: What's California doing in space? Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

APOD: 2015 November 3 - Seeking Venus under the Spitzkoppe Arch
Explanation: What's that in the sky? Although there was much to see in this spectacular panorama taken during the early morning hours of a day in late September, the brightest object in the sky was clearly the planet Venus. In the featured image, Venus was captured actually through a natural rock bridge, itself picturesque, in Spitzkoppe, Namibia. The planet, on the left of the opening, was complemented by a silhouette of the astrophotographer on the right. Above and beyond the rock bridge were many famous icons of a dark night sky, including, from left to right, the Pleiades star cluster, the Orion Nebula, the bright star Sirius, and the Large and Small Magellanic Clouds. This week, Venus remains visible to the east in the pre-dawn sky, being complemented by Mars, which is angularly quite close.

APOD: 2015 June 17 - M45: The Pleiades Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured exposure took over 12 hours and covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2015 April 11 - Venus in the West
Explanation: In the coming days, Venus shines near the western horizon at sunset. To find Earth's sister planet in twilight skies just look for the brilliant evening star. Tonight very close to the Pleiades star cluster, Venus dominates this springtime night skyscape taken only a few days ago near the town of Lich in central Germany. Also known as the Seven Sisters, the stars of the compact Pleiades cluster appear above Venus in this picture. The budding tree branches to its left frame bright star Aldebaran, the eye of Taurus the Bull, and the V-shaped Hyades star cluster.

APOD: 2015 January 28 - Comet Lovejoy in a Winter Sky
Explanation: Which of these night sky icons can you find in this beautiful and deep exposure of the northern winter sky? Skylights include the stars in Orion's belt, the Orion Nebula, the Pleiades star cluster, the bright stars Betelgeuse and Rigel, the California Nebula, Barnard's Loop, and Comet Lovejoy. The belt stars of Orion are nearly vertical in the central line between the horizon and the image center, with the lowest belt star obscured by the red glowing Flame Nebula. To the belt's left is the red arc of Barnard's Loop followed by the bright orange star Betelgeuse, while to the belt's right is the colorful Orion Nebula followed by the bright blue star Rigel. The blue cluster of bright stars near the top center is the Pleiades, and the red nebula to its left is the California nebula. The bright orange dot above the image center is the star Aldebaran, while the green object with the long tail to its right is Comet C/2014 Q2 (Lovejoy). The featured image was taken about two weeks ago near Palau village in Spain.

APOD: 2015 January 22 - Launch to Lovejoy
Explanation: Blasting skyward an Atlas V rocket carrying a U.S. Navy satellite pierces a cloud bank in this starry night scene captured on January 20. On its way to orbit from Space Launch Complex 41, Cape Canaveral Air Force Station, planet Earth, the rocket streaks past brightest star Sirius, as seen from a dark beach at Canaveral National Seashore. Above the alpha star of Canis Major, Orion the Hunter strikes a pose familiar to northern winter skygazers. Above Orion is the V-shaped Hyades star cluster, head of Taurus the Bull, and farther still above Taurus it's easy to spot the compact Pleiades star cluster. Of course near the top of the frame you'll find the greenish coma and long tail of Comet Lovejoy, astronomical darling of these January nights.

APOD: 2014 September 11 - Zodiacal Light before Dawn
Explanation: You might not guess it, but sunrise was still hours away when this nightscape was taken, a view along the eastern horizon from a remote location in Chile's Atacama desert. Stretching high into the otherwise dark, starry sky the unusually bright conical glow is sunlight though, scattered by dust along the solar system's ecliptic plane . Known as Zodiacal light, the apparition is also nicknamed the "false dawn". Near center, bright star Aldebaran and the Pleiades star cluster seem immersed in the Zodiacal light, with Orion toward the right edge of the frame. Reddish emission from NGC 1499, the California Nebula, can also be seen through the tinge of airglow along the horizon. Sliding your cursor over the picture (or following this link) will label the sky over this future site of the Giant Magellan Telescope at Las Campanas Observatory.

APOD: 2014 April 28 - Time Lapse of a Total Lunar Eclipse
Explanation: Why would a bright full Moon suddenly become dark? Because it entered the shadow of the Earth. Almost two weeks ago this exact event happened as the Moon underwent a total lunar eclipse. That eclipse, visible from the half of the Earth then facing the Moon, was captured in numerous spectacular photographs and is depicted in the above time lapse video covering about an hour. The above video, recorded from Mt. Lemmon Sky Center in Arizona, USA, keeps the Earth shadow centered and shows the Moon moving through it from west to east. The temporarily good alignment between Earth, Moon, and Sun will show itself again tomorrow -- precisely half a moon-th (month) later -- when part of the Earth will pass through part of the new Moon's shadow.

APOD: 2014 February 25 - The Pleiades Deep and Dusty
Explanation: The well known Pleiades star cluster is slowly destroying part of a passing cloud of gas and dust. The Pleiades is the brightest open cluster of stars on Earth's sky and can be seen from almost any northerly location with the unaided eye. The passing young dust cloud is thought to be part of Gould's belt, an unusual ring of young star formation surrounding the Sun in the local Milky Way Galaxy. Over the past 100,000 years, part of Gould's belt is by chance moving right through the older Pleiades and is causing a strong reaction between stars and dust. Pressure from the stars' light significantly repels the dust in the surrounding blue reflection nebula, with smaller dust particles being repelled more strongly. A short-term result is that parts of the dust cloud have become filamentary and stratified, as seen in the above deep-exposure image.

APOD: 2014 January 14 - The Gegenschein Over Chile
Explanation: Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets. Pictured above from last year is one of the more spectacular pictures of the gegenschein yet taken. Here a deep exposure of an extremely dark sky over Las Campanas Observatory in Chile shows the gegenschein so clearly that even a surrounding glow is visible. Notable background objects include the Andromeda galaxy, the Pleiades star cluster, the California Nebula, the belt of Orion just below the Orion Nebula and inside Barnard's Loop, and bright stars Rigel and Betelgeuse. The gegenschein is distinguished from zodiacal light near the Sun by the high angle of reflection. During the day, a phenomenon similar to the gegenschein called the glory can be seen in reflecting air or clouds opposite the Sun from an airplane.

APOD: 2013 November 22 - From California to the Pleiades
Explanation: An astronomical trip from the California Nebula to the Pleiades star cluster would cover just over 12 degrees across planet Earth's night sky. That's equivalent to the angular extent of 25 Full Moons, as your telescope sweeps past the borders of the constellations Perseus and Taurus. This wide and deep mosaic image of the region explores the cosmic landscape's dusty nebulae and colors otherwise too faint for your eye to see. On the left, cataloged as NGC 1499, the California Nebula does have a familiar shape, though its coastline is actually over 60 light-years long and lies about 1,500 light-years away. The nebula's pronounced reddish glow is from hydrogen atoms ionized by luminous blue star Xi Persei seen just to its right. At the far right, the famous Pleiades star cluster is some 400 light-years distant and around 15 light-years across. Its spectacular blue color is due to the reflection of starlight by interstellar dust. In between are hot stars of the Perseus OB2 association and dusty, dark nebulae along the edge of the nearby, massive Perseus molecular cloud.

APOD: 2013 September 18 - M45: The Pleiades Star Cluster
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The above exposure took about 20 minutes and covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2013 February 12 - Reflected Aurora Over Alaska
Explanation: Some auroras can only be seen with a camera. They are called subvisual and are too faint to be seen with the unaided eye. In the above image, the green aurora were easily visible to the eye, but the red aurora only became apparent after a 20-second camera exposure. The reason is that the human eye only accumulates light for a fraction of a second at a time, while a camera shutter can be left open much longer. When photographing an already picturesque scene near Anchorage, Alaska, USA, last autumn, a camera caught both the visual green and subvisual red aurora reflected in a lily pad-covered lake. High above, thousands of stars were visible including the Pleiades star cluster, while the planet Jupiter posed near the horizon, just above clouds, toward the image right. Auroras are caused by energetic particles from the Sun impacting the Earth's magnetosphere, causing electrons and protons to rain down near the Earth's poles and impact the air. Both red and green aurora are typically created by excited oxygen atoms, with red emission, when visible, dominating higher up. Auroras are known to have many shapes and colors.

APOD: 2012 December 2 - The Gegenschein Over Chile
Explanation: Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets. Pictured above from 2008 October is one of the more spectacular pictures of the gegenschein yet taken. Here a deep exposure of an extremely dark sky over Paranal Observatory in Chile shows the gegenschein so clearly that even a surrounding glow is visible. In the foreground are several of the European Southern Observatory's Very Large Telescopes, while notable background objects include the Andromeda galaxy toward the lower left and the Pleiades star cluster just above the horizon. The gegenschein is distinguished from zodiacal light near the Sun by the high angle of reflection. During the day, a phenomenon similar to the gegenschein called the glory can be seen in reflecting air or clouds opposite the Sun from an airplane.

APOD: 2012 November 27 - Bright Jupiter in Taurus
Explanation: That bright star you've recently noticed rising just after sunset isn't a star at all. It's Jupiter, the solar system's ruling gas giant. Bright Jupiter is nearing its December 3rd opposition when it will stand in Taurus, opposite the Sun in planet Earth's sky. Clearly outshining yellowish Aldebaran, alpha star of Taurus, Jupiter is centered in this skyview from November 14th, also featuring the Pleiades and Hyades star clusters, familiar celestial sights as the northern hemisphere winter approaches. Sliding your cursor over the image will label the scene and identify two other solar system worlds approaching their opposition in December. Small and faint, asteroid Vesta and dwarf planet Ceres are about 10 degrees from Jupiter, near the left edge of the frame. Of course, you can imagine NASA's Dawn spacecraft in this field of view. Having left Vesta in September, Dawn's ion engine is now steadily driving it to match orbits with Ceres, scheduled to arrive there in February 2015.

APOD: 2012 October 26 - Reflection Nebula vdB1
Explanation: Every book has a first page and every catalog a first entry. And so this lovely blue cosmic cloud begins the van den Bergh Catalog (vdB) of stars surrounded by reflection nebulae. Interstellar dust clouds reflecting the light of the nearby stars, the nebulae usually appear blue because scattering by the dust grains is more effective at shorter (bluer) wavelengths. The same type of scattering gives planet Earth its blue daytime skies. Van den Bergh's 1966 list contains a total of 158 entries more easily visible from the northern hemisphere, including bright Pleiades cluster stars and other popular targets for astroimagers. Less than 5 light-years across, VdB1 lies about 1,600 light-years distant in the constellation Cassiopeia. Also on this scene, two intriguing nebulae at the right show loops and outflow features associated with the energetic process of star formation. Within are extremely young variable stars V633 Cas (top) and V376 Cas.

APOD: 2012 October 20 - Zodiacal Light and Milky Way
Explanation: Ghostly apparitions of two fundamental planes in planet Earth's sky span this October all-sky view. The scene was captured from a lakeside campsite under dark skies in northern Maine, USA. In it, the plane of our Milky Way Galaxy arcs above faint airglow along the horizon. Zodiacal light, a band of dust scattering sunlight along the solar system's ecliptic plane, stretches almost horizontally across the wide field and intersects the Milky way near a point marked by bright planet Jupiter. Right of Jupiter, past the Pleiades star cluster, is the brightening of the Zodiacal band known as the Gegenschein, also visible to the eye on that dark night. Begirt with many a blazing star and rising above the distant mountains, Orion the hunter is reflected in the lake's calm waters.

APOD: 2012 September 3 - M45: The Pleiades Star Cluster
Explanation: Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades. (Editors' note: The prominent diffraction spikes are caused by the telescope itself and may be either distracting or provide aesthetic enhancement, depending on your point of view.)

APOD: 2012 July 19 - Dawn of the Dish
Explanation: Wandering planets Venus and Jupiter were joined by an old crescent Moon near the eastern horizon on July 15. This serene southern skyview of the much anticipated predawn conjunction includes the lovely Pleiades star cluster and bright stars Aldebaran and Betelgeuse in the celestial lineup. For help identifying the stars and constellations, just slide your cursor over the image. Of course, the radio telescope in the foreground is the Parkes 64 meter dish of New South Wales, Australia. Known for its exploration of the distant Universe at radio wavelengths, the large, steerable antenna is also famous for its superior lunar television reception. On July 21, 1969 the dish received broadcasts from the Moon that allowed denizens of planet Earth to watch the Apollo 11 moonwalk.

APOD: 2012 July 11 - A Morning Line of Stars and Planets
Explanation: Early morning dog walkers got a visual treat last week as bright stars and planets appeared to line up. Pictured above, easily visible from left to right, were the Pleiades open star cluster, Jupiter, Venus, and the "Follower" star Aldebaran, all seen before a starry background. The image was taken from the Atacama desert in western South America. The glow of the rising Sun can be seen over the eastern horizon. Jupiter and Venus will continue to dazzle pre-dawn strollers all over planet Earth for the rest of the month, although even now the morning planets are seen projected away from the line connecting their distant stellar sky mates.

APOD: 2012 June 30 - Conjunctions near Dawn
Explanation: Now shining in eastern skies at dawn, bright planets Venus and Jupiter join the Pleiades star cluster in this sea and sky scape, recorded earlier this week near Buenos Aires, Argentina. Venus dominates the scene that includes bright star Aldebaran just below and to the right. The planets are easy to spot for early morning risers, but this sky also holds two of our solar system's small worlds, Vesta and Ceres, not quite bright enough to be seen with the unaided eye. The digital camera's time exposure just captures them, though. Their positions are indicated when you put your cursor over the image. In orbit around Vesta, NASA's Dawn spacecraft arrived there last July, but is nearing the end of its visit to the main belt asteroid. In August, it will set off on its planned journey to Ceres, arriving at the dwarf planet in 2015.

APOD: 2012 April 12 - Yuri's Planet
Explanation: On another April 12th, in 1961, Soviet cosmonaut Yuri Alexseyevich Gagarin became the first human to see planet Earth from space. Commenting on his view from orbit he reported, "The sky is very dark; the Earth is bluish. Everything is seen very clearly". To celebrate, consider this recent image from the orbiting International Space Station. A stunning view of the planet at night from an altitude of 240 miles, it was recorded on March 28. The lights of Moscow, Russia are near picture center and one of the station's solar panel arrays is on the left. Aurora and the glare of sunlight lie along the planet's gently curving horizon. Stars above the horizon include the compact Pleiades star cluster, immersed in the auroral glow.

APOD: 2012 April 7 - Conjunction Haiku
Explanation:

APOD: 2012 April 6 - Venus and the Sisters
Explanation: After wandering about as far from the Sun on the sky as Venus can get, the brilliant evening star crossed paths with the Pleiades star cluster earlier this week. The beautiful conjunction was enjoyed by skygazers around the world. Taken on April 2, this celestial group photo captures the view from Portal, Arizona, USA. Also known as the Seven Sisters, even the brighter naked-eye Pleiades stars are seen to be much fainter than Venus. And while Venus and the sisters do look star-crossed, their spiky appearance is the diffraction pattern caused by multiple leaves in the aperture of the telephoto lens. The last similar conjunction of Venus and Pleiades occurred nearly 8 years ago. As it did then, Venus will again move on to cross paths with the disk of the Sun in June.

APOD: 2012 March 30 - The Grand Canyon in Moonlight
Explanation: In this alluring night skyscape recorded on March 26, a young Moon stands over the distant western horizon in conjunction with brilliant planet Venus. In the foreground, the Colorado River glistens in moonlight as it winds through the Grand Canyon, seen from the canyon's southern rim at Lipan Point. Of course, the Grand Canyon is known as one of the wonders of planet Earth. Carved by the river, the enormous fissure is about 270 miles (440 kilometers) long, up to 18 miles (30 kilometers) wide and approaches 1 mile (1.6 kilometers) deep. On this date, wonders of the night sky included the compact Pleiades and V-shaped Hyades star clusters poised just above the Moon. Bright planet Jupiter is below the closer Moon/Venus pairing, near the western horizon.

APOD: 2012 March 16 - Bright Planets at McMath-Pierce Solar Telescope
Explanation: Bright planets Venus and Jupiter are framed by the National Solar Observatory's McMath-Pierce Solar Telescope in this very astronomical scene. The photo was taken at Kitt Peak National Observatory on March 9. A heliostat sits atop the 100 foot high solar telescope tower to focus the Sun's rays down a long diagonal shaft that reaches underground to the telescope's primary mirror. Of course, after sunset shadows were cast and the structure illuminated by light from the nearly full rising Moon. Opened to begin the night's work, the dome housing Kitt Peak's 2.1 meter reflector is included in the frame, while the Pleiades star cluster shines above the heliostat tower. The angular McMath-Pierce was commissioned 50 years ago to study the Sun, but has also made many observations of these two bright planets. On this night it was conducting observations of sodium atoms in the tenuous lunar atmosphere.

APOD: 2012 February 15 - Meropes Reflection Nebula
Explanation: Reflection nebulas reflect light from a nearby star. Many small carbon grains in the nebula reflect the light. The blue color typical of reflection nebula is caused by blue light being more efficiently scattered by the carbon dust than red light. The brightness of the nebula is determined by the size and density of the reflecting grains, and by the color and brightness of the neighboring star(s). NGC 1435, pictured above, surrounds Merope (23 Tau), one of the brightest stars in the Pleiades (M45). The Pleiades nebulosity is caused by a chance encounter between an open cluster of stars and a dusty molecular cloud.

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 28 - Planet Aurora Borealis
Explanation: Illuminated by an eerie greenish light, this remarkable little planet is covered with ice and snow and ringed by tall pine trees. Of course, this little planet is actually planet Earth, and the surrounding stars are above the horizon near Östersund, Sweden. The pale greenish illumination is from a curtain of shimmering Aurora Borealis also known as the Northern Lights. The display was triggered when a giant solar coronal mass ejection (CME) rocked planet Earth's magnetosphere on January 24th and produced a strong geomagnetic storm. Northern hemisphere skygazers will also recognize the familiar orientation of stars at the left, including the Pleiades and Hyades star clusters and the stars of Orion. Increasing solar activity has caused recent auroral displays to be wide spread, including Aurora Australis, the Southern Lights, at high southern latitudes.

APOD: 2011 November 17 - Pleiades to Hyades
Explanation: This cosmic vista stretches almost 20 degrees across the gentle constellation Taurus. It begins at the Pleiades and ends at the Hyades, two of the best known star clusters in planet Earth's sky. At left, the lovely Pleiades star cluster is about 400 light-years away. In a familiar celestial scene, the cluster stars shine through dusty clouds that scatter blue starlight. At right, the V-shaped Hyades cluster looks more spread out compared to the compact Pleiades and lies much closer, 150 light-years distant. Of course, the Hyades cluster stars seem anchored by bright Aldebaran, a red giant star with a yellowish appearance. But Aldebaran actually lies only 65 light-years away, by chance along the line of sight to the Hyades cluster. Faint dust clouds found near the edge of the Taurus Molecular Cloud are also evident throughout the remarkable 12 panel mosaic. The wide field of view includes the youthful star T Tauri and Hind's variable nebula about four degrees left of Aldebaran on the sky.

APOD: 2011 October 3 - Dark Matter Movie from the Bolshoi Simulation
Explanation: What if you could fly through the universe and see dark matter? While the technology for taking such a flight remains under development, the technology for visualizing such a flight has taken a grand leap forward with the completion of the Bolshoi Cosmological Simulation. After 6 million CPU hours, the world's seventh fastest supercomputer output many scientific novelties including the above flight simulation. Starting from the relatively smooth dark matter distribution of the early universe discerned from the microwave background and other large sky data sets, the Bolshoi tracked the universe's evolution to the present epoch shown above, given the standard concordance cosmology. The bright spots in the above video are all knots of normally invisible dark matter, many of which contain normal galaxies. Long filaments and clusters of galaxies, all gravitationally dominated by dark matter, become evident. Statistical comparison between the Bolshoi and current real sky maps of actual galaxies show good agreement. Although the Bolshoi simulation bolsters the existence of dark matter, many questions about our universe remain, including the composition of dark matter, the nature of dark energy, and how the first generation of stars and galaxies formed.

APOD: 2011 September 30 - Cloudy Night of the Northern Lights
Explanation: On September 26, a large solar coronal mass ejection smacked into planet Earth's magnetosphere producing a severe geomagnetic storm and wide spread auroras. Captured here near local midnight from Kvaløya island outside Tromsø in northern Norway, the intense auroral glow was framed by parting rain clouds. Tinted orange, the clouds are also in silhouette as the tops of the colorful shimmering curtains of northern lights extend well over 100 kilometers above the ground. Though the auroral rays are parallel, perspective makes them appear to radiate from a vanishing point at the zenith. Near the bottom of the scene, an even more distant Pleiades star cluster and bright planet Jupiter shine on this cloudy northern night.

APOD: 2011 September 21 - Pleiades Deep Field
Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it like this: all dusty. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The above exposure took about 30 hours and covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

APOD: 2011 August 13 - Castle and Meteor by Moonlight
Explanation: Each August, as planet Earth swings through dust trailing along the orbit of periodic comet Swift-Tuttle, skygazers enjoy the Perseid Meteor Shower. As Earth moves through the denser part of the comet's wide dust trail this year's shower peaks around 6:00 UT August 13 (this morning), when light from a nearly full Moon masks all but the brighter meteor streaks. Still, Perseid meteors can be spotted in the days surrounding the peak. Moonlight and a Perseid meteor created this gorgeous skyscape, recorded in a simple, single, 10 second long exposure on the morning of August 12. Below the moonlit clouds in the foreground are the ruins of a medieval castle near Veszprem, Hungary, seen against the Bakony mountain range. In the night sky above the clouds, the Perseid meteor's trail is joined by bright planet Jupiter near the center of the frame along with the lovely Pleiades star cluster at the left.

APOD: 2011 May 17 - A Starry Night of Iceland
Explanation: On some nights, the sky is the best show in town. On this night, the sky was not only the best show in town, but a composite image of the sky won an international competition for landscape astrophotography. The above winning image was taken two months ago over Jökulsárlón, the largest glacial lake in Iceland. The photographer combined six exposures to capture not only two green auroral rings, but their reflections off the serene lake. Visible in the distant background sky is the band of our Milky Way Galaxy, the Pleiades open clusters of stars, and the Andromeda galaxy. A powerful coronal mass ejection from the Sun caused auroras to be seen as far south as Wisconsin, USA. As the Sun progresses toward solar maximum in the next few years, many more spectacular images of aurora are expected.

APOD: 2011 March 2 - NGC 1499: The California Nebula
Explanation: What's California doing in space? Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On many images, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. In the above image, however, hydrogen is colored green, while sulfur is mapped to red and oxygen mapped to blue. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei, just outside the right image edge. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

APOD: 2011 January 3 - Winter Hexagon Over Stagecoach Colorado
Explanation: If you can find Orion, you might be able to find the Winter Hexagon. The Winter Hexagon involves some of the brightest stars visible, together forming a large and easily found pattern in the winter sky of Earth's northern hemisphere. The stars involved can usually be identified even in the bright night skies of a big city, although here they appear over darker Stagecoach, Colorado, USA.. The six stars that compose the Winter Hexagon are Aldebaran, Capella, Castor (and Pollux), Procyon, Rigel, and Sirius. Here, the band of our Milky Way Galaxy runs through the center of the Winter Hexagon, while the Pleiades open star cluster is visible just above. The Winter Hexagon asterism engulfs several constellations including much of the iconic steppingstone Orion.

APOD: 2010 November 18 - Sisters of the Dusty Sky
Explanation: Hurtling through a cosmic dust cloud some 400 light-years away, the lovely Pleiades or Seven Sisters star cluster is well-known for its striking blue reflection nebulae. In the dusty sky toward the constellation Taurus and the Orion Arm of our Milky Way Galaxy, this remarkable image shows the famous star cluster at the upper left. But lesser known dusty nebulae lie along the region's fertile molecular cloud, within the 10 degree wide field, including the bird-like visage of LBN 777 near center. Small bluish reflection nebula VdB 27 at the lower right is associated with the young, variable star RY Tau. At the distance of the Pleiades, the 5 panel mosaic spans nearly 70 light-years.

APOD: 2010 November 17 - Frosted Leaf Orion
Explanation: Sometimes, you can put some night sky in your art. Captured above Japan earlier this month, a picturesque night sky was photographed behind a picturesque frosted leaf. The reflecting ice crystals on the leaf coolly mimic the shining stars far in the background. The particular background sky on this 48-second wide angle exposure, however, might appear quite interesting and familiar. On the far left, although hard to find, appears a streaking meteor. Below and to the right of the meteor appears a longer and brighter streak of an airplane. The bright star on the left is the dog-star Sirius, the brightest star on the night sky. To Sirius' right appears the constellation of Orion, including the three linear belt stars below the red giant Betelgeuse. The bright patch of light further to the right is the Pleiades open star cluster. Similar views including the constellation Orion can be seen above much of the northern hemisphere for the next several months, although you might have to provide your own leaf.

APOD: 2010 November 1 - The Milky Way Over the Peak of the Furnace
Explanation: On Reunion Island, it is known simply as "The Volcano." To others, it is known as the Piton de la Fournaise, which is French for the Peak of the Furnace. It is one of the most active volcanoes in the world. The Volcano started a new eruption last month by spewing hot lava bombs as high as 10 meters into the air from several vents. Pictured above, the recent eruption was caught before a star filled southern sky, appearing somehow contained beneath the arching band of our Milky Way Galaxy. Also visible in the background sky is the Pleiades open star cluster, the constellation of Orion, the brightest star Sirius, and the neighboring Large and Small Magellanic Cloud galaxies. (Can you find them?) The Piton de la Fournaise erupted for months in 2006, and for days in 2007, 2008, and in January of 2010. Nobody knows how long the current eruption will last, or when The Volcano will erupt next.

APOD: 2010 September 17 - Northern Lights over Prelude Lake
Explanation: Curtains of shimmering green light sprawl across this gorgeous night skyscape. In the foreground lies the peaceful Prelude Lake, located about 30 kilometers east of Yellowknife, Northwest Territories, Canada. From high northern latitudes these mesmerizing northern lights, also known as the aurora borealis, are becoming a more familiar sight. As the September 23rd equinox approaches, nights grow longer and a favorable season for aurora begins. Recorded on September 11, this panoramic scene spans about 180 degrees. Brighter stars peering through the auroral glow at the left form the recognizable northern asterism, the Big Dipper. A more compact Pleiades star cluster shines at the far right.

APOD: 2010 August 21 - Perseid Storm
Explanation: Storms on the distant horizon and comet dust raining through the heavens above are combined in this alluring nightscape. The scene was recorded in the early hours of August 13 from the Keota Star Party site on the Pawnee National Grasslands of northeastern Colorado, USA. Looking east across the prairie, the composite of 8 consecutive exposures each 30 seconds long captures the flash of lightning and a bright Perseid meteor. On the right, even the clouds can't block the light from brilliant planet Jupiter, whose mythological namesake knew how to handle both lightning bolts and meteors. Of course, this meteor's streak points back toward the shower's radiant in the heroic constellation Perseus, sharing a starry background that includes the Pleiades star cluster poised above the storm clouds. Just above the bright meteor lies the faint Andromeda Galaxy.

APOD: 2010 March 29 - Moonset Over Pleasant Bay
Explanation: It was a sky for the imagination. In the early evening last week, the sky illuminating the unaided eye was perhaps even more illuminating to the mind's eye. The unaided eye saw clouds framing the Moon setting over a calm and reflective bay, spruce trees lining the nearby shores, the Pleiades open star cluster (M45) glowing prominently in the center of the sky, the Andromeda galaxy hovering just over the horizon on the right, and the belt stars of Orion lined up on the left, just below the bright orange star Betelgeuse. The bright star Sirius peeked out of the trees on the far left. The mind's eye might further imagine, however, some of the constellations coming to life, with Orion the Hunter taking up his sword and shield, followed into battle by his Big Dog (Canis Major, whose right eye is Sirius), and watched from across the sky by Cassiopeia, the Queen of Ethiopia, sitting on her Throne. The above image was taken over Pleasant Bay, Maine, USA, and digitally merged with constellations from Uranographicarum, drawn in the 17th century by J. Hevelius.

APOD: 2010 March 26 - Young Moon and Sister Stars
Explanation: A young crescent Moon shares the western sky with sister stars of the Pleiades cluster in this pretty, evening skyscape recorded on the March equinox from San Antonio, Texas. In the processed digital image, multiple exposures of the celestial scene were combined to show details of the bright lunar surface along with the Pleiades stars. Astronomical images of the well-known Pleiades often show the cluster's alluring blue reflection nebulae, but they are washed-out here in the bright moonlight. Still, during this particular night, skygazers in South and Central America could even watch the 5 day old Moon occult or pass in front of some of the brighter Pleiades stars.

APOD: 2010 March 20 - Zodiacal Light Vs. Milky Way
Explanation: Ghostly Zodiacal light, featured near the center of this remarkable panorama, is produced as sunlight is scattered by dust in the Solar System's ecliptic plane. In the weeks surrounding the March equinox (today at 1732 UT) Zodiacal light is more prominent after sunset in the northern hemisphere, and before sunrise in the south, when the ecliptic makes a steep angle with the horizon. In the picture, the narrow triangle of Zodiacal light extends above the western horizon and seems to end at the lovely Pleiades star cluster. Arcing above the Pleiades are stars and nebulae along the plane of our Milky Way Galaxy. Recorded on March 10 from Teide National Park on the island of Tenerife, the vista is composed of 4 separate pictures spanning over 180 degrees.

APOD: 2009 December 5 - Himalayan Skyscape
Explanation: Capella, alpha star of the constellation Auriga, rises over Mt. Everest in this panoramic view of the top of the world at night. The scene was recorded in late November near Namche Bazar, Nepal, gateway to the Himalayan mountain range. Moonlight illuminates the famous peaks of Everest (8840 meters) and Lhotse (8516 meters) at the far left, and a stupa (a Buddhist religious monument) in the foreground, along the main trail to the Everest Base Camp. The light in the valley is from the Tengboche Monastery, also along the trail at about 4000 meters. From left to right above the moonlit peaks, the stars of Auriga give way to bright giant star Aldebaran eye of the Taurus the Bull, the Pleiades star cluster, alpha Ceti, and finally alpha Phoenicis of the Phoenix. Peaks and stars can be identified by placing your cursor over the image.

APOD: 2009 November 3 - Seven Sisters Versus California
Explanation: On the upper right, dressed in blue, is the Pleiades. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3,000 stars, is about 400 light years away, and only 13 light years across. Surrounding the stars is a spectacular blue reflection nebula made of fine dust. A common legend is that one of the brighter stars faded since the cluster was named. On the lower left, shining in red, is the California Nebula. Named for its shape, the California Nebula is much dimmer and hence harder to see than the Pleiades. Also known as NGC 1499, this mass of red glowing hydrogen gas is about 1,500 light years away. Although about 25 full moons could fit between them, the above wide angle, deep field image composite has captured them both.

APOD: 2009 October 14 - Pleiades and Stardust
Explanation: Have you ever seen the Pleiades star cluster? Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. Hurtling through a cosmic dust cloud a mere 400 light-years away, the Pleiades or Seven Sisters star cluster is well-known for its striking blue reflection nebulae. This remarkable wide-field (3 degree) image of the region shows the famous star cluster near the center, while highlighting lesser known dusty reflection nebulas nearby, across an area that would span over 20 light-years. In this case, the sister stars and cosmic dust clouds are not related, they just happen to be passing through the same region of space.

APOD: 2009 September 22 - Aurora Over Yellowknife
Explanation: Sometimes, after your eyes adapt to the dark, a spectacular sky appears. In this case, a picturesque lake lies in front of you, beautiful green auroras flap high above you, brilliant stars shine far in the distance, and a brilliant moon shines just ahead of you. This digitally fused panorama was captured earlier this month from Yellowknife, Northwest Territories, Canada, and includes the Pleiades open cluster of stars just to the upper right of the Moon. Since auroras are ultimately started by solar activity, this current flurry of auroras is somewhat surprising, given the historic lack of sunspots and other activity on the Sun over the past two years. This time of year is known as aurora season, however, for noted average increases in auroras. The reason for the yearly increase is not known for sure, but possibly relates to the tilt of the Earth creating a more easily traversable connection between the Earth's magnetic field and the magnetic field of the Sun's changing wind streams.

APOD: 2009 April 30 - Framed by Clouds
Explanation: Last Sunday's fading evening twilight featured a young crescent Moon along the western horizon. The young Moon also shared the sky with the lovely Pleiades star cluster and wandering planet Mercury. Framed by clouds in this serene skyscape from Selsey, UK, a similar twilight scene was visible around the globe. Emerging from the cloud bank below the Pleiades, the narrow sunlit lunar crescent is overexposed. Still, the Moon's dim night side is impressively clear, illuminated by earthshine. Bright, innermost planet Mercury lies near the bottom of the field. Mercury will remain near the Pleiades, low in the west after sunset over the coming days, an ongoing conjunction of planet and star cluster that will offer skygazers some excellent binocular views.

APOD: 2009 April 22 - Sky Panorama Over Lake Salda
Explanation: As midnight approached, a spectacular sky appeared. Such was the case last month from the shore of Lake Salda in southwestern Turkey. In the above night sky panorama, rocky sand covers the foreground, while building lights are visible across the lake. Looking up, the stars of Orion lie just ahead, while Sirius, the brightest star in the sky, appears to Orion's left. To Orion's right, just above the horizon, lies the Pleiades open star cluster. Arching across the sky is the central band of our Milky Way Galaxy. High in the center, the stars Castor and Pollux are visible. Lake Salda is famous partly for its blue color that is slightly discernable even in the above image.

APOD: 2009 April 11 - The Big Picture
Explanation: Intricate, glowing nebulae that shine in planet Earth's night sky are beautiful to look at in deep images made with telescopes and sensitive cameras. But they are faint and otherwise invisible to the naked-eye. That makes their relative location and extent on the sky difficult to appreciate. So, consider this impressive composite image of a wide region of the northern winter sky. With a total exposure time of 40 hours, the painstaking mosaic presents a nebula-rich expanse known as the Orion-Eridanus Superbubble above a house in suburban Boston, USA. Within the wide and deep view are nebulae more often seen in narrower views, including the Great Orion Nebula, the Rosette Nebula, the Seagull Nebula, the California Nebula, and Barnard's Loop. The familiar constellation of Orion itself is just above the foreground house. Brightest star Sirius is left of the roof, and the recognizable Pleiades star cluster is above the tree at the right. A version of the big picture that includes simple constellation guidelines is available here.

APOD: 2009 February 12 - Zodiacal Light Vs. Milky Way
Explanation: Two fundamental planes of planet Earth's sky compete for attention in this remarkable wide-angle vista, recorded on January 23rd. Arcing above the horizon and into the night at the left is a beautiful band of Zodiacal Light - sunlight scattered by dust in the solar system's ecliptic plane. Its opponent on the right is composed of the faint stars, dust clouds, and nebulae along the plane of our Milky Way Galaxy. Both celestial bands stand above the domes and towers of the Teide Observatory on the island of Tenerife. Also out to play in the pristine, dark skies over the Canary Islands, are brilliant Venus (lower left), the distant Andromeda Galaxy (near center), and the lovely Pleiades star cluster (top center). Of course, seasoned skygazers might even spot M33, the California Nebula, IC1805, and the double star cluster of Perseus. (Need some help? Just slide your cursor over the picture.)

APOD: 2008 December 9 - M45: The Pleiades Star Cluster
Explanation: Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3,000 stars, is about 400 light years away, and only 13 light years across. A prominent telescope and car company has borrowed the star cluster's name. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades.

APOD: 2008 July 3 - Hoodoo Sky
Explanation: The strange-looking rock formations in the foreground of this skyscape are called hoodoos. Towers of weathered, eroded sedimentary rock, hoodoos are found in arid regions of planet Earth and are particularly abundant in an area known as Bryce Canyon National Park in southern Utah, USA. The more familiar night sky pictured here was recorded early Monday morning and includes bright star Capella, alpha star of the constellation Auriga, left of center. On the far right, a very over exposed crescent Moon dominates the sky in close conjunction with the sister stars of the Pleiades cluster. The curious shapes of the two tall, illuminated hoodoos suggest their popular monikers; Thor's Hammer (right) and The Temple of Osiris.

APOD: 2008 July 2 - Night Shinings
Explanation: In the early morning hours of June 30th, ghostly clouds hovered in the east in this view of near dawn skies over western France. The noctilucent or night-shining clouds lie near the edge of space, reflecting sunlight from about 80 kilometers above Earth's surface. Usually spotted above the poles in summer, they are now seen with increasing frequency farther from the poles, in this case extending to the photographer's latitude of about 48 degrees north. The trend could be a telltale sign of global changes in the atmosphere. Another 400,000 kilometers away, the Moon's sunlit crescent shines brightly, its night side illuminated by Earthshine. Of course, as a bonus for early risers June's old crescent Moon was followed closely across the sky by the lovely Pleiades star cluster, surrounded by cosmic dust clouds and shining from a mere 400 light-years away.

APOD: 2008 May 7 - The Gegenschein Over Chile
Explanation: Is the night sky darkest in the direction opposite the Sun? No. In fact, a rarely discernable faint glow known as the gegenschein (German for "counter glow") can be seen 180 degrees around from the Sun in an extremely dark sky. The gegenschein is sunlight back-scattered off small interplanetary dust particles. These dust particles are millimeter sized splinters from asteroids and orbit in the ecliptic plane of the planets. Pictured above from last October is one of the most spectacular pictures of the gegenschein yet taken. Here a deep exposure of an extremely dark sky over Paranal Observatory in Chile shows the gegenschein so clearly that even a surrounding glow is visible. In the foreground are several of the European Southern Observatory's Very Large Telescopes, while notable background objects include the Andromeda galaxy toward the lower left and the Pleiades star cluster just above the horizon. The gegenschein is distinguished from zodiacal light near the Sun by the high angle of reflection. During the day, a phenomenon similar to the gegenschein called the glory can be seen in reflecting air or clouds opposite the Sun from an airplane.

APOD: 2008 January 19 - Starry Night Castle
Explanation: The tantalizing Pleiades star cluster seems to lie just beyond the trees above a dark castle tower in this dramatic view of The World at Night. Recorded earlier this month, the starry sky also features bright star Aldebaran below the Pleiades and a small, faint, fuzzy cloud otherwise known as Comet Holmes near picture center at the top of the field. Starry Night Castle might be an appropriate name for the medieval castle ruin in the foreground. But its traditional name is Mörby Castle, found north of Stockholm, near lake Skedviken in Norrtälje, Sweden.

APOD: 2007 December 21 - Horizon to Horizon
Explanation: Scroll right and journey from horizon to horizon as your gaze sweeps through the zenith in the night sky over Beg-Meil, France. Recorded on December 13th, the entertaining panorama (image key) covers 210 degrees in 21 separate exposures, beginning on the beach with bright star Sirius rising in the southeast. Look up (pan right) to encounter the nebula rich constellation of Orion and continue on to find the lovely Pleiades star cluster. Farther along, higher in the sky, is the famous Comet Holmes, still gracing the northern hemisphere's night with its remarkable expanding coma. Finally, just before diving into the urban glow from city lights along the northwestern horizon (far right), check out the double star cluster in Perseus and take in the cosmic streak of a bright Geminid Meteor.

APOD: 2007 November 22 - Pleiades and Stardust
Explanation: Hurtling through a cosmic dust cloud a mere 400 light-years away, the lovely Pleiades or Seven Sisters star cluster is well-known for its striking blue reflection nebulae. This remarkable wide-field (3 degree) image of the region shows the famous star cluster at the right, while highlighting lesser known dusty reflection nebulae nearby, across an area that would span over 20 light-years. In this case, the sister stars and cosmic dust clouds are not related, they just happen to be passing through the same region of space. But astronomers using infrared detectors have recently found a dusty disk that really does belong to one young Pleiades star -- HD 23514. Surrounding HD 23514, the disk is estimated to be comparable in size to the terrestrial planet zone in our own solar system and likely represents the debris from the process of rocky planet formation.

APOD: 2007 November 18 - M45: The Pleiades Star Cluster
Explanation: Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades.

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 October 9 - Aurora, Stars, Meteor, Lake, Alaska
Explanation: Sometimes, after your eyes adapt to the dark, a spectacular sky appears. In this case, a picturesque lake lies in front of you, beautiful green aurora flap high above you, brilliant stars shine far in the distance, and, for a brief moment, a bright meteor streaks by. This digitally fused breathtaking panorama was captured late last month across one of the Chena Lakes in North Pole, Alaska, USA, and includes the Pleiades open cluster of stars on the image right. The shot is unusual not only for the many wonders it has captured simultaneously, but because lakes this far north tend to freeze and become non-reflecting before a sky this dark can be photographed.

APOD: 2007 August 16 - Moonless Perseid Sky
Explanation: Last weekend, dark, moonless night skies brought many sightings of Perseid meteors to skygazers all over planet Earth. Early Sunday morning astronomer John Chumack's camera captured this Perseid meteor streak with a flare near the end of its track over Yellow Springs, Ohio. The single, four minute long exposure looks toward the constellation of Taurus and the eastern horizon. The meteor streak points back to the annual meteor shower's radiant in Perseus off the upper left corner of the picture. Of course, the view includes the well-known Pleiades Star cluster (near top center) with a bright yellowish planet Mars below it. Also seen with a yellowish tint but not quite as bright as Mars, the giant star Aldebaran anchors the V-shaped Hyades star cluster left of center, above the trees.

APOD: 2007 August 15 - Mysterious Streaks Over Turkey
Explanation: What are they? Five streaks near the bottom of the above image taken near Ankara, Turkey on Sunday would be identified at first glance as meteors from the Perseids meteor shower peaking just that night. Unexpectedly, however, these streaks do not point back to the Perseids radiant in Perseus. Their origin is therefore somewhat unclear. The above image was captured over the time span of 40 minutes. Other visible celestial icons include the constellation Orion and the Pleiades star cluster. One hypothesis is that the streaks are part of a microburst from a much less active meteor shower known as the Alpha Ursae Majorids. Another possibility is that they are parts of a satellite that broke up as it re-entered the Earth's atmosphere. A discussion of these possibilities can be found here. This year's Perseids meteor shower was a good one, as it was particularly active and corresponded with the dark skies that come with a new moon.

APOD: 2007 June 11 - The Merope Reflection Nebula
Explanation: Reflection nebulas reflect light from a nearby star. Many small carbon grains in the nebula reflect the light. The blue color typical of reflection nebula is caused by blue light being more efficiently scattered by the carbon dust than red light. The brightness of the nebula is determined by the size and density of the reflecting grains, and by the color and brightness of the neighboring star(s). NGC 1435, pictured above, surrounds Merope (23 Tau), one of the brightest stars in the Pleiades (M45). The Pleiades nebulosity is caused by a chance encounter between an open cluster of stars and a molecular cloud.

APOD: 2007 April 28 - Young Moon and Sister Stars
Explanation: A young crescent Moon shared the western sky with thin clouds and the sister stars of the Pleiades cluster in this early evening skyscape recorded on April 19th. Astronomical images of the well-known Pleiades often show the star cluster's alluring blue reflection nebulae, but they are washed-out here in the clouds and bright moonlight. While the 3-day old Moon is overexposed, surface features can be seen on the dim lunar night side, illuminated by earthshine - light from sunlit planet Earth. Only a week earlier, brilliant Venus also posed near the sister stars. Of course, Venus has not yet wandered too far from the Pleiades and still rules western skies as the evening star.

APOD: 2007 April 14 - Venus by the Lake
Explanation: Finding Venus in the night sky is not too hard these days. Now appearing as the evening star, Venus rules as the brightest celestial beacon in west just after sunset. And if you can find Venus tonight, you can also easily find the lovely Pleiades star cluster (aka M45) close by. In this serene skyview, recorded on Tuesday near Bolu, Turkey, Venus and the Pleiades are on the right, with brilliant Venus reflected in the calm waters of the small lake in the foreground. Left of Venus, the bright star Aldebaran anchors the V-shaped Hyades star cluster. Farther left are stars of the familiar constellation Orion with Rigel, at the foot of Orion, also reflected in the lake. Meanwhile, Sirius, in Canis Major, is the brightest star on the left side of the view. But the bright terrestrial light below Sirius is not a reflection, it's just a light near the lake shore.

APOD: 2007 April 13 - Seven Dusty Sisters
Explanation: Hurtling through a cosmic dust cloud a mere 400 light-years away, the lovely Pleiades or Seven Sisters star cluster is well-known in astronomical images for its striking blue reflection nebulae. At visible wavelengths, the starlight is scattered and reflected by the dust, but in this portrait in infrared light by the Spitzer Space Telescope, the dust itself glows. The false color image spans about 1 degree or seven light-years at the distance of the Pleiades, with the densest regions of the dust cloud shown in yellow and red hues. Exploring this young, nearby cluster, the Spitzer data have revealed many cool, low mass stars, brown dwarfs or failed stars, and possible planetary debris disks. Want to see the Pleiades tonight? Look near Venus, the brilliant evening star in the west just after sunset.

APOD: 2006 July 20 - Constellation Construction
Explanation: This lovely twilight scene, recorded last April, finds a young crescent Moon low in the west at sunset. Above it, stars shine in the darkening sky but they too are soon to drop below the western horizon. These stars and constellations are prominent in the northern hemisphere winter sky and as the season changes, slowly give way to the stars of summer. Sliding your mouse over the picture will detail the constellations and stars in view, including Orion, Gemini, Auriga, Perseus, and the Hyades and Pleiades star clusters.

APOD: 2006 July 15 - Reflecting Merope
Explanation: In the well known Pleiades star cluster, starlight is slowly destroying this wandering cloud of gas and dust. The star Merope lies just off the upper left edge of this picture from the Hubble Space Telescope. In the past 100,000 years, part of the cloud has by chance moved so close to this star - only 3,500 times the Earth-Sun distance - that the starlight itself is having a very dramatic effect. Pressure of the star's light significantly repels the dust in the reflection nebula, and smaller dust particles are repelled more strongly. As a result, parts of the dust cloud have become stratified, pointing toward Merope. The closest particles are the most massive and the least affected by the radiation pressure. A longer-term result will be the general destruction of the dust by the energetic starlight.

APOD: 2006 June 29 - Old Moon and Sister Stars
Explanation: An old crescent Moon shares the eastern sky over Menton, France with the sister stars of the Pleiades cluster in this early morning skyscape recorded just last Friday, June 23rd. (Bright Venus was also near the eastern horizon, but is not pictured here.) Astronomical images of the well-known Pleiades often show the cluster's alluring blue reflection nebulae, but they are washed out here by the bright moonlight. Still, while the crescent Moon is overexposed, surface features can be seen on the dim lunar night side illuminated by earthshine - light from sunlit planet Earth. Of course, you can spot a young crescent Moon in the early evening sky tonight. Having left the Pleiades behind, a lovely lunar crescent now appears in the west, lining up with planets Mars, Saturn, and Mercury along the solar system's ecliptic plane.

APOD: 2006 April 22 - Z is for Mars
Explanation: This composite of images spaced about a week apart - from late July 2005 (bottom right) through February 2006 (top left) - traces the retrograde motion of ruddy-colored Mars through planet Earth's night sky. On November 7th, 2005 the Red Planet was opposite the Sun in Earth's sky (at opposition). That date occurred at the center of this series with Mars near its closest and brightest. But Mars didn't actually reverse the direction of its orbit to trace out the Z-shape. Instead, the apparent backwards or retrograde motion with respect to the background stars is a reflection of the motion of the Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, the Earth moving more rapidly through its own relatively close-in orbit. The familiar Pleiades star cluster lies at the upper left.

APOD: 2006 January 9 - M45: The Pleiades Star Cluster
Explanation: Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades. (Editors' note: The prominent diffraction spikes are caused by the telescope itself and may be either distracting or provide aesthetic enhancement, depending on your point of view.)

APOD: 2005 September 16 - Northern Lights, September Skies
Explanation: So far, the Aurora Borealis or Northern Lights have made some remarkable visits to September's skies. The reason, of course, is the not-so-quiet Sun. In particular, a large solar active region now crossing the Sun's disk has produced multiple, intense flares and a large coronal mass ejection (CME) that triggered wide spread auroral activity just last weekend. This colorful example of spectacular curtains of aurora was captured with a fish-eye lens in skies over Quebec, Canada on September 11. Also featured is the planet Mars, the brightest object above and left of center. Seen near Mars (just below and to the right) is the tightly knit Pleiades star cluster. Although they can appear to be quite close, the northern lights actually originate at extreme altitudes, 100 kilometers or so above the Earth's surface.

APOD: 2005 April 14 - April's Moon and the Pleiades
Explanation: After parting with the Sun late last week, April's moon graced the early evening sky. Its slender, three-day-old crescent shares this lovely telescopic skyview with the nearby Pleiades star cluster. Here, the Moon's sunlit crescent is overexposed while the lunar terminator, or boundary between lunar night and day, is jagged with craters and mountains. Lunar surface features can also be seen in the dim lunar night illuminated by earthshine - light from sunlit planet Earth. The sister stars of the Pleiades are grouped at the right, but their alluring blue reflection nebulae, usually highlighted in telescopic images of the cluster, are washed-out in the much brighter moonlight.

APOD: 2005 January 11 - Machholz Meets the Pleiades
Explanation: Sweeping northward in planet Earth's sky, comet Machholz extended its long ion tail with the Pleiades star cluster in the background on January 7th. This stunning view, recorded with a telephoto lens in skies over Oberjoch, Bavaria, Germany, emphasizes faint, complex tail structures and the scene's lovely blue and green colors. Merging with the blue dust-reflected starlight of the Pleiades, colors in the comet's ion tail and greenish coma are produced as gas molecules fluoresce in sunlight. Reflecting the sunlight, dust from comet Machholz trails along the comet's orbit and forms the whitish tail jutting down and toward the right. While the visible coma spans about 500,000 kilometers, the nucleus of the comet, likely only a few kilometers across, lies hidden within. Comet tails can extend many millions of kilometers from the nucleus, but appear substantially shortened because of perspective.

APOD: 2005 January 5 - Comet Machholz in View
Explanation: Good views of Comet Machholz are in store for northern hemisphere comet watchers in January. Now making its closest approach to planet Earth, the comet will pass near the lovely Pleiades star cluster on January 7th and the double star cluster in Perseus on January 27th as Machholz moves relatively quickly through the evening sky. Currently just visible to the unaided eye from dark locations, the comet should be an easy target in binoculars or a small telescope. In fact, this telephoto time exposure from January 1 shows Comet Machholz sporting two lovely tails in skies over Colorado, USA. Extending to the left, strands of the comet's ion or gas tail are readily affected by the solar breeze and point away from the Sun. Dust, which tends to trail along the comet's orbit, forms the tail jutting down and to the right.

APOD: 2005 January 3 - The Pleiades Star Cluster
Explanation: Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades. (Editors' note: The prominent diffraction spikes are caused by the telescope itself and may be either distracting or provide aesthetic enhancement, depending on your point of view.)

APOD: 2004 December 4 - Reflecting Merope
Explanation: In the well known Pleiades star cluster, a star's light is slowly destroying this wandering cloud of gas and dust. Above, the star Merope lies just off the upper left edge of this picture from the Hubble Space Telescope. The cloud, known as IC 349, and the star have been in existence for millions of years. In the past 100,000 years, however, part of the cloud has by chance moved so close to the star - only 3,500 times the Earth-Sun distance - that the starlight itself is having a very dramatic effect. Pressure of the star's light significantly repels the dust in the reflection nebula with smaller dust particles being repelled more strongly. Eventually parts of the dust cloud have become stratified and point toward Merope, with the closest particles being the most massive and so the least affected by the radiation pressure. A longer-term result will be the general destruction of the dust by the energetic starlight.

APOD: 2004 September 24 - Fornax Cluster in Motion
Explanation: Reminiscent of popular images of the lovely Pleiades star cluster that lies within our own Milky Way Galaxy, this false-color x-ray view actually explores the center of a much more extended cosmic family -- the Fornax cluster of galaxies some 65 million light-years away. Spanning nearly 900,000 light-years, the Chandra Observatory composite image reveals high-energy emission from several giant galaxies near the Fornax cluster center and an immense, diffuse cloud of x-ray emitting hot gas. On the whole, the hot cluster gas seems to be trailing toward the upper left in this view. As a result, astronomers surmise that the Fornax cluster core is moving toward the lower right, encountering an intergalactic headwind as it sweeps through a larger, less dense cloud of material. In fact, along with another visible galaxy grouping at the outskirts of the cluster, the Fornax cluster core galaxies seem to be moving toward a common point, attracted by the dominating gravity of unseen structures of dark matter in the region.

APOD: 2004 August 13 - Perseid Fireball Over Japan
Explanation: Enjoying the bright Moon's absence from early morning skies, observers around the world reported lovely displays during this year's Perseid meteor shower. As anticipated, peak rates were about one meteor per minute. Though most Perseids were faint, this bright and colorful fireball meteor flashed through skies over Japan on August 12 at 0317 JST. Ending at the upper right, the meteor's trail points down and to the left, back to the shower's radiant point between the constellations of Perseus and Cassiopeia, seen here just above the tower structure in the foreground. The Pleiades star cluster is also visible well below the meteor's trail. Perseid shower meteors can be traced to particles of dust from the tail of comet Swift-Tuttle. The comet dust impacts the atmosphere at speeds of around 60 kilometers per second. While this annual shower's peak has come and gone, Perseid meteors should still be visible over the next few nights, but at a greatly reduced rate.

APOD: 2004 April 15 - Venus and the Pleiades
Explanation: Venus still rules the western skies after sunset as the brilliant evening star. While wandering the ecliptic with its fellow naked-eye planets earlier this month, it passed near the Pleiades star cluster, providing a striking photo opportunity for earthbound skygazers. Cataloged as M45, the Pleiades stars make for a lovely sight on their own, often shown in long exposure images immersed in hazy blue reflection nebulae. In this picture though, recorded on the evening of April 3rd, brilliant Venus closes with the Seven Sisters and overwhelms the light from the delicate cosmic clouds. The view offers a study in contrasts as Venus appears about 700 times brighter than Alcyone, the Pleiades brightest star. With Venus just over 5 light-minutes from Earth, Alcyone and the other Pleiades cluster stars are about 400 light-years distant. Formed out of the contracting nebula which gave birth to the Sun, Venus is also roughly 4.5 billion years old. The stars of the Pleiades are likely aged a mere hundred million years.

APOD: 2004 April 2 - Mercury and Venus in the West
Explanation: Doing their part in the ongoing dance of the planets, Mercury and Venus both reached their greatest elongation or maximum apparent distance from the Sun only a few days ago, on March 29th. Eager to record their celestial accomplishment, astronomer Jimmy Westlake snapped this view of the two inner most planets shining in western twilight skies above Yampa, Colorado, USA. The picture was taken using a digital camera mounted on a tripod. Mercury is easily the brightest celestial object near the horizon, appearing to the right of the foreground structure and just above a thin cloud silhouetted by fading sunlight. Still, near the top of the picture brilliant Venus dominates the scene as the magnificent evening star. After climbing in western skies throughout the month of March, Venus lies just below the Pleiades star cluster. Tonight and tomorrow night, skygazers can spot Venus at the southern edge of the Pleiades.

APOD: 2004 March 26 - Moon and Planets Sky
Explanation: Look up into the sky tonight and without a telescope or binoculars you might have a view like this one of Moon, planets and stars. The lovely photo was taken on March 23rd, and captures the crescent Moon on the horizon with Venus above it. Both brilliant celestial bodies are over-exposed. Farther above Venus is the tinted glow of Mars with the Pleiades star cluster just to the red planet's right. The V-shaped arrangement of stars to the left of Mars is the Hydaes star cluster. Bright red giant Aldebaran, not itself a member of the Hyades cluster, marks the top left of the V. During the next week, all five naked-eye planets, Mercury, Venus, Mars, Jupiter, and Saturn, along with the Moon will grace the evening sky together - a lunar and planetary spectacle that can be enjoyed by skygazers around the world. But look just after sunset, low on the western horizon, to see Mercury before it sets. The next similar gathering of the planets will be in 2008.

APOD: 2003 December 27 - The Pleiades Star Cluster
Explanation: Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades. (Editors' note: The prominent diffraction spikes were added to the image for aesthetic reasons, produced by kite string donated by Rob Gendler's kids and placed over the telescope dew shield.)

APOD: 2002 December 1 - The Pleiades Star Cluster
Explanation: It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.

APOD: 2002 April 29 - Dusk of the Planets
Explanation: A great grouping of planets is now visible to the west just after sunset. Over the next two weeks, Mercury, Venus, Earth, Mars, Jupiter, and Saturn -- the innermost six planets of our Solar System -- can be seen in a single knowing glance. The image on the left captured them all in one frame. Connecting the planetary dots delineates the edge-on ecliptic, the plane in which the planets orbit the Sun. The shot was taken on April 23 near Chatsworth, New Jersey, USA, and even includes scattered light from the Sun and the Moon. Besides the planets, the Pleiades and Hyades open clusters of stars are visible.

APOD: 2002 April 18 - Planets in the West
Explanation: Have you seen any bright planets lately? Chances are if you've been outside under clear skies just after sunset, then you have. Now shining in the west as bright "stars" in the night sky, are all five planets of the solar system known to ancient astronomers - Mercury, Venus, Mars, Saturn, and Jupiter. Recorded from Holt, Michigan, USA about 40 minutes after sunset on April 14th, this digital image captures three of them, Venus, Mars, and Saturn, along with a young crescent Moon. Also indicated are the Pleiades star cluster and bright red giant star Aldebaran in Taurus. Mercury, setting, is lost in the trees and glow along the horizon, while Jupiter is off the top of this view. The coming weeks will see photo opportunities galore as all five planets gradually move closer together, posing after sunset with the Moon and stars in the western sky. Venus, Mars, and Saturn will form the closest trio, drawing within a 5 degree circle (about the apparent size of your fist with arm extended) above Aldebaran by May 3rd.

APOD: 2002 January 18 - Saturn and Vesta in Taurus
Explanation: Last November, while skygazing toward the constellation Taurus, astrophotographer Joe Orman arranged this time exposure to include the lovely Hyades and Pleiades star clusters in the field of his telephoto lens. A distance of 400 light-years for the close-knit Pleiades and 150 light-years for the V-shaped Hyades puts these clusters in the general galactic neighborhood of the Sun. Punctuating the Hyades' appearance, bright yellow Aldebaran, 60 light-years away, is not actually a member of the cluster, but it is Taurus' brightest star. Above Aldebaran a yellower, even brighter Saturn is is seen about 1.2 light-hours from our fair planet. Last and least massive, one of the faint specks below Aldebaran is main-belt asteroid Vesta, a mere 13 light-minutes away. Still cruising through Taurus, Vesta is steadily approaching a close alignment or conjunction with Saturn on March 19. Need a program to follow the players? Click on the image for a labeled version.

APOD: 2001 December 28 - Starlight Reflections
Explanation: Interstellar dust grains often find themselves in a reflective "mood". Near a bright star, clouds of these dust particles scatter short wavelengths of visible starlight more readily than long wavelengths, producing lovely blue reflection nebulae. Nine of the more spectacular examples of these dusty, blue stellar neighborhoods have been assembled here by astrophotographer Rob Gendler. From left to right starting with the top row are NGC 1977 in Orion, IC2118 (the Witch Head), and M78 also in Orion. Across the middle row are, M20 (Trifid), NGC 2264 in Monoceros, and IC405 (Flaming Star Nebula). Along the bottom are NGC 2023 (near the Horsehead), NGC 7023 (Iris Nebula), and finally bright star Merope surrounded by a veil of dust (NGC 1435). Merope is one of the seven sisters of the Pleiades.

APOD: 2001 December 20 - Jupiter and Saturn Pas de Deux
Explanation: Viewed from Earth, the solar system's planets do a cosmic dance that is hard to appreciate on any single night. But consider this well planned animated sequence combining 23 pictures taken at approximately 2 week intervals from June 2000 through May 2001. It reveals the graceful looping or retrograde motion of bright wanderers Jupiter (leftmost) and Saturn. Loitering among the background stars are the familiar Pleiades (above right) and V-shaped Hyades (below left) star clusters. The planets didn't actually loop by reversing the direction of their orbits, though. Their apparent retrograde motion is a reflection of the motion of the Earth itself. Retrograde motion can be seen each time Earth overtakes and laps planets orbiting farther from the Sun, Earth moving more rapidly through its own relatively close-in orbit. Astronomer Tunc Tezel captured Jupiter and Saturn's "paired" retrograde loop in this remarkable series made after the close alignment of these gas giants in May 2000. The next opportunity to see these two planets dance such a pas de deux will be in the year 2020.

APOD: 2001 November 20 - A Leonids Star Field
Explanation: As meteor after meteor streaked across a moonless sky, photographers across the world snapped pictures of the 2001 Leonids Meteor Shower. Many recognized this as the best meteor shower they had ever seen. In fact, the 2001 Leonids was the most active meteor shower since the mid-1960s. The above photo captures three Leonid meteors crossing a photogenic star-field. On the far right is the Pleiades star cluster. The brightest meteor crosses right in front of the Hyades star cluster, situated below the image center. Just left of center is the bright planet Saturn, and the bright star below Saturn is Aldebaran. The ten-minute exposure was taken near Victoria, British Columbia, Canada at 2:45 am PST on 2001 November 18.

APOD: 2001 August 7 - A July Dawn
Explanation: Those up before dawn in late July in the northern hemisphere could see planets, stars, and a spacecraft in a single quick glance before starting their day. Near the eastern horizon was bright Jupiter, and not far above and to its right was the very bright Venus. Connecting the dots will point you just right of Saturn. Far in the distance but near the top right of the frame is the Pleiades star cluster. Orbiting the Earth well in the foreground, the International Space Station reflected sunlight to cause the faint line segment. In the very close foreground, the bright red and yellow lines were caused by a passing van. The above picture was taken on July 26 from Quebec, Canada. Why are bushes visible through the van? The van was present for only a few of the 25 seconds of the total exposure.

APOD: 2001 May 6 - The Pleiades Star Cluster
Explanation: It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.

APOD: 2001 March 22 - Jupiter, Saturn and Messier 45
Explanation: Brilliant Venus falls out of the evening sky as March ends, but Jupiter and Saturn remain well up above the western horizon. Jupiter blazes forth above and to the left of a slightly fainter Saturn in this telephoto picture taken on January 19th. Near the top lies the lovely Pleiades star cluster with suggestions of its characteristic blue reflection nebulae. These planets and the Pleiades have a similar, easily recognizable orientation in the Spring night sky. Also known as M45, the 45th object in French astronomer Charles Messier's famous catalog, the Pleiades will likely soon be checked off many stargazers' tally lists. For northern hemisphere observers this weekend offers a prime opportunity to complete a Messier Marathon -- the viewing of all 110 Messier catalog objects in one glorious dusk to dawn observing run. This weekend it will also be possible to complete an all-planet marathon, observing all the solar system's planets in a single night. And if you still need something to look at, the International Space Station could also be visible arcing through the skies depending on your location, but Mir will not.

APOD: 2000 December 6 - Reflecting Merope
Explanation: In the famous Pleiades star cluster, a star's light is slowly destroying a passing cloud of gas and dust. The star, Merope, lies just off the upper right edge of this recently released picture by the Hubble Space Telescope. The cloud, known as IC 349, and the star have been in existence for millions of years. In the past 100,000 years, however, part of the cloud has by chance moved so close to the star - only 3500 times the Earth-Sun distance - that the star's light affects the cloud's dust in an unusual manner. Pressure of the star's light significantly repels the dust in the reflection nebula with smaller dust particles being repelled more strongly. Eventually parts of the dust cloud have become stratified and point toward Merope, with the closest particles being the most massive and so the least affected by the radiation pressure. A longer-term result is the general destruction of the dust by the energetic starlight. It is not known whether the cloud will survive this encounter.

APOD: 2000 November 8 - October Skylights
Explanation: With brilliant Venus above the western horizon at sunset and Jupiter and Saturn high in the east by early evening, November's night sky is filled with bright planets. October's sky featured bright planets as well and, triggered by the active Sun, some lovely auroral displays. This colorful aurora was recorded by astrophotographer Wade Clark in skies above Hamilton, Washington, USA on the night of October 4th. Through the shimmering northern lights Jupiter and Saturn are easy to spot flanking the V-shaped head of Taurus the Bull. Of course, just above lies the lovely Pleiades star cluster. Solar activity will also produce auroral shows in November, particularly at high northern and southern latitudes. Plus, November skygazers can certainly anticipate a celestial performance on the evening of the 17th/18th -- the moonlit Leonid meteor shower.

APOD: 2000 September 29 - September Sky
Explanation: Star clusters, planets, and a red giant posed for this portrait of the night sky from rural Jasper County, Iowa, USA. Astrophotographer Stan Richard recorded the four minute time exposure looking east around midnight on September 3rd at Ashton-Wildwood Park. To avoid star trails, his camera was mounted on a barndoor-style tracker to compensate for the Earth's rotation. Can you identify his celestial subjects? (Click on the image for a labeled version.) The Pleiades and Hyades, the closest open or galactic star clusters to the Sun, should be recognizable to beginning stargazers. Of course gas giant Jupiter rules as the brightest object in the picture and the largest planet in the Solar System, but second largest planet Saturn is also visible nearby. For sheer size cool red giant star Aldebaran is more impressive though, spanning about forty times the diameter of the Sun. Sixty light-years away and yellowish in this picture, Aldebaran is known as Alpha Tauri, the brightest star in Taurus, the Bull.

APOD: 2000 May 24 - Pleiades, Planets, And Hot Plasma
Explanation: Bright stars of the Pleiades, four planets, and erupting solar plasma are all captured in this spectacular image from the space-based SOlar and Heliospheric Observatory (SOHO). In the foreground of the 15 degree wide field of view, a bubble of hot plasma, called a Coronal Mass Ejection (CME), is blasting away from the active Sun whose position and relative size is indicated by the central white circle. Beyond appear four of the five naked-eye planets -- courtesy of the planetary alignment which did not destroy the world! In the background are distant stars and the famous Pleiades star cluster, also easily visible to the unaided eye when it shines in the night sky. Distances for these familiar celestial objects are; the Sun, 150 million kilometers away; Mercury, Venus, Jupiter, and Saturn, about 58, 110, 780, and 1,400 million kilometers beyond the Sun respectively; and the Pleiades star cluster at a mere 3,800 trillion kilometers (400 light-years). SOHO itself orbits 1.5 million kilometers sunward of planet Earth. The image was recorded by the Large Angle and Spectrometric COronagraph (LASCO) instrument on board SOHO on Monday, May 15 at 10:42 UT.

APOD: 2000 May 4 - Planets Above The Clouds
Explanation: Clouds scatter the faint orange rays of the setting sun in the foreground of this breathtaking photograph from the summit of Mauna Kea, Hawaii. Taken on April 7th, this skyscape features a dramatic lunar and planetary alignment. An overexposed crescent moon dominates the celestial scene, but the bright "star" just below and to its right is Saturn while further below Saturn is a close pairing of brilliant Jupiter and a fainter, yellowish Mars. Red giant star Aldebaran is almost directly above the moon near the top of the image and the bright blue stars of the Pleiades cluster are visible about midway up and to the right of the moon-Aldebaran line. The good news is that planetary alignments like this one do not portend disasters, are relatively common, and can clearly make inspirational viewing for casual stargazers and astronomers alike. The bad news is that the world is not going to end because of the highly publicized planetary alignment occurring tomorrow, May 5th -- so you probably will have to go to work!

APOD: 2000 March 2 - NGC 1999: Reflection Nebula In Orion
Explanation: A dusty bright nebula contrasts dramatically with a dusty dark nebula in this Hubble Space Telescope image recorded shortly after December's orbital servicing mission. The nebula, cataloged as NGC 1999, is a reflection nebula, which shines by reflecting light from a nearby star. Unlike emission nebulae, whose reddish glow comes from excited atoms of gas, reflection nebulae have a bluish cast as their interstellar dust grains preferentially reflect blue starlight. While perhaps the most famous reflection nebulae surround the bright young stars of the Pleiades star cluster, NGC 1999's stellar illumination is provided by the embedded variable star V380 Orionis, seen here just left of center. Extending right of center, the ominous dark nebula is actually a condensation of cold molecular gas and dust so thick and dense that it blocks light. From our perspective it lies in front of the bright nebula, silhouetted against the ghostly nebular glow. New stars will likely form within the dark cloud, called a Bok globule, as self-gravity continues to compress its dense gas and dust. Reflection nebula NGC 1999 lies about 1500 light-years away in the constellation Orion, just south of Orion's well known emission nebula, M42.

APOD: 2000 February 27 - The Pleiades Star Cluster
Explanation: It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.

APOD: August 28, 1999 - X-Ray Pleiades
Explanation: The Pleiades star cluster is one of the jewels of the northern sky. To the unaided eye it appears as an alluring group of stars in the constellation Taurus, while telescopic views reveal cluster stars surrounded by delicate blue wisps of dust-reflected starlight. To the X-ray telescopes on board the orbiting ROSAT observatory, the cluster also presents an impressive, but slightly altered, appearance. This false color image was produced from ROSAT observations by translating different X-ray energy bands to visual colors - the lowest energies are shown in red, medium in green, and highest energies in blue. (The green boxes mark the position of the seven brightest visual stars.) The Pleiades stars seen in X-rays have extremely hot, tenuous outer atmospheres called coronas and the range of colors corresponds to different coronal temperatures.

APOD: March 1, 1999 - Reflection Nebula NGC 1435
Explanation: Reflection nebulae reflect light from a nearby star. Many small carbon grains in the nebula reflect the light. The blue color typical of reflection nebula is caused by blue light being more efficiently scattered by the carbon dust than red light. The brightness of the nebula is determined by the size and density of the reflecting grains, and by the color and brightness of the neighboring star(s). NGC 1435, pictured above, surrounds Merope (23 Tau), one of the brightest stars in the Pleiades (M45). The Pleiades nebulosity is caused by a chance encounter between an open cluster of stars and a molecular cloud. The unusual area on the far left, known as Bernard's Merope Nebula (IC 349), reflects visible light with unusually high efficiency.

APOD: October 25, 1998 - The Pleiades Star Cluster
Explanation: It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.

APOD: April 5, 1998 - X-Ray Pleiades
Explanation: The Pleiades star cluster is one of the jewels of the northern sky. To the unaided eye it appears as a lovely and tantalizing grouping of stars in the constellation of Taurus, while telescopic views reveal cluster stars surrounded by delicate blue wisps of dust-reflected starlight. To the X-ray telescopes on board the orbiting ROSAT observatory, the cluster also presents an impressive, but slightly altered, appearance. This false color image was produced from ROSAT observations by translating different X-ray energy bands to visual colors - the lowest energies are shown in red, medium in green, and highest energies in blue. (The green boxes mark the position of the seven brightest visual stars.) The Pleiades stars seen in X-rays have extremely hot, tenuous outer atmospheres called coronas and the range of colors corresponds to different coronal temperatures.

APOD: October 18, 1997 - The Pleiades Star Cluster
Explanation: It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.

APOD: July 23, 1997 - A Hale-Bopp Triple Crown
Explanation: It was truly a busy sky. In one of the more spectacular photos yet submitted to Astronomy Picture of the Day, Don Cooke of Lyme, New Hampshire caught the Sun, Moon, Earth, night sky, Pleiades star cluster, and Comet Hale-Bopp all in one frame. The first leg of this "triple crown" exposure was of the Sun, taken at 6:55 pm on April 10th 1997. Through a dark filter, the Sun appears as the bright dot on the lower right of the image. A second filtered exposure was then taken after the Sun had set, one hour and 40 minutes later - this time featuring the Moon. The Moon appears as a crescent superimposed on an odd-shaped dark circle protruding into the left of the image. This shadow is actually a silhouette of a driveway reflector mounted on an aluminum rod used to block out the bright moon - so as to allow a third exposure, this time unfiltered, of the background night sky. And what a beautiful sky it is. Highlights include Comet Hale-Bopp, on the right, and the Pleiades star cluster, near the center. But what, you may wonder, is that bright light near the center of the picture? Don't worry if you can't guess: it's a porch light from a house across the river!

APOD: May 5, 1997 - Sunset with Hale-Bopp at Keck
Explanation: A famous star cluster and observatory highlight this picture of Comet Hale-Bopp. Taken last week from the observatory summit of Hawaii's Mauna Kea Volcano, the dome of the new 10-meter Keck II telescope appears silhouetted on the lower left. Comet Hale-Bopp is visible on the upper right, and the Pleiades star cluster is visible below the comet. Normally sunset and clouds are to be avoided when making astronomical observations, but Comet Hale-Bopp is not a normal astronomical object. In fact, were it cloudless, Professor Keel would be inside NASA's nearby IRTF dome preparing to observe something else. Comet Hale-Bopp continues to look impressive, although it is fading and moving towards the south.

APOD: March 18, 1997 - X-Ray Pleiades
Explanation: The Pleiades star cluster is one of the jewels of the northern sky. To the unaided eye it appears as a lovely and tantalizing grouping of stars in the constellation of Taurus, while telescopic views reveal cluster stars surrounded by delicate blue wisps of dust-reflected starlight. To the X-ray telescopes onboard the orbiting ROSAT observatory, the cluster also presents an impressive - but slightly altered - appearance. This color image was produced from ROSAT observations by translating different X-ray energy bands to visual colors - the lowest energies are shown in red, medium in green, and highest energies in blue. (The green boxes mark the position of the seven brightest visual stars.) The Pleiades stars seen in X-rays have extremely hot, tenuous outer atmospheres called coronas and the range of colors corresponds to different coronal temperatures.

APOD: September 3, 1996 - The Pleiades Star Cluster
Explanation: It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph is the blue reflection nebula that surrounds the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades.

APOD: June 18, 1996 - Seven Sisters Versus California
Explanation: In the lower left corner, dressed in blue, is the Pleiades. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and most easily visible open clusters on the sky. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Surrounding the stars is a spectacular blue reflection nebula made of fine dust. A common legend is that one of the brighter stars faded since the cluster was named. In the upper right corner, dressed in red, the California Nebula. Named for its shape, the California Nebula is much dimmer and hence harder to see than the Pleiades. Also known as NGC 1499, this mass of red glowing hydrogen gas is about 1500 light years away.

APOD: April 23, 1996 - Comet Hyakutake on a Starry Night
Explanation: It was a starry night in April (April 9th, 1996, 9:32 pm CDT to be exact) near Lone Jack, Missouri when Comet Hyakutake graced this astronomically rich field. Making an appearance as the brilliant evening star, Venus is overexposed at the far left. Just below Venus and slightly to the right, the Pleiades star cluster (M45) glistens. On the right hand side of the image, the comet itself shows a bright blue tail extending upwards past the nearby star cluster in the constellation Perseus (top right, the Alpha Persei Group). Hyakutake, receding from the Earth and appoaching the Sun, will sink into the western horizon at sunset in late April, disappearing from Northern Hemisphere skies.

APOD: June 20, 1995 - Pleiades Star Cluster
Explanation: The Pleiades star cluster, M45, is one of the brightest star clusters visible in the northern hemisphere. It consists of many bright, hot stars that were all formed at the same time within a large cloud of interstellar dust and gas. The blue haze that accompanies them is due to very fine dust which still remains and preferentially reflects the blue light from the stars.