Astronomy Picture of the Day Search Results for "Jupiter"

APOD: 2024 December 5 - Stereo Jupiter near Opposition
Explanation: Jupiter looks sharp in these two rooftop telescope images. Both were captured last year on November 17 from Singapore, planet Earth, about two weeks after Jupiter's 2023 opposition. Climbing high in midnight skies the giant planet was a mere 33.4 light-minutes from Singapore. That's about 4 astronomical units away. Jupiter's planet girdling dark belts and light zones are visible in remarkable detail, along with the giant world's whitish oval vortices. Its signature Great Red Spot is prominent in the south. Jupiter rotates rapidly on its axis once every 10 hours. So, based on video frames taken only 15 minutes apart, these images form a stereo pair. Look at the center of the pair and cross your eyes until the separate images come together to see the 3D effect. Of course Jupiter is now not far from its 2024 opposition. Planet Earth is set to pass between the Solar System's ruling gas giant and the Sun on December 7.

APOD: 2024 November 3 – Jupiter Abyss
Explanation: What's that black spot on Jupiter? No one is sure. During one pass of NASA's Juno over Jupiter, the robotic spacecraft imaged an usually dark cloud feature informally dubbed the Abyss. Surrounding cloud patterns show the Abyss to be at the center of a vortex. Since dark features on Jupiter's atmosphere tend to run deeper than light features, the Abyss may really be the deep hole that it appears -- but without more evidence that remains conjecture. The Abyss is surrounded by a complex of meandering clouds and other swirling storm systems, some of which are topped by light colored, high-altitude clouds. The featured image was captured in 2019 while Juno passed only about 15,000 kilometers above Jupiter's cloud tops. The next close pass of Juno near Jupiter will be in about three weeks.

APOD: 2024 May 19 – Jupiter Diving
Explanation: Take this simulated plunge and dive into the upper atmosphere of Jupiter, the Solar System's ruling gas giant. The awesome animation is based on image data from JunoCam, and the microwave radiometer on board the Jupiter-orbiting Juno spacecraft. Your view will start about 3,000 kilometers above the southern Jovian cloud tops, and you can track your progress on the display at the left. As altitude decreases, temperature increases while you dive deeper at the location of Jupiter's famous Great Red Spot. In fact, Juno data indicates the Great Red Spot, the Solar System's largest storm system, penetrates some 300 kilometers into the giant planet's atmosphere. For comparison, the deepest point for planet Earth's oceans is just under 11 kilometers down. Don't worry though, you'll fly back out again.

APOD: 2024 April 21 – Perijove 16: Passing Jupiter
Explanation: Watch Juno zoom past Jupiter. NASA's robotic spacecraft Juno is continuing on its now month-long, highly-elongated orbits around our Solar System's largest planet. The featured video is from perijove 16, the sixteenth time that Juno passed near Jupiter since it arrived in mid-2016. Each perijove passes near a slightly different part of Jupiter's cloud tops. This color-enhanced video has been digitally composed from 21 JunoCam still images, resulting in a 125-fold time-lapse. The video begins with Jupiter rising as Juno approaches from the north. As Juno reaches its closest view -- from about 3,500 kilometers over Jupiter's cloud tops -- the spacecraft captures the great planet in tremendous detail. Juno passes light zones and dark belts of clouds that circle the planet, as well as numerous swirling circular storms, many of which are larger than hurricanes on Earth. As Juno moves away, the remarkable dolphin-shaped cloud is visible. After the perijove, Jupiter recedes into the distance, now displaying the unusual clouds that appear over Jupiter's south. To get desired science data, Juno swoops so close to Jupiter that its instruments are exposed to very high levels of radiation.

APOD: 2024 January 19 - Jupiter over 2 Hours and 30 Minutes
Explanation: Jupiter, our Solar System's ruling gas giant, is also the fastest spinning planet, rotating once in less than 10 hours. The gas giant doesn't rotate like a solid body though. A day on Jupiter is about 9 hours and 56 minutes long at the poles, decreasing to 9 hours and 50 minutes near the equator. The giant planet's fast rotation creates strong jet streams, separating its clouds into planet girdling bands of dark belts and bright zones. You can easily follow Jupiter's rapid rotation in this sharp sequence of images from the night of January 15, all taken with a camera and small telescope outside of Paris, France. Located just south of the equator, the giant planet's giant storm system, also known as the Great Red Spot, can be seen moving left to right with the planet's rotation. From lower left to upper right, the sequence spans about 2 hours and 30 minutes.

APOD: 2023 December 28 - Jupiter and the Geminid
Explanation: For a brief moment, this brilliant fireball meteor outshone Jupiter in planet Earth's night. The serendipitous image was captured while hunting meteors under cold Canadian skies with a camera in timelapse mode on December 14, near the peak of the Geminid meteor shower. The Geminid meteor shower, asteroid 3200 Phaethon's annual gift, always arrives in December. Dust shed along the orbit of the mysterious asteroid causes the meteor streaks, as the vaporizing grains plow through our fair planet's upper atmosphere at 22 kilometers per second. Of course Geminid shower meteors appear to radiate from a point in the constellation of the Twins. That's below and left of this frame. With bright Jupiter on the right, also in the December night skyview are the Pleiades and Hyades star clusters.

APOD: 2023 November 24 - Stereo Jupiter near Opposition
Explanation: Jupiter looks sharp in these two rooftop telescope images. Both were captured on November 17 from Singapore, planet Earth, about two weeks after Jupiter's 2023 opposition. Climbing high in midnight skies the giant planet was a mere 33.4 light-minutes from Singapore. That's about 4 astronomical units away. Jupiter's planet girdling dark belts and light zones are visible in remarkable detail, along with the giant world's whitish oval vortices. Its signature Great Red Spot is still prominent in the south. Jupiter rotates rapidly on its axis once every 10 hours. So, based on video frames taken only 15 minutes apart, these images form a stereo pair. Look at the center of the pair and cross your eyes until the separate images come together to see the Solar System's ruling gas giant in 3D.

APOD: 2023 November 3 - Jupiter by Moonlight
Explanation: That bright beacon you've seen rising in the east just after sunset is Jupiter. Climbing high in midnight skies, our Solar System's ruling gas giant was at its 2023 opposition, opposite the Sun in planet Earth's sky, on November 2. But only a few days earlier, on October 28, the Moon was at its own opposition. Then both Full Moon and Jupiter could share this telephoto field of view. The celestial scene is composed from two exposures, one long and one short, blended to record bright planet and even brighter Moon during that evening's partial lunar eclipse. Moonlight shining through the thin, high clouds over northern Italy creates the colorful iridescence and lunar corona. Look closely and you'll also spot some of Jupiter's Galilean moons.

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

APOD: 2023 June 25 – Lightning on Jupiter
Explanation: Does lightning occur only on Earth? No. Spacecraft in our Solar System have detected lightning on other planets, including Mars, Jupiter and Saturn, and lightning is likely on Venus, Uranus, and Neptune. Lightning is a sudden rush of electrically charged particles from one location to another. On Earth, drafts of colliding ice and water droplets usually create lightning-generating charge separation, but what happens on Jupiter? Images and data from NASA's Jupiter-orbiting Juno spacecraft bolster previous speculation that Jovian lightning is also created in clouds containing water and ice. In the featured Juno photograph, an optical flash was captured in a large cloud vortex near Jupiter's north pole. During the next few months, Juno will perform several close sweeps over Jupiter's night side, likely allowing the robotic probe to capture more data and images of Jovian lightning.

APOD: 2023 June 13 – Moons Across Jupiter
Explanation: Jupiter's moons circle Jupiter. The featured video depicts Europa and Io, two of Jupiter's largest moons, crossing in front of the grand planet's Great Red Spot, the largest known storm system in our Solar System. The video was composed from images taken by the robotic Cassini spacecraft as it passed Jupiter in 2000, on its way to Saturn. The two moons visible are volcanic Io, in the distance, and icy Europa. In the time-lapse video, Europa appears to overtake Io, which is odd because Io is closer to Jupiter and moves faster. The explanation is that the motion of the fast Cassini spacecraft changes the camera location significantly during imaging. Jupiter is currently being visited by NASA's robotic Juno spacecraft, while ESA's Jupiter Icy Moons Explorer (JUICE), launched in April, is enroute.

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

APOD: 2023 May 23 – Jupiter's Swirls from Juno
Explanation: Big storms are different on Jupiter. On Earth, huge hurricanes and colossal cyclones are centered on regions of low pressure, but on Jupiter, it is the high-pressure, anti-cyclone storms that are the largest. On Earth, large storms can last weeks, but on Jupiter they can last years. On Earth, large storms can be as large as a country, but on Jupiter, large storms can be as large as planet Earth. Both types of storms are known to exhibit lightning. The featured image of Jupiter's clouds was composed from images and data captured by the robotic Juno spacecraft as it swooped close to the massive planet in August 2020.  A swirling white oval is visible nearby, while numerous smaller cloud swirls extend into the distance.  On Jupiter, light-colored clouds are usually higher up than dark clouds. Despite their differences, studying storm clouds on distant Jupiter provides insights into storms and other weather patterns on familiar Earth. 

APOD: 2023 March 15 – Jupiter and Venus Converge over Germany
Explanation: This was a sky to show the kids. Early this month the two brightest planets in the night sky, Jupiter and Venus, appeared to converge. At their closest, the two planets were separated by only about the angular width of the full moon. The spectacle occurred just after sunset and was seen and photographed all across planet Earth. The displayed image was taken near to the time of closest approach from Wiltingen, Germany, and features the astrophotographer, spouse, and their two children. Of course, Venus remains much closer to both the Sun and the Earth than Jupiter -- the apparent closeness between the planets in the sky of Earth was only angular. Jupiter and Venus have passed and now appear increasingly far apart. Similar planetary convergence opportunities will eventually arise. In a few months, for example, Mars and Venus will appear to congregate just as the Sun sets.

APOD: 2023 March 6 – Jupiter and Venus from Earth
Explanation: It was visible around the world. The sunset conjunction of Jupiter and Venus in 2012 was visible almost no matter where you lived on Earth. Anyone on the planet with a clear western horizon at sunset could see them. Pictured here in 2012, a creative photographer traveled away from the town lights of Szubin, Poland to image a near closest approach of the two planets. The bright planets were then separated only by three degrees and his daughter struck a humorous pose. A faint red sunset still glowed in the background. Jupiter and Venus are together again this month after sunset, passing within a degree of each other about a week ago.

APOD: 2023 March 5 – Jupiter and Venus over Italy
Explanation: What are those two bright spots? Planets. A few days ago, the two brightest planets in the night sky passed within a single degree of each other in what is termed a conjunction. Visible just after sunset in much of the world, the two bright spots were Jupiter (left) and Venus (right). The featured image was taken near closest approach from Cirica, Sicily, Italy. The week before, Venus was rising higher in the sunset sky to meet the dropping Jupiter. Now they have switched places. Of course, Venus remains much closer to both the Sun and the Earth than Jupiter -- the apparent closeness between the planets in the sky of Earth was only angular. You can still see the popular pair for an hour or so after sunset this month although they continue to separate, and Jupiter continues to set earlier each night.

APOD: 2023 March 4 - 10 Days of Venus and Jupiter
Explanation: Venus and Jupiter may have caught your attention lately. The impending close conjunction of the two brightest planets visible in clear evening skies has been hard to miss. With Jupiter at the top, starting on February 21 and ending on March 2, their close approach is chronicled daily, left to right, in these panels from Dhanbad, India. Near the western horizon, the evening sky colors and exposures used for each panel depend on the local conditions near sunset. On February 22, Jupiter and Venus were joined by the young crescent Moon. The celestial pair appeared to be only the width of a full moon apart by March 2. Of course on that date the two planets were physically separated by over 600 million kilometers in their orbits around the Sun. In the coming days Jupiter will slowly settle into the glare at sunset, but Venus will continue to move farther from the Sun in the western sky to excel in its current role as the brilliant evening star.

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: 2022 October 25 - Jupiter Rotates as Moons Orbit
Explanation: Jupiter and its moons move like our Sun and its planets. Similarly, Jupiter spins while its moons circle around. Jupiter’s rotation can be observed by tracking circulating dark belts and light zones. The Great Red Spot, the largest storm known, rotates to become visible after about 15 seconds in the 48-second time lapse video. The video is a compilation of shorts taken over several nights last month and combined into a digital recreation of how 24-continuous hours would appear. Jupiter's brightest moons always orbit in the plane of the planet's rotation, even as Earth’s spin makes the whole system appear to tilt. The moons Europa, Ganymede, and Io are all visible, with Europa's shadow appearing as the icy Galilean moon crosses Jupiter's disk. Jupiter remains near opposition this month, meaning that it is unusually bright, near to its closest to the Earth, and visible nearly all night long.

APOD: 2022 October 3 - Jupiter's Europa from Spacecraft Juno
Explanation: What mysteries might be solved by peering into this crystal ball? In this case, the ball is actually a moon of Jupiter, the crystals are ice, and the moon is not only dirty but cracked beyond repair. Nevertheless, speculation is rampant that oceans exist under Europa's fractured ice-plains that could support life. Europa, roughly the size of Earth's Moon, is pictured here in an image taken a few days ago when the Jupiter-orbiting robotic spacecraft Juno passed within 325 kilometers of its streaked and shifting surface. Underground oceans are thought likely because Europa undergoes global flexing due to its changing gravitational attraction with Jupiter during its slightly elliptical orbit, and this flexing heats the interior. Studying Juno's close-up images may further humanity's understanding not only of Europa and the early Solar System but also of the possibility that life exists elsewhere in the universe.

APOD: 2022 August 30 - Jupiter from the Webb Space Telescope
Explanation: This new view of Jupiter is illuminating. High-resolution infrared images of Jupiter from the new James Webb Space Telescope (Webb) reveal, for example, previously unknown differences between high-floating bright clouds -- including the Great Red Spot -- and low-lying dark clouds. Also clearly visible in the featured Webb image are Jupiter's dust ring, bright auroras at the poles, and Jupiter's moons Amalthea and Adrastea. Large volcanic moon Io's magnetic funneling of charged particles onto Jupiter is also visible in the southern aurora. Some objects are so bright that light noticeably diffracts around Webb's optics creating streaks. Webb, which orbits the Sun near the Earth, has a mirror over six meters across making it the largest astronomical telescope ever launched -- with over six times more light-collecting area than Hubble.

APOD: 2022 August 28 - Perijove 11: Passing Jupiter
Explanation: Here comes Jupiter! NASA's robotic spacecraft Juno is continuing on its highly-elongated orbits around our Solar System's largest planet. The featured video is from perijove 11 in early 2018, the eleventh time Juno has passed near Jupiter since it arrived in mid-2016. This time-lapse, color-enhanced movie covers about four hours and morphs between 36 JunoCam images. The video begins with Jupiter rising as Juno approaches from the north. As Juno reaches its closest view -- from about 3,500 kilometers over Jupiter's cloud tops -- the spacecraft captures the great planet in tremendous detail. Juno passes light zones and dark belt of clouds that circle the planet, as well as numerous swirling circular storms, many of which are larger than hurricanes on Earth. After the perijove, Jupiter recedes into the distance, then displaying the unusual clouds that appear over Jupiter's south. To get desired science data, Juno swoops so close to Jupiter that its instruments are exposed to very high levels of radiation.

APOD: 2022 July 20 - Jupiter and Ring in Infrared from Webb
Explanation: Why does Jupiter have rings? Jupiter's main ring was discovered in 1979 by NASA's passing Voyager 1 spacecraft, but its origin was then a mystery. Data from NASA's Galileo spacecraft that orbited Jupiter from 1995 to 2003, however, confirmed the hypothesis that this ring was created by meteoroid impacts on small nearby moons. As a small meteoroid strikes tiny Metis, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit. The featured image of Jupiter in infrared light by the James Webb Space Telescope shows not only Jupiter and its clouds, but this ring as well. Also visible is Jupiter's Great Red Spot (GRS) -- in comparatively light color on the right, Jupiter's large moon Europa -- in the center of diffraction spikes on the left, and Europa's shadow -- next to the GRS. Several features in the image are not yet well understood, including the seemingly separated cloud layer on Jupiter's right limb.

APOD: 2022 July 17 - Europa and Jupiter from Voyager 1
Explanation: What are those spots on Jupiter? Largest and furthest, just right of center, is the Great Red Spot -- a huge storm system that has been raging on Jupiter possibly since Giovanni Cassini's likely notation of it 357 years ago. It is not yet known why this Great Spot is red. The spot toward the lower left is one of Jupiter's largest moons: Europa. Images from Voyager in 1979 bolster the modern hypothesis that Europa has an underground ocean and is therefore a good place to look for extraterrestrial life. But what about the dark spot on the upper right? That is a shadow of another of Jupiter's large moons: Io. Voyager 1 discovered Io to be so volcanic that no impact craters could be found. Sixteen frames from Voyager 1's flyby of Jupiter in 1979 were recently reprocessed and merged to create the featured image. Forty-five years ago this September, Voyager 1 launched from Earth and started one of the greatest explorations of the Solar System ever.

APOD: 2022 April 27 - Moon Shadow on Jupiter
Explanation: What is that large dark spot on Jupiter? It's the shadow of Ganymede, Jupiter's largest moon. When Jupiter's moons cross between the Jovian giant and the Sun, they created shadows just like when the Earth's moon crosses between the Earth and the Sun. Also like on Earth, if you were in a dark shadow on Jupiter, you would see a moon completely eclipse the Sun. Unlike on Earth, moon shadows occur most days on Jupiter -- what's more unusual is that a spacecraft was close enough to record one with a high-resolution image. That spacecraft, Juno, was passing so close to Jupiter in late February that nearby clouds and the dark eclipse shadow appear relatively large. Juno has made many discoveries about our Solar System's largest planet, including, recently, rapidly expanding circular auroras.

APOD: 2022 January 9 - Hubbles Jupiter and the Shrinking Great Red Spot
Explanation: What will become of Jupiter's Great Red Spot? Gas giant Jupiter is the solar system's largest world with about 320 times the mass of planet Earth. Jupiter is home to one of the largest and longest lasting storm systems known, the Great Red Spot (GRS), visible to the left. The GRS is so large it could swallow Earth, although it has been shrinking. Comparison with historical notes indicate that the storm spans only about one third of the exposed surface area it had 150 years ago. NASA's Outer Planets Atmospheres Legacy (OPAL) program has been monitoring the storm more recently using the Hubble Space Telescope. The featured Hubble OPAL image shows Jupiter as it appeared in 2016, processed in a way that makes red hues appear quite vibrant. Modern GRS data indicate that the storm continues to constrict its surface area, but is also becoming slightly taller, vertically. No one knows the future of the GRS, including the possibility that if the shrinking trend continues, the GRS might one day even do what smaller spots on Jupiter have done -- disappear completely.

APOD: 2021 December 29 - Giant Storms and High Clouds on Jupiter
Explanation: What and where are these large ovals? They are rotating storm clouds on Jupiter imaged last month by NASA's Juno spacecraft. In general, higher clouds are lighter in color, and the lightest clouds visible are the relatively small clouds that dot the lower oval. At 50 kilometers across, however, even these light clouds are not small. They are so high up that they cast shadows on the swirling oval below. The featured image has been processed to enhance color and contrast. Large ovals are usually regions of high pressure that span over 1000 kilometers and can last for years. The largest oval on Jupiter is the Great Red Spot (not pictured), which has lasted for at least hundreds of years. Studying cloud dynamics on Jupiter with Juno images enables a better understanding of dangerous typhoons and hurricanes on Earth.

APOD: 2021 October 26 - Jupiter Rotates
Explanation: Observe the graceful twirl of our Solar System's largest planet. Many interesting features of Jupiter's enigmatic atmosphere, including dark belts and light zones, can be followed in detail. A careful inspection will reveal that different cloud layers rotate at slightly different speeds. The famous Great Red Spot is not visible at first -- but soon rotates into view. Other smaller storm systems occasionally appear. As large as Jupiter is, it rotates in only 10 hours. Our small Earth, by comparison, takes 24 hours to complete a spin cycle. The featured high-resolution time-lapse video was captured over five nights earlier this month by a mid-sized telescope on an apartment balcony in Paris, France. Since hydrogen and helium gas are colorless, and those elements compose most of Jupiter's expansive atmosphere, what trace elements create the observed colors of Jupiter's clouds remains a topic of research.

APOD: 2021 October 11 - Juno Flyby of Ganymede and Jupiter
Explanation: What would it be like to fly over the largest moon in the Solar System? In June, the robotic Juno spacecraft flew past Jupiter's huge moon Ganymede and took images that have been digitally constructed into a detailed flyby. As the featured video begins, Juno swoops over the two-toned surface of the 2,000-km wide moon, revealing an icy alien landscape filled with grooves and craters. The grooves are likely caused by shifting surface plates, while the craters are caused by violent impacts. Continuing on in its orbit, Juno then performed its 34th close pass over Jupiter's clouds. The digitally-constructed video shows numerous swirling clouds in the north, colorful planet-circling zones and bands across the middle -- featuring several white-oval clouds from the String of Pearls, and finally more swirling clouds in the south. Next September, Juno is scheduled to make a close pass over another of Jupiter's large moons: Europa.

APOD: 2021 September 17 - Video: Flash on Jupiter
Explanation: There has been a flash on Jupiter. A few days ago, several groups monitoring our Solar System's largest planet noticed a two-second long burst of light. Such flashes have been seen before, with the most famous being a series of impactor strikes in 1994. Then, fragments of Comet Shoemaker-Levy 9 struck Jupiter leaving dark patches that lasted for months. Since then, at least seven impacts have been recorded on Jupiter -- usually discovered by amateur astronomers. In the featured video, variations in the Earth's atmosphere cause Jupiter's image to shimmer when, suddenly, a bright flash appears just left of center. Io and its shadow are visible on the right. What hit Jupiter will likely never be known, but considering what we do know of the nearby Solar System, it was likely a piece of rock and ice -- perhaps the size of a bus -- that broke off long-ago from a passing comet or asteroid.

APOD: 2021 June 8 - A Face in the Clouds of Jupiter from Juno
Explanation: What do you see in the clouds of Jupiter? On the largest scale, circling the planet, Jupiter has alternating light zones and reddish-brown belts. Rising zone gas, mostly hydrogen and helium, usually swirls around regions of high pressure. Conversely, falling belt gas usually whirls around regions of low pressure, like cyclones and hurricanes on Earth. Belt storms can form into large and long-lasting white ovals and elongated red spots. NASA's robotic Juno spacecraft captured most of these cloud features in 2017 during perijove 6, its sixth pass over the giant planet in its looping 2-month orbit. But it is surely not these clouds themselves that draws your attention to the displayed image, but rather their arrangement. The face that stands out, nicknamed Jovey McJupiterFace, lasted perhaps a few weeks before the neighboring storm clouds rotated away. Juno has now completed 33 orbits around Jupiter and just yesterday made a close pass near Ganymede, our Solar System's largest moon.

APOD: 2021 March 24 - Aurorae and Lightning on Jupiter
Explanation: Why does so much of Jupiter's lightning occur near its poles? Similar to Earth, Jupiter experiences both aurorae and lightning. Different from Earth, though, Jupiter's lightning usually occurs near its poles -- while much of Earth's lightning occurs near its equator. To help understand the difference, NASA's Juno spacecraft, currently orbiting Jupiter, has observed numerous aurora and lightning events. The featured image, taken by Juno's Stellar Reference Unit camera on 2018 May 24, shows Jupiter's northern auroral oval and several bright dots and streaks. An eye-catching event is shown in the right inset image -- which is a flash of Jupiter's lightning -- one of the closest images of aurora and lightning ever. On Earth (which is much nearer to the Sun than Jupiter), sunlight is bright enough to create, by itself, much stronger atmospheric heating at the equator than the poles, driving turbulence, storms, and lightning. On Jupiter, in contrast, atmospheric heating comes mostly from its interior (as a remnant from its formation), leading to the hypothesis that more intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

APOD: 2021 January 19 - A Lunar Corona with Jupiter and Saturn
Explanation: Why does a cloudy moon sometimes appear colorful? The effect, called a lunar corona, is created by the quantum mechanical diffraction of light around individual, similarly-sized water droplets in an intervening but mostly-transparent cloud. Since light of different colors has different wavelengths, each color diffracts differently. Lunar Coronae are one of the few quantum mechanical color effects that can be easily seen with the unaided eye. Solar coronae are also sometimes evident. The featured composite image was captured a few days before the close Great Conjunction between Saturn and Jupiter last month. In the foreground, the Italian village of Pieve di Cadore is visible in front of the Sfornioi Mountains.

APOD: 2020 December 30 - Jupiter and Saturn Great Conjunction: The Movie
Explanation: Yes, but have you seen a movie of Jupiter and Saturn's Great Conjunction? The featured time-lapse video was composed from a series of images taken from Thailand and shows the two giant planets as they angularly passed about a tenth of a degree from each other. The first Great Conjunction sequence shows a relative close up over five days with moons and cloud bands easily visible, followed by a second video sequence, zoomed out, over 9 days. Even though Jupiter and Saturn appeared to pass unusually close together on the sky on December 21, 2020, in actuality they were still nearly a billion kilometers apart. The two gas giants are destined for similar meet ups every 19.86 years. However, they had not come this close, angularly, for the past 397 years, and will not again for another 60 years. If you're willing to wait until the year 7541, though, you can see Jupiter pass directly in front of Saturn.

APOD: 2020 December 23 - Jupiter Meets Saturn: A Red Spotted Great Conjunction
Explanation: It was time for their close-up. Two days ago Jupiter and Saturn passed a tenth of a degree from each other in what is known a Great Conjunction. Although the two planets pass each other on the sky every 20 years, this was the closest pass in nearly four centuries. Taken early in day of the Great Conjunction, the featured multiple-exposure combination captures not only both giant planets in a single frame, but also Jupiter's four largest moons (left to right) Callisto, Ganymede, Io, and Europa -- and Saturn's largest moon Titan. If you look very closely, the clear Chilescope image even captures Jupiter's Great Red Spot. The now-separating planets can still be seen remarkably close -- within about a degree -- as they set just after the Sun, toward the west, each night for the remainder of the year.

APOD: 2020 December 15 - Great Conjunction: Saturn and Jupiter Converge
Explanation: It's happening. Saturn and Jupiter are moving closer and will soon appear in almost exactly the same direction. Coincidentally, on the night of the December solstice -- the longest night of the year in the north and the longest day in the south -- the long-awaited Great Conjunction will occur. Then, about six days from now, Saturn and Jupiter will be right next to each other -- as they are every 20 years. But this juxtaposition is not just any Great Conjunction -- it will be the closest since 1623 because the two planetary giants will pass only 1/10th of a degree from each other -- well less than the apparent diameter of a full moon. In the next few days a crescent moon will also pass a few degrees away from the converging planets and give a preliminary opportunity for iconic photos. The featured illustration shows the approach of Saturn and Jupiter during November and December over the French Alps.

APOD: 2020 December 12 - Saturn and Jupiter in Summer 2020
Explanation: During this northern summer Saturn and Jupiter were both near opposition, opposite the Sun in planet Earth's sky. Their paired retrograde motion, seen about every 20 years, is followed from 19 June through 28 August in this panoramic composite as they wander together between the stars in western Capricornus and eastern Sagittarius. But this December's skies find them drawing even closer together. Jupiter and Saturn are now close, bright celestial beacons in the west after sunset. On solstice day December 21 they will reach their magnificent 20 year Great Conjunction. Then the two largest worlds in the Solar System will appear in Earth's sky separated by only about 1/5 the apparent diameter of a Full Moon.

APOD: 2020 November 23 - A Jupiter Vista from Juno
Explanation: Why do colorful cloud bands encircle Jupiter? Jupiter's top atmospheric layer is divided into light zones and dark belts that go all the way around the giant planet. It is high horizontal winds -- in excess of 300 kilometers per hour -- that cause the zones to spread out planet-wide. What causes these strong winds remains a topic of research. Replenished by upwelling gas, zonal bands are thought to include relatively opaque clouds of ammonia and water that block light from lower and darker atmospheric levels. One light-colored zone is shown in great detail in the featured vista taken by the robotic Juno spacecraft in 2017. Jupiter's atmosphere is mostly clear and colorless hydrogen and helium, gases that are not thought to contribute to the gold and brown colors. What compounds create these colors is another active topic of research -- but is hypothesized to involve small amounts of sunlight-altered sulfur and carbon. Many discoveries have been made from Juno's data, including that water composes an unexpectedly high 0.25 percent of upper-level cloud molecules near Jupiter's equator, a finding important not only for understanding Jovian currents but for the history of water in the entire Solar System.

APOD: 2020 October 20 - Saturn and Jupiter over Italian Peaks
Explanation: Saturn and Jupiter are getting closer. Every night that you go out and check for the next two months, these two bright planets will be even closer together on the sky. Finally, in mid-December, a Great Conjunction will occur -- when the two planets will appear only 0.1 degrees apart -- just one fifth the angular diameter of the full Moon. And this isn't just any Great Conjunction -- Saturn (left) and Jupiter (right) haven't been this close since 1623, and won't be nearly this close again until 2080. This celestial event is quite easy to see -- already the two planets are easily visible toward the southwest just after sunset -- and already they are remarkably close. Pictured, the astrophotographer and partner eyed the planetary duo above the Tre Cime di Lavaredo (Three Peaks of Lavaredo) in the Italian Alps about two weeks ago.

APOD: 2020 October 19 - A Flight over Jupiter Near the Great Red Spot
Explanation: Are you willing to wait to see the largest and oldest known storm system in the Solar System? In the featured video, Jupiter's Great Red Spot finally makes its appearance 2 minutes and 12 seconds into the 5-minute video. Before it arrives, you may find it pleasing to enjoy the continually changing view of the seemingly serene clouds of Jupiter, possibly with your lights low and sound up. The 41 frames that compose the video were captured in June as the robotic Juno spacecraft was making a close pass over our Solar System's largest planet. The time-lapse sequence actually occurred over four hours. Since arriving at Jupiter in 2016, Juno's numerous discoveries have included unexpectedly deep atmospheric jet streams, the most powerful auroras ever recorded, and water-bearing clouds bunched near Jupiter's equator.

APOD: 2020 September 10 - Jupiter's Swimming Storm
Explanation: A bright storm head with a long turbulent wake swims across Jupiter in these sharp telescopic images of the Solar System's ruling gas giant. Captured on August 26, 28, and September 1 (left to right) the storm approximately doubles in length during that period. Stretching along the jetstream of the planet's North Temperate Belt it travels eastward in successive frames, passing the Great Red Spot and whitish Oval BA, famous storms in Jupiter's southern hemisphere. Galilean moons Callisto and Io are caught in the middle frame. In fact, telescopic skygazers following Jupiter in planet Earth's night have reported dramatic fast moving storm outbreaks over the past few weeks in Jupiter's North Temperate Belt.

APOD: 2020 September 2 - Jupiter and the Moons
Explanation: How many moons do you see? Many people would say one, referring to the Earth's Moon, prominent on the lower left. But take a closer look at the object on the upper right. That seeming-star is actually the planet Jupiter, and your closer look might reveal that it is not alone – it is surrounded by some of its largest moons. From left to right these Galilean Moons are Io, Ganymende, Europa and Callisto. These moons orbit the Jovian world just like the planets of our Solar System orbit the Sun, in a line when seen from the side. The featured single shot was captured from Cancun, Mexico last week as Luna, in its orbit around the Earth, glided past the distant planet. Even better views of Jupiter are currently being captured by NASA's Juno spacecraft, now in a looping orbit around the Solar System's largest planet. Earth's Moon will continue to pass nearly in front of both Jupiter and Saturn once a month (moon-th) as the two giant planets approach their own great conjunction in December.

APOD: 2020 August 13 - Jupiter and Saturn Rising Beyond Alien Throne Rock
Explanation: What planets are those behind that unusual rock spire? Saturn (lower left) and Jupiter.  This month, after sunset, the bright planetary duo are quite prominent toward the southeast.  Now your view of our Solar System's largest planets might not include a picturesque hoodoo in the foreground, nor the spectacular central band of our Milky Way Galaxy across the background, but should be quite eye-catching anyway.  The featured image is a composite of consecutive foreground and background exposures all taken in late May with the same camera and from the same location -- the badlands of the  Ah-Shi-Sle-Pah Wilderness in the San Juan Basin in New Mexico, USA.  The rock spire, informally dubbed 'Alien Throne', stands about 3 meters tall. Saturn and Jupiter will remain visible together after sunset for several months.

APOD: 2020 August 11 - Churning Clouds on Jupiter
Explanation: Where is Jupiter's ammonia? Gaseous ammonia was expected to be seen in Jupiter's upper atmosphere by the orbiting Juno spacecraft -- but in many clouds is almost absent. Recent Juno data, however, gives some clues: some high-level clouds appear to be home to an unexpected type of electrical discharge dubbed shallow lightning. Great charge separations are needed for lightning, which might be created by colliding mushballs lifted by rising updrafts of gas. Ammonia and water stick to these mushballs which rise until they get too heavy -- after which they fall deep into Jupiter's atmosphere and melt. By this process, ammonia found missing from Jupiter's upper atmosphere reappears below. Pictured by Juno, churning clouds on Jupiter show not only mesmerizing complexity but some high-level, light-colored pop-up clouds. Understanding atmospheric dynamics on Jupiter gives valuable perspective to similar atmospheric and lightning phenomena that occur on our home Earth.

APOD: 2020 June 28 - Europa and Jupiter from Voyager 1
Explanation: What are those spots on Jupiter? Largest and furthest, just right of center, is the Great Red Spot -- a huge storm system that has been raging on Jupiter possibly since Giovanni Cassini's likely notation of it 355 years ago. It is not yet known why this Great Spot is red. The spot toward the lower left is one of Jupiter's largest moons: Europa. Images from Voyager in 1979 bolster the modern hypothesis that Europa has an underground ocean and is therefore a good place to look for extraterrestrial life. But what about the dark spot on the upper right? That is a shadow of another of Jupiter's large moons: Io. Voyager 1 discovered Io to be so volcanic that no impact craters could be found. Sixteen frames from Voyager 1's flyby of Jupiter in 1979 were recently reprocessed and merged to create the featured image. About 43 years ago, Voyager 1 launched from Earth and started one of the greatest explorations of the Solar System ever.

APOD: 2020 May 13 - Jupiter in Infrared from Gemini
Explanation: In infrared, Jupiter lights up the night. Recently, astronomers at the Gemini North Observatory in Hawaii, USA, created some of the best infrared photos of Jupiter ever taken from Earth’s surface, pictured. Gemini was able to produce such a clear image using a technique called lucky imaging, by taking many images and combining only the clearest ones that, by chance, were taken when Earth's atmosphere was the most calm. Jupiter’s jack-o’-lantern-like appearance is caused by the planet’s different layers of clouds. Infrared light can pass through clouds better than visible light, allowing us to see deeper, hotter layers of Jupiter's atmosphere, while the thickest clouds appear dark. These pictures, together with ones from the Hubble Space Telescope and the Juno spacecraft, can tell us a lot about weather patterns on Jupiter, like where its massive, planet-sized storms form.

APOD: 2020 February 25 - Jupiter's Magnetic Field from Juno
Explanation: How similar is Jupiter's magnetic field to Earth's? NASA's robotic Juno spacecraft has found that Jupiter's magnetic field is surprisingly complex, so that the Jovian world does not have single magnetic poles like our Earth. A snapshot of Jupiter's magnetic field at one moment in time, as animated from Juno data, appears in the featured video. Red and blue colors depict cloud-top regions of strong positive (south) and negative (north) magnetic fields, respectively. Surrounding the planet are imagined magnetic field lines. The first sequence of the animated video starts off by showing what appears to be a relatively normal dipole field, but soon a magnetic region now known as the Great Blue Spot rotates into view, which is not directly aligned with Jupiter's rotation poles. Further, in the second sequence, the illustrative animation takes us over one of Jupiter's spin poles where red magnetic hotspots are revealed to be extended and sometimes even annular. A better understanding of Jupiter's magnetic field may give clues toward a better understanding of Earth's enigmatic planetary magnetism.

APOD: 2020 January 6 - Tumultuous Clouds of Jupiter
Explanation: Some cloud patterns on Jupiter are quite complex. The featured tumultuous clouds were captured in May by NASA's robotic Juno spacecraft currently orbiting our Solar System's largest planet. The image was taken when Juno was only about 15,000 kilometers over Jupiter's cloud tops, so close that less than half of the giant planet is visible. The rough white clouds on the far right are high altitude clouds known as pop-up clouds. Juno's mission, now extended into 2021, is to study Jupiter in new ways. Among many other things, Juno has been measuring Jupiter's gravitational field, finding surprising evidence that Jupiter may be mostly a liquid.

APOD: 2019 November 26 - Venus and Jupiter on the Horizon
Explanation: What are those two bright objects on the horizon? Venus and Jupiter. The two brightest planets in the night sky passed very close together -- angularly -- just two days ago. In real space, they were just about as far apart as usual, since Jupiter (on the right) orbits the Sun around seven times farther out than Venus. The planetary duo were captured together two days ago in a picturesque sunset sky from Llers, Catalonia, Spain between a tree and the astrophotographer's daughter. These two planets will continue to stand out in the evening sky, toward the west, for the next few days, with a sliver of a crescent Moon and a fainter Saturn also visible nearby. As November ends, Jupiter will sink lower into the sunset horizon with each subsequent night, while Venus will rise higher. The next Jupiter-Venus conjunction will occur in early 2021.

APOD: 2019 October 7 - Io Eclipse Shadow on Jupiter from Juno
Explanation: What's that dark spot on Jupiter? It's the shadow of Jupiter's most volcanic moon Io. Since Jupiter shines predominantly by reflected sunlight, anything that blocks that light leaves a shadow. If you could somehow be in that shadow, you would see a total eclipse of the Sun by Io. Io's shadow is about 3600 kilometers across, roughly the same size as Io itself -- and only slightly larger than Earth's Moon. The featured image was taken last month by NASA's robotic Juno spacecraft currently orbiting Jupiter. About every two months, Juno swoops close by Jupiter, takes a lot of data and snaps a series of images -- some of which are made into a video. Among many other things, Juno has been measuring Jupiter's gravitational field, finding surprising evidence that Jupiter may be mostly a liquid. Under unexpectedly thick clouds, the Jovian giant may house a massive liquid hydrogen region that extends all the way to the center.

APOD: 2019 October 5 - Jupiter and the Moons
Explanation: After sunset on October 3, some of the Solar System's largest moons stood low along the western horizon with the largest planet. Just after nightfall, a pairing of the Moon approaching first quarter phase and Jupiter was captured in this telephoto field of view. A blend of short and long exposures, it reveals the familiar face of our fair planet's own large natural satellite in stark sunlight and faint earthshine. At lower right are the ruling gas giant and its four Galilean moons. Left to right, the tiny pinpricks of light are Ganymede, [Jupiter], Io, Europa, and Callisto. Our own natural satellite appears to loom large because it's close, but Ganymede, Io, and Callisto are actually larger than Earth's Moon. Water world Europa is only slightly smaller. Of the Solar System's six largest planetary satellites, only Saturn's moon Titan, is missing from this scene. But be sure to check for large moons in your sky tonight.

APOD: 2019 September 8 - Perijove 11: Passing Jupiter
Explanation: Here comes Jupiter! NASA's robotic spacecraft Juno is continuing on its 53-day, highly-elongated orbits around our Solar System's largest planet. The featured video is from perijove 11 in early 2018, the eleventh time Juno has passed near Jupiter since it arrived in mid-2016. This time-lapse, color-enhanced movie covers about four hours and morphs between 36 JunoCam images. The video begins with Jupiter rising as Juno approaches from the north. As Juno reaches its closest view -- from about 3,500 kilometers over Jupiter's cloud tops -- the spacecraft captures the great planet in tremendous detail. Juno passes light zones and dark belt of clouds that circle the planet, as well as numerous swirling circular storms, many of which are larger than hurricanes on Earth. After the perijove, Jupiter recedes into the distance, now displaying the unusual clouds that appear over Jupiter's south. To get desired science data, Juno swoops so close to Jupiter that its instruments are exposed to very high levels of radiation.

APOD: 2019 September 2 - The Moon and Jupiter over the Alps
Explanation: What are those bright lights in the sky ahead? When hiking a high mountain pass in northern Italy three weeks ago, a conjunction between our Moon and the distant planet Jupiter was visible toward the south just after sunset. The picturesque mountains in the distance are Tre Cime di Lavaredo (Three Peaks of Lavaredo), a UNESCO World Heritage Site and three of the best known mountain peaks in Italy, the Dolomites, and the entire Alps. In the foreground on the left is Locatelli Hut, a refuge for tired hikers as it is located over an hour from nearest parking lot. The bright sky object on the upper left is Saturn. The entire scene was captured on a single 8-second exposure. Jupiter and Saturn will remain prominent in the southwestern sky after sunset this month, while the Moon, in its monthly orbit around the Earth, will pass near Jupiter again in about four days.

APOD: 2019 August 7 - Jupiter Engulfed and the Milky Way
Explanation: This is a good month to see Jupiter. To find our Solar System's largest planet in your sky, look toward the southeast just after sunset -- Jupiter should be the brightest object in that part of the sky. If you have a binoculars or a small telescope, you should be able to see Jupiter's four brightest moons right nearby, and possibly some cloud bands. The featured image was taken about a month ago from the Persian Gulf. The image shows Jupiter just to the right of the nearly vertical band of the central disk of our Milky Way Galaxy. The unnamed rock formations appear in projection like the jaws of a giant monster ready to engulf the Jovian giant. When you see Jupiter, it may be interesting to know that NASA's robotic Juno spacecraft is simultaneously visiting and studying the giant planet. Saturn is also visible this month, and although it is nearby to Jupiter, it is not as bright.

APOD: 2019 June 10 - Jupiter Abyss
Explanation: What's that black spot on Jupiter? No one is sure. During the latest pass of NASA's Juno around Jupiter, the robotic spacecraft imaged an usually dark cloud feature informally dubbed the Abyss. Surrounding cloud patterns show the Abyss to be at the center of a vortex. Since dark features on Jupiter's atmosphere tend to run deeper than light features, the Abyss may really be the deep hole that it appears -- but without more evidence that remains conjecture. The Abyss is surrounded by a complex of meandering clouds and other swirling storm systems, some of which are topped by light colored, high-altitude clouds. The featured image was captured last month while Juno passed only about 15,000 kilometers above Jupiter's cloud tops. The next close pass of Juno near Jupiter will be in July.

APOD: 2019 May 23 - Moons Near Jupiter
Explanation: On May 20, a nearly Full Moon and Jupiter shared this telephoto field of view. Captured when a passing cloud bank dimmed the moonlight, the single exposure reveals the familiar face of our fair planet's own large natural satellite, along with bright Jupiter (lower right) and some of its Galilean moons. Lined up left to right the tiny pinpricks of light near Jupiter are Ganymede, Europa, [Jupiter] and Callisto. (That's not just dust on your screen ...) Closer and brighter, our own natural satellite appears to loom large. But Ganymede, and Callisto are physically larger than Earth's Moon, while water world Europa is only slightly smaller. In fact, of the Solar System's six largest planetary satellites, Saturn's moon Titan is missing from the scene and a fourth Galilean moon, Io, is hidden by our ruling gas giant.

APOD: 2019 May 8 - Jupiter Marble from Juno
Explanation: What does Jupiter look like up close? Most images of Jupiter are taken from far away, either from Earth or from a great enough distance that nearly half the planet is visible. This shot, though, was composed from images taken relatively close in, where less than half of the planet was visible. From here, Jupiter still appears spherical but perspective distortion now makes it look more like a marble. Visible on Jupiter's cloud tops are a prominent dark horizontal belt containing a white oval cloud, and a white zone cloud, both of which circle the planet. The Great Red Spot looms on the upper right. The featured image was taken by the robotic Juno spacecraft in February during its 17th close pass of our Solar System's largest planet. Juno's mission, now extended into 2021, is to study Jupiter in new ways. Juno's data has already enabled discoveries that include Jupiter's magnetic field being surprisingly lumpy, and that some of Jupiter's cloud systems run about 3,000 kilometers into the planet.

APOD: 2019 April 15 - Enhanced: The Dolphin Cloud on Jupiter
Explanation: Do you see the dolphin-shaped cloud on Jupiter? The cloud was visible last year during perijove 16, the sixteenth time that NASA's robotic spacecraft Juno passed near Jupiter since it arrived in mid-2016. During each perijove, Juno passes near a slightly different part of Jupiter's cloud tops. The dolphin shape may be surprising but is not scientifically significant -- clouds on Jupiter and Earth are constantly shifting and can temporarily mimic many familiar shapes. The cloud appears in Jupiter's South Temperate Belt (STB), a band of dark and dropping clouds that rings the planet and also contains Oval BA, dubbed Red Spot Jr. The featured image was digitally processed to enhance color and contrast. Juno's next swoop near Jupiter -- perijove 20 -- will occur on late May.

APOD: 2019 February 5 - Perijove 16: Passing Jupiter
Explanation: Watch Juno zoom past Jupiter again. NASA's robotic spacecraft Juno is continuing on its 53-day, highly-elongated orbits around our Solar System's largest planet. The featured video is from perijove 16, the sixteenth time that Juno has passed near Jupiter since it arrived in mid-2016. Each perijove passes near a slightly different part of Jupiter's cloud tops. This color-enhanced video has been digitally composed from 21 JunoCam still images, resulting in a 125-fold time-lapse. The video begins with Jupiter rising as Juno approaches from the north. As Juno reaches its closest view -- from about 3,500 kilometers over Jupiter's cloud tops -- the spacecraft captures the great planet in tremendous detail. Juno passes light zones and dark belt of clouds that circle the planet, as well as numerous swirling circular storms, many of which are larger than hurricanes on Earth. As Juno moves away, the remarkable dolphin-shaped cloud is visible. After the perijove, Jupiter recedes into the distance, now displaying the unusual clouds that appear over Jupiter's south. To get desired science data, Juno swoops so close to Jupiter that its instruments are exposed to very high levels of radiation.

APOD: 2018 November 21 - Swirls and Colors on Jupiter from Juno
Explanation: What creates the colors in Jupiter's clouds? No one is sure. The thick atmosphere of Jupiter is mostly hydrogen and helium, elements which are colorless at the low temperatures of the Jovian cloud tops. Which trace elements provide the colors remains a topic of research, although small amounts of ammonium hydrosulfide are one leading candidate. What is clear from the featured color-enhanced image -- and many similar images -- is that lighter clouds are typically higher up than darker ones. Pictured, light clouds swirl around reddish regions toward the lower right, while they appear to cover over some darker domains on the upper right. The featured image was taken by the robotic Juno spacecraft during its 14th low pass over Jupiter earlier this year. Juno continues in its looping elliptical orbit, swooping near the huge planet every 53 days and exploring a slightly different sector each time around.

APOD: 2018 October 16 - Jupiter in Ultraviolet from Hubble
Explanation: Jupiter looks a bit different in ultraviolet light. To better interpret Jupiter's cloud motions and to help NASA's robotic Juno spacecraft understand the planetary context of the small fields that it sees, the Hubble Space Telescope is being directed to regularly image the entire Jovian giant. The colors of Jupiter being monitored go beyond the normal human visual range to include both ultraviolet and (not pictured) infrared light. Featured from 2017, Jupiter appears different in near ultraviolet light, partly because the amount of sunlight reflected back is distinct, giving differing cloud heights and latitudes discrepant brightnesses. In the near UV, Jupiter's poles appear relatively dark, as does its Great Red Spot and a smaller (optically) white oval to the right. The String of Pearl storms farther to the right, however, are brightest in near ultraviolet, and so here appear (false-color) pink. Jupiter's largest moon Ganymede appears on the upper left. Juno continues on its looping 53-day orbits around Jupiter, while Earth-orbiting Hubble is now recovering from the loss of a stabilizing gyroscope.

APOD: 2018 June 5 - Complex Jupiter
Explanation: How complex is Jupiter? NASA's Juno mission to Jupiter is finding the Jovian giant to be more complicated than expected. Jupiter's magnetic field has been discovered to be much different from our Earth's simple dipole field, showing several poles embedded in a complicated network more convoluted in the north than the south. Further, Juno's radio measurements show that Jupiter's atmosphere shows structure well below the upper cloud deck -- even hundreds of kilometers deep. Jupiter's newfound complexity is evident also in southern clouds, as shown in the featured image. There, planet-circling zones and belts that dominate near the equator decay into a complex miasma of continent-sized storm swirls. Juno continues in its looping elliptical orbit, swooping near the huge planet every 53 days and exploring a slightly different sector each time around.

APOD: 2018 May 21 - Jupiter Cloud Animation from Juno
Explanation: How do Jupiter's clouds move? To help find out, images taken with NASA's Juno spacecraft during its last pass near Jupiter have been analyzed and digitally extrapolated into a time-lapse video. The eight-second time-lapse video, digitally extrapolated between two images taken only nine minutes apart, estimates how Jupiter's clouds move over 29 hours. Abstractly, the result appears something like a psychedelic paisley dream. Scientifically, however, the computer animation shows that circular storms tend to swirl, while bands and zones appear to flow. This overall motion is not surprising and has been seen on time-lapse videos of Jupiter before, although never in this detail. The featured region spans about four times the area of Jupiter's Great Red Spot. Results from Juno are showing, unexpectedly, that Jupiter's weather phenomena can extend deep below its cloud tops.

APOD: 2018 April 25 - Hubble's Jupiter and the Shrinking Great Red Spot
Explanation: What will become of Jupiter's Great Red Spot? Gas giant Jupiter is the solar system's largest world with about 320 times the mass of planet Earth. Jupiter is home to one of the largest and longest lasting storm systems known, the Great Red Spot (GRS), visible to the left. The GRS is so large it could swallow Earth, although it has been shrinking. Comparison with historical notes indicate that the storm spans only about one third of the surface area it had 150 years ago. NASA's Outer Planets Atmospheres Legacy (OPAL) program has been monitoring the storm more recently using the Hubble Space Telescope. The featured Hubble OPAL image shows Jupiter as it appeared in 2016, processed in a way that makes red hues appear quite vibrant. Modern GRS data indicate that the storm continues to constrict its surface area, but is also becoming slightly taller, vertically. No one knows the future of the GRS, including the possibility that if the shrinking trend continues, the GRS might one day even do what smaller spots on Jupiter have done -- disappear completely.

APOD: 2018 April 16 - Flyover of Jupiter's North Pole in Infrared
Explanation: What would it look like to fly over the North Pole of Jupiter? A fictional animation made from real images and data captured by NASA's Juno spacecraft shows an answer. Since the pole is presently in shadow, the video uses infrared light emitted by Jupiter -- specifically an infrared color where the hottest features glows the brightest. As the animation starts, Juno zooms in on the enormous world. Soon, one of the eight cyclones orbiting the North Pole is featured. One by one, all eight cyclones circling the pole are inspected, each the size of an entire continent on Earth, and each containing bumpy and fragmented spiral walls. The virtual trip ends with a zoom out. Studying Jovian cyclones helps humanity to better understand dangerous storm systems that occur here on Earth. Juno has recently concluded another close pass by Jupiter -- Perijove 12 -- and seems healthy enough to complete several more of the two-month orbits.

APOD: 2018 March 8 - Cyclones at Jupiter s North Pole
Explanation: Juno's Jovian Infrared Auroral Mapper data was used to construct this stunning view of cyclones at Jupiter's North Pole. Measuring the thermal emission from Jovian cloud tops, the infrared observations are not restricted to the hemisphere illuminated by sunlight. They reveal eight cyclonic features that surround a cyclone about 4,000 kilometers in diameter, just offset from the giant planet's geographic North Pole. Similar data show a cyclone at the Jovian South Pole with five circumpolar cyclones. The South Pole cyclones are slightly larger than their northern cousins. Cassini data has shown that gas giant Saturn's north and south poles each have a single cyclonic storm system.

APOD: 2018 February 26 - Passing Jupiter
Explanation: Here comes Jupiter! NASA's robotic spacecraft Juno is continuing on its 53-day, highly-elongated orbits around our Solar System's largest planet. The featured video is from perijove 11, the eleventh time Juno has passed near Jupiter since it arrived in mid-2016. This time-lapse, color-enhanced movie covers about four hours and morphs between 36 JunoCam images. The video begins with Jupiter rising as Juno approaches from the north. As Juno reaches its closest view -- from about 3,500 kilometers over Jupiter's cloud tops -- the spacecraft captures the great planet in tremendous detail. Juno passes light zones and dark belt of clouds that circle the planet, as well as numerous swirling circular storms, many of which are larger than hurricanes on Earth. After the perijove, Jupiter recedes into the distance, now displaying the unusual clouds that appear over Jupiter's south. To get desired science data, Juno swoops so close to Jupiter that its instruments are exposed to very high levels of radiation.

APOD: 2018 February 21 - Jupiter in Infrared from Hubble
Explanation: Jupiter looks a bit different in infrared light. To better understand Jupiter's cloud motions and to help NASA's robotic Juno spacecraft understand the planetary context of the small fields that it sees, the Hubble Space Telescope is being directed to regularly image the entire Jovian giant. The colors of Jupiter being monitored go beyond the normal human visual range to include both ultraviolet and infrared light. Featured here in 2016, three bands of near-infrared light have been digitally reassigned into a mapped color image. Jupiter appears different in infrared partly because the amount of sunlight reflected back is distinct, giving differing cloud heights and latitudes discrepant brightnesses. Nevertheless, many familiar features on Jupiter remain, including the light zones and dark belts that circle the planet near the equator, the Great Red Spot on the lower left, and the string-of-pearls storm systems south of the Great Red Spot. The poles glow because high altitude haze there is energized by charged particles from Jupiter's magnetosphere. Juno has now completed 10 of 12 planned science orbits of Jupiter and continues to record data that are helping humanity to understand not only Jupiter's weather but what lies beneath Jupiter's thick clouds.

APOD: 2017 December 14 - Jupiter Diving
Explanation: Take this simulated plunge and dive into the upper atmosphere of Jupiter, the Solar System's ruling gas giant. The awesome animation is based on image data from JunoCam, and the microwave radiometer on board the Jupiter-orbiting Juno spacecraft. Your view will start about 3,000 kilometers above the southern Jovian cloud tops, but you can track your progress on the display at the left. As altitude decreases, temperature increases while you dive deeper at the location of Jupiter's famous Great Red Spot. In fact, Juno data indicates the Great Red Spot, the Solar System's largest storm system, penetrates some 300 kilometers into the giant planet's atmosphere. For comparison, the deepest point for planet Earth's oceans is just under 11 kilometers down. Don't panic though, you'll fly back out again.

APOD: 2017 November 28 - Juno Spots a Complex Storm on Jupiter
Explanation: Some storms on Jupiter are quite complex. The swirling storm was captured late last month by the NASA's robotic Juno spacecraft currently orbiting the Solar System's largest planet. The featured image spans about 30,000 kilometers, making this storm system just about as wide as planet Earth. The disturbance rotates counter-clockwise and shows a cloud pattern that includes light-colored updrafts thought to be composed predominantly of ammonia ice. These light clouds are the highest up and even cast discernable shadows toward the right. Juno will continue to orbit and probe Jupiter over the next few years as it tries to return data that help us to better understand Jupiter's atmospheric water abundance and if the planet has a solid surface underneath these fascinating clouds.

APOD: 2017 September 5 - Europa and Jupiter from Voyager 1
Explanation: What are those spots on Jupiter? Largest and furthest, just right of center, is the Great Red Spot -- a huge storm system that has been raging on Jupiter possibly since Giovanni Cassini's likely notation of it 352 years ago. It is not yet known why this Great Spot is red. The spot toward the lower left is one of Jupiter's largest moons: Europa. Images from Voyager in 1979 bolster the modern hypothesis that Europa has an underground ocean and is therefore a good place to look for extraterrestrial life. But what about the dark spot on the upper right? That is a shadow of another of Jupiter's large moons: Io. Voyager 1 discovered Io to be so volcanic that no impact craters could be found. Sixteen frames from Voyager 1's flyby of Jupiter in 1979 were recently reprocessed and merged to create the featured image. Forty years ago today, Voyager 1 launched from Earth and started one of the greatest explorations of the Solar System ever.

APOD: 2017 June 7 - Orbiting Jupiter
Explanation: What would it be like to orbit Jupiter? The dramatic featured video depicts just this and was made from images taken by NASA's Juno spacecraft currently orbiting the Jovian giant. Juno recently completed its sixth pass near Jupiter during its looping elliptical six-week orbit. As the time-lapse video starts, alternating dark and light cloud bands passed underneath the spacecraft as it approaches Jupiter's South Pole. These clouds contain complex textures involving eddies, swirls, ovals, and extended clouds that have no direct analog from Earth. As the spacecraft passes beneath Jupiter, new cloud patterns devoid of long bands emerge but are again rich with alien swirls and ovals. Over the next few years, Juno will continue to orbit and probe Jupiter, determine atmospheric water abundance, and attempt to determine if Jupiter has a solid surface underneath these fascinating clouds.

APOD: 2017 May 29 - Beneath Jupiter
Explanation: Jupiter is stranger than we knew. NASA's Juno spacecraft has now completed its sixth swoop past Jupiter as it moves around its highly elliptical orbit. Pictured, Jupiter is seen from below where, surprisingly, the horizontal bands that cover most of the planet disappear into swirls and complex patterns. A line of white oval clouds is visible nearer to the equator. Recent results from Juno show that Jupiter's weather phenomena can extend deep below its cloud tops, and that Jupiter's magnetic field varies greatly with location. Juno is scheduled to orbit Jupiter 37 times with each orbit taking about six weeks.

APOD: 2017 May 23 - Approaching Jupiter
Explanation: What would it look like to approach Jupiter? To help answer this, a team of 91 amateur astrophotographers took over 1,000 pictures of Jupiter from the Earth with the resulting images aligned and digitally merged into the featured time-lapse video. Image taking began in 2014 December and lasted just over three months. The resulting fictitious approach sequence has similarities to what was seen by NASA's robotic Juno spacecraft as it first approached the Jovian world last July. The video begins with Jupiter appearing as a small orb near the image center. As Jupiter nears from below, the planet looms ever larger while the rotation of its cloud bands becomes apparent. Jupiter's shrinking Great Red Spot rotates into view twice, at times showing unusual activity. Many white ovals are visible moving around the giant planet. The video ends as the imaginary spacecraft passes over Jupiter's North Pole.

APOD: 2017 April 13 - Moons and Jupiter
Explanation: On April 10, a Full Moon and Jupiter shared this telephoto field of view. Both were near opposition, opposite the Sun in Earth's night sky. Captured when a passing cloud bank dimmmed the bright moonlight, the single exposure reveals the familiar face of our fair planet's own large natural satellite, along with a line up of the ruling gas giant's four Galilean moons. Labeled top to bottom, the tiny pinpricks of light above bright Jupiter are Callisto, Europa, Ganymede, and Io. Closer and brighter, our own natural satellite appears to loom large. But Callisto, Ganymede, and Io are physically larger than Earth's Moon, while water world Europa is only slightly smaller. In fact, of the Solar System's six largest planetary satellites, only Saturn's moon Titan is missing from the scene.

APOD: 2017 February 28 - A White Oval Cloud on Jupiter from Juno
Explanation: This storm cloud on Jupiter is almost as large as the Earth. Known as a white oval, the swirling cloud is a high pressure system equivalent to an Earthly anticyclone. The cloud is one of a "string of pearls" ovals south of Jupiter's famous Great Red Spot. Possibly, the Great Red Spot is just a really large white oval that turned red. Surrounding clouds show interesting turbulence as they flow around and past the oval. The featured image was captured on February 2 as NASA's robotic spacecraft Juno made a new pass just above the cloud tops of the Jovian world. Over the next few years, Juno will continue to orbit and probe Jupiter, determine atmospheric water abundance, and attempt to determine if Jupiter has a solid surface beneath its thick clouds.

APOD: 2017 February 13 - Cloud Swirls around Southern Jupiter from Juno
Explanation: Juno just completed its fourth pass near Jupiter. Launched from Earth in 2011 and arriving at Jupiter just last July, robotic Juno concluded its latest elliptical orbit around our Solar System's largest planet 11 days ago. Pictured here from that pass is a new high-resolution image of the southern hemisphere of Jupiter featuring a mesmerizing tapestry of swirling cloud systems. The terminator between day and night cuts diagonally across the bottom, meaning that the Sun is positioned off the top right. Large Oval BA is visible in orange on the far right. Reasons for the details and colors of Jupiter's cloud swirls are currently unknown. Juno's planned six year mission will study Jovian giant in new ways, including trying to determine if beneath its thick clouds, Jupiter has a solid core.

APOD: 2016 December 17 - Southern Jupiter from Perijove 3
Explanation: Southern Jupiter looms some 37,000 kilometers away in this JunoCam image from December 11. The image data was captured near Juno's third perijove or closest approach to Jupiter, the spacecraft still in its 53 day long looping orbit. With the south polar region on the left, the large whitish oval toward the right is massive, counterclockwise rotating storm system. Smaller than the more famous Great Red Spot, the oval storm is only about half the diameter of planet Earth, one of a string of white ovals currently in the southern hemisphere of the Solar System's, ruling gas giant.

APOD: 2016 December 6 - Aurora over Jupiter's South Pole from Juno
Explanation: Why is there a glowing oval over Jupiter's South Pole? Aurora. Near the closest part of its first pass near Jupiter in August, NASA's robotic spacecraft Juno captured this dramatic infrared image of a bright auroral ring. Auroras are caused by high energy particles from the Sun interacting with a planet's magnetic field, and ovals around magnetic poles are common. Data from Juno are giving preliminary indications that Jupiter's magnetic field and aurorae are unexpectedly powerful and complex. Unfortunately, a computer glitch caused Juno to go into safe mode during its October pass near the Jovian giant in October. That glitch has now been resolved, making Juno ready for its next pass over Jupiter's cloud tops this coming Sunday.

APOD: 2016 October 25 - Clouds Near Jupiter's South Pole from Juno
Explanation: What's happening near the south pole of Jupiter? Recent images sent back by NASA's robotic Juno spacecraft are showing an interesting conglomeration of swirling clouds and what appear to be white ovals. Juno arrived at Jupiter in July and is being placed into a wide, looping orbit that will bring it near the gas giant -- and over its poles -- about twice a month. The featured image is a composite taken by JunoCam and post-processed by a digitally savvy citizen scientist. White ovals have been observed elsewhere on Jupiter and are thought to be giant storm systems. They have been observed to last for years, while typically showing Category 5 wind speeds of around 350 kilometers per hour. Unlike Earthly cyclones and hurricanes where high winds circle regions of low pressure, white ovals on Jupiter show rotational directions indicating that they are anticylones -- vortices centered on high pressure regions. Juno will continue to orbit Jupiter over thirty more times while recording optical, spectral, and gravitational data meant to help determine Jupiter's structure and evolution.

APOD: 2016 September 27 - Jupiter's Europa from Spacecraft Galileo
Explanation: What mysteries might be solved by peering into this crystal ball? In this case, the ball is actually a moon of Jupiter, the crystals are ice, and the moon is not only dirty but cracked beyond repair. Nevertheless, speculation is rampant that oceans exist under Europa's fractured ice-plains that could support life. This speculation was bolstered again this week by released images from the Hubble Space Telescope indicating that plumes of water vapor sometimes emanate from the ice-crusted moon -- plumes that might bring microscopic sea life to the surface. Europa, roughly the size of Earth's Moon, is pictured here in natural color as photographed in 1996 by the now-defunct Jupiter-orbiting Galileo spacecraft. Future observations by Hubble and planned missions such as the James Webb Space Telescope later this decade and a Europa flyby mission in the 2020s may further humanity's understanding not only of Europa and the early Solar System but also of the possibility that life exists elsewhere in the universe.

APOD: 2016 September 14 - The North and South of Jupiter
Explanation: A wide, looping orbit brought Juno close to Jupiter on August 27. As the spacecraft swung around the giant planet's poles JunoCam acquired these premier direct polar views, a change from the usual nearly equatorial perspective of outbound spacecraft and the telescopes of planet Earth. The sunlit side of Jupiter's north polar region (left) was imaged about 125,000 kilometers from the cloud tops, two hours before Juno's closest approach. An hour after close approach the south polar region was captured from 94,500 kilometers away. Strikingly different from the alternating light-colored zones and darker belts girdling more familiar equatorial regions, the polar region clouds appear more convoluted and mottled by many clockwise and counterclockwise rotating storm systems. Another 35 close orbital flybys are planned during the Juno mission.

APOD: 2016 September 4 - Io over Jupiter from Voyager 1
Explanation: Back in 1979, NASA's Voyager 1 spacecraft flew past Jupiter and its moons. The images in this mosaic, featuring the moon Io against a background of gas giant Jupiter's diffuse swirling cloud bands, were recorded by Voyager's camera from a distance of about 8.3 million kilometers. The Io image from this mosaic may be the first to show curious round features on Io's surface with dark centers and bright rims more than 60 kilometers across. Now known to be volcanic in origin, these features were then thought likely to be impact craters, commonly seen on rocky bodies throughout the Solar System. But as Voyager continued to approach Io, close-up pictures revealed a bizarre world devoid of impact craters, frequently resurfaced by volcanic activity. Earlier this year a new robotic spacecraft, NASA's Juno, began to orbit Jupiter and last week made a pass within 5,000 kilometers of Jupiter's clouds. During the next two years, it is hoped that Juno will discover new things about Jupiter, for example what's in Jupiter's core.

APOD: 2016 August 7 - Io: Moon over Jupiter
Explanation: How big is Jupiter's moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the featured picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. In July, NASA's Juno satellite began orbiting Jupiter and will sometimes swoop to within 5,000 kilometers of Jupiter's cloud tops.

APOD: 2016 July 11 - Aurorae on Jupiter
Explanation: Jupiter has aurorae. Like Earth, the magnetic field of the gas giant funnels charged particles released from the Sun onto the poles. As these particles strike the atmosphere, electrons are temporarily knocked away from existing gas molecules. Electric force attracts these electrons back. As the electrons recombine to remake neutral molecules, auroral light is emitted. In the featured recently released composite image by the Hubble Space Telescope taken in ultraviolet light, the aurorae appear as annular sheets around the pole. Unlike Earth's aurorae, Jupiter's aurorae include several bright streaks and dots. Jupiter's Great Red Spot is visible on the lower right. Recent aurorae on Jupiter have been particularly strong -- a fortunate coincidence with the arrival of NASA's Juno spacecraft at Jupiter last week. Juno was able to monitor the Solar Wind as it approached Jupiter, enabling a better understanding of aurorae in general, including on Earth.

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

APOD: 2016 July 1 - Juno Approaching Jupiter
Explanation: Approaching over the north pole after nearly a five-year journey, Juno enjoys a perspective on Jupiter not often seen, even by spacecraft from Earth that usually swing by closer to Jupiter's equator. Looking down toward the ruling gas giant from a distance of 10.9 million kilometers, the spacecraft's JunoCam captured this image with Jupiter's nightside and orbiting entourage of four large Galilean moons on June 21. JunoCam is intended to provide close-up views of the gas giant's cloudy zoned and belted atmosphere. On July 4 (July 5 UT) Juno is set to burn its main engine to slow down and be captured into its own orbit around the giant planet. If all goes well, it will be the first spacecraft to orbit the poles of Jupiter, skimming to within 5,000 kilometers of the Jovian cloud tops during the 20 month mission.

APOD: 2016 June 26 - Jupiter's Clouds from New Horizons
Explanation: The New Horizons spacecraft took some stunning images of Jupiter on its way out to Pluto. Famous for its Great Red Spot, Jupiter is also known for its regular, equatorial cloud bands, visible through even modest sized telescopes. The featured image, horizontally compressed, was taken in 2007 near Jupiter's terminator and shows the Jovian giant's wide diversity of cloud patterns. On the far left are clouds closest to Jupiter's South Pole. Here turbulent whirlpools and swirls are seen in a dark region, dubbed a belt, that rings the planet. Even light colored regions, called zones, show tremendous structure, complete with complex wave patterns. The energy that drives these waves surely comes from below. New Horizons is the fastest space probe ever launched, has successfully complete its main flyby of Pluto in 2015, and is now heading further out and on track to flyby Kuiper belt object 2014 MU69 in 2019. In the near term, many space enthusiasts excitedly await Juno's arrival at Jupiter next Monday.

APOD: 2016 April 6 - Auroras and the Magnetosphere of Jupiter
Explanation: Jupiter has auroras. Like near the Earth, the magnetic field of our Solar System's largest planet compresses when impacted by a gust of charged particles from the Sun. This magnetic compression funnels charged particles towards Jupiter's poles and down into the atmosphere. There, electrons are temporarily excited or knocked away from atmospheric gases, after which, when de-exciting or recombining with atmospheric ions, auroral light is emitted. The featured illustration portrays the magnificent magnetosphere around Jupiter in action. In the inset image released last month, the Earth-orbiting Chandra X-ray Observatory shows unexpectedly powerful X-ray light emitted by Jovian auroras, depicted in false-colored purple. That Chandra inset is superposed over an optical image taken at a different time by the Hubble Space Telescope. This aurora on Jupiter was seen in October 2011, several days after the Sun emitted a powerful Coronal Mass Ejection (CME).

APOD: 2016 March 3 - Moons and Jupiter
Explanation: Some of the Solar System's largest moons rose together on February 23. On that night, a twilight pairing of a waning gibbous Moon and Jupiter was captured in this sharp telescopic field of view. The composite of short and long exposures reveals the familiar face of our fair planet's own large natural satellite, along with a line up of the ruling gas giant's four Galilean moons. Left to right, the tiny pinpricks of light are Callisto, Io, Ganymede, [Jupiter], and Europa. Closer and brighter, our own natural satellite appears to loom large. But Callisto, Io, and Ganymede are actually larger than Earth's Moon, while water world Europa is only slightly smaller. In fact, of the Solar System's six largest planetary satellites, only Saturn's moon Titan is missing from the scene. (Editor's note: Composite corrected for orientation and field of view posted on March 7.)

APOD: 2015 October 25 - Jupiter and Venus from Earth
Explanation: It was visible around the world. The sunset conjunction of Jupiter and Venus in 2012 was visible almost no matter where you lived on Earth. Anyone on the planet with a clear western horizon at sunset could see them. Pictured above in 2012, a creative photographer traveled away from the town lights of Szubin, Poland to image a near closest approach of the two planets. The bright planets were separated only by three degrees and his daughter striking a humorous pose. A faint red sunset still glowed in the background. Jupiter and Venus will be at it again this week before sunrise, passing under two degree from each other -- and even with bonus planet Mars nearby.

APOD: 2015 July 3 - Venus and Jupiter are Far
Explanation: On June 30 Venus and Jupiter were actually far apart, but both appeared close in western skies at dusk. Near the culmination of this year's gorgeous conjunction, the two bright evening planets are captured in the same telescopic field of view in this sharp digital stack of images taken after sunset from Poznań in west-central Poland. In fact, banded gas giant Jupiter was about 910 million kilometers from Poland. That's over 11 times farther than crescent Venus, only 78 million kilometers distant at the time. But since the diameter of giant planet Jupiter is over 11 times larger than Venus both planets show about the same angular size. Of course, 16th century Polish astronomer Nicolaus Copernicus would also have enjoyed the simultaneous telescopic view including Jupiter's four Galilean moons and a crescent Venus. Observations of Jupiter's moons and Venus' crescent phase were evidence for the Copernican or heliocentric model of the solar system.

APOD: 2015 July 2 - Venus and Jupiter are Close
Explanation: On June 30, Venus and Jupiter were close in western skies at dusk. Near the culmination of this year's gorgeous conjunction, the two bright evening planets are captured in the same telescopic field of view in this image taken after sunset from Bejing, China. As the two bright planets set together in the west, a nearly Full Moon rose above the horizon to the south and east. Imaged that night with the same telescope and camera, the rising Moon from the opposite part of the sky is compared with the planetary conjunction for scale in the digitally composited image. The full lunar disk covers an angle of about 1/2 degree on the sky. Visible as well in binoculars and small telescopes are Venus' crescent and Jupiter's four Galilean moons. Of course, Venus and Jupiter are still close.

APOD: 2015 July 1 - Venus, Jupiter, and Noctilucent Clouds
Explanation: Have you seen the passing planets yet? Today the planets Jupiter and Venus pass within half a degree of each other as seen from Earth. This conjunction, visible all over the world, is quite easy to see -- just look to the west shortly after sunset. The brightest objects visible above the horizon will be Venus and Jupiter, with Venus being the brighter of the two. Featured above, the closing planets were captured two nights ago in a sunset sky graced also by high-level noctilucent clouds. In the foreground, the astrophotographer's sister takes in the vista from a bank of the Sec Reservoir in the Czech Republic. She reported this as the first time she has seen noctilucent clouds. Jupiter and Venus will appear even closer together tonight and will continue to be visible in the same part of the sky until mid-August.

APOD: 2015 May 15 - Jupiter, Ganymede, Great Red Spot
Explanation: In this sharp snapshot, the Solar System's largest moon Ganymede poses next to Jupiter, the largest planet. Captured on March 10 with a small telescope from our fair planet Earth, the scene also includes Jupiter's Great Red Spot, the Solar System's largest storm. In fact, Ganymede is about 5,260 kilometers in diameter. That beats out all three of its other fellow Galilean satellites, along with Saturn's Moon Titan at 5,150 kilometers and Earth's own Moon at 3,480 kilometers. Though its been shrinking lately, the Great Red Spot's diameter is still around 16,500 kilometers. Jupiter, the Solar System's ruling gas giant, is about 143,000 kilometers in diameter at its equator. That's nearly 10 percent the diameter of the Sun.

APOD: 2015 February 6 - Jupiter Triple-Moon Conjunction
Explanation: Our solar system's ruling giant planet Jupiter and 3 of its 4 large Galilean moons are captured in this single Hubble snapshot from January 24. Crossing in front of Jupiter's banded cloud tops Europa, Callisto, and Io are framed from lower left to upper right in a rare triple-moon conjunction. Distinguishable by colors alone icy Europa is almost white, Callisto's ancient cratered surface looks dark brown, and volcanic Io appears yellowish. The transiting moons and moon shadows can be identified by sliding your cursor over the image, or following this link. Remarkably, two small, inner Jovian moons, Amalthea and Thebe, along with their shadows, can also be found in the sharp Hubble view. The Galilean moons have diameters of 3,000 to 5,000 kilometers or so, comparable in size to Earth's moon. But odd-shaped Amalthea and Thebe are only about 260 and 100 kilometers across respectively.

APOD: 2014 August 21 - Venus and Jupiter at Dawn
Explanation: On Monday morning, Venus and Jupiter gathered close in dawn skies, for some separated by about half the width of a full moon. It was their closest conjunction since 2000, captured here above the eastern horizon before sunrise. The serene and colorful view is from Istia beach near the city of Capoliveri on the island of Elba. Distant lights and rolling hills are along Italy's Tuscan coast. Of course, the celestial pair soon wandered apart. Brighter Venus headed lower, toward the eastern horizon and the glare of the Sun, while Jupiter continues to rise a little higher now in the sky near dawn. The two brightest planets meet again next June 30th, in the evening twilight above the western horizon.

APOD: 2014 May 17 - Hubble's Jupiter and Shrinking Great Red Spot
Explanation: Gas giant Jupiter is the solar system's largest world with about 320 times the mass of planet Earth. It's also known for a giant swirling storm system, the Great Red Spot, featured in this sharp Hubble image from April 21. Nestled between Jupiter-girdling cloud bands, the Great Red Spot itself could still easily swallow Earth, but lately it has been shrinking. The most recent Hubble observations measure the spot to be about 10,250 miles (16,500 kilometers) across. That's the smallest ever measured by Hubble and particularly dramatic when compared to 14,500 miles measured by the Voyager 1 and 2 flybys in 1979, and historic telescopic observations from the 1800s indicating a width of about 25,500 miles on its long axis. Current indications are that the rate of shrinking is increasing for the long-lived Great Red Spot.

APOD: 2013 November 2 - Jupiter's Triple Shadow Transit
Explanation: This webcam and telescope image of banded gas giant Jupiter shows the transit of three shadows cast by Jupiter's moons in progress, captured in Belgian skies on October 12 at 0528 UT. Such a three shadow transit is a relatively rare event, even for a large planet with many moons. Visible in the frame are the three Galilean moons responsible, Callisto at the far left edge, Io closest to Jupiter's disk, and Europa below and just left of Io. Of their shadows on the sunlit Jovian cloud tops, Callisto casts the most elongated one near the planet's south polar region at the bottom. Io's shadow is above and right of Jupiter's Great Red Spot. Of course viewed from Jupiter's perspective, these shadow crossings could be seen as solar eclipses, analogous to the Moon's shadow crossing the sunlit face of planet Earth.

APOD: 2013 February 15 - Shadows Across Jupiter
Explanation: Two dark shadows loom across the banded and mottled cloud tops of Jupiter in this sharp telescopic view. In fact, captured on January 3rd, about a month after the ruling gas giant appeared at opposition in planet Earth's sky, the scene includes the shadow casters. Visible in remarkable detail at the left are the large Galilean moons Ganymede (top) and Io. With the two moon shadows still in transit, Jupiter's rapid rotation has almost carried its famous Great Red Spot (GRS) around the planet's limb from the right. The pale GRS was preceded by the smaller but similar hued Oval BA, dubbed Red Spot Jr., near top center. North is down in the inverted image.

APOD: 2012 November 28 - Jupiter and Io
Explanation: On December 3 (UT), Jupiter, the solar system's largest planet, will be at opposition, opposite the Sun in planet Earth's sky, shining brightly and rising as the Sun sets. That configuration results in Jupiter's almost annual closest approach to planet Earth. So, near opposition the gas giant offers earthbound telescopes stunning views of its stormy, banded atmosphere and large Galilean moons. For example, this sharp series was recorded on the night of November 16/17 from the island of Sardinia near Dolianova, Italy. North is up in the images that show off Jupiter's famous Great Red Spot, and planet girdling dark belts and light zones. Also seen in transit is Jupiter's volcanic moon Io, its round, dark shadow tracking across the Jovian cloud tops as the sequence progresses left to right.

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 July 20 - Moon Meets Jupiter
Explanation: Skygazers around planet Earth enjoyed the close encounter of planets and Moon in July 15's predawn skies. And while many saw bright Jupiter next to the slender, waning crescent, Europeans also had the opportunity to watch the ruling gas giant pass behind the lunar disk, occulted by the Moon as it slid through the night. Clouds threaten in this telescopic view from Montecassiano, Italy, but the frame still captures Jupiter after it emerged from the occultation along with all four of its large Galilean moons. The sunlit crescent is overexposed with the Moon's night side faintly illuminated by Earthshine. Lined up left to right beyond the dark lunar limb are Callisto, Ganymede, Jupiter, Io, and Europa. In fact, Callisto, Ganymede, and Io are larger than Earth's Moon, while Europa is only slightly smaller.

APOD: 2012 June 17 - Jupiter's Rings Revealed
Explanation: Why does Jupiter have rings? Jupiter's rings were discovered in 1979 by the passing Voyager 1 spacecraft, but their origin was a mystery. Data from the Galileo spacecraft that orbited Jupiter from 1995 to 2003 later confirmed that these rings were created by meteoroid impacts on small nearby moons. As a small meteoroid strikes tiny Adrastea, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit. Pictured above is an eclipse of the Sun by Jupiter, as viewed from Galileo. Small dust particles high in Jupiter's atmosphere, as well as the dust particles that compose the rings, can be seen by reflected sunlight.

APOD: 2012 April 27 - Jupiter and the Moons of Earth
Explanation: Planet Earth has many moons. Its largest artifical moon, the International Space Station, streaks through this lovely skyview with clouds in silhouette against the fading light of a sunset. Captured from Stuttgart, Germany last Sunday, the frame also includes Earth's largest natural satellite 1.5 days after its New Moon phase. Just below and left of the young crescent is Jupiter, another bright celestial beacon hovering near the western horizon in early evening skies. Only briefly, as seen from the photographer's location, Jupiter and these moons of Earth formed the remarkably close triple conjunction. Of course, Jupiter has many moons too. In fact, close inspection of the photo will reveal tiny pin pricks of light near the bright planet, large natural satellites of Jupiter known as Galilean moons.

APOD: 2012 April 8 - Io: Moon Over Jupiter
Explanation: How big is Jupiter's moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the above picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. The Cassini spacecraft itself was about 10 million kilometers from Jupiter when recording the image data.

APOD: 2012 March 18 - Jupiter and Venus from Earth
Explanation: It was visible around the world. The sunset conjunction of Jupiter and Venus was visible last week almost no matter where you lived on Earth. Anyone on the planet with a clear western horizon at sunset could see them. This week the two are still notable, even though Jupiter has sunk below the brighter Venus. And if you look higher in the sky you can see Mars as well. Pictured above, a creative photographer traveled away from the town lights of Szubin, Poland to image a near closest approach of the two planets almost a week ago. The bright planets were separated only by three degrees and his daughter striking a humorous pose. A faint red sunset still glowed in the background. Although this conjunction is drawing to a close, another conjunction between Venus and Jupiter will occur next May.

APOD: 2012 March 2 - Jupiter Unplugged
Explanation: Five hand drawn sketches of Jupiter were used to create this beautifully detailed flat map of the ruling gas giant's turbulent cloud tops. Made with colored pencils at the eyepiece of a 16 inch diameter telescope, the original drawings are about 5 inches (12.5 cm) in diameter. The drawn planisphere map dimensions are 16x8 inches (40x20 cm). Observing on different dates in November and December of 2011, astronomical artist Fred Burgeot has relied on Jupiter's rotation to cover the planet's complete circumference. Digital animator Pascal Chauvet has also translated Burgeot's drawings into an intriguing video (vimeo), synthesizing a telescopic view of the rotating planet with a tilt and phase appropriate for the observing dates. The video includes the Galilean moons moving along their orbits, beginning with Ganymede and Io casting shadows as they glide in front of Jupiter, followed by Europa and Callisto passing behind the planet's banded disk.

APOD: 2011 December 6 - Jupiter Rotation Movie from Pic du Midi
Explanation: Observe the graceful twirl of the Solar System's largest planet. Many interesting features of Jupiter's enigmatic atmosphere, including dark bands and light zones, can be followed in detail. A careful inspection will reveal that central clouds rotate slightly faster than clouds toward the poles. The famous Great Red Spot is visible at first but soon rotates out of view, only to return near the movie's end. Other smaller storm systems ocassionally appear. As large as Jupiter is, it rotates in only 10 hours. Our small Earth, by comparison, takes 24 hours to complete a spin cycle. The above high-resolution time-lapse movie was captured over the past year by the one-meter Telescope at the Pic du Midi Observatory in the French Pyrenees. Since hydrogen and helium gas are colorless, and those elements compose most of Jupiter's expansive atmosphere, what trace elements create the observed colors of Jupiter's clouds remains unknown.

APOD: 2011 October 23 - Jupiter's Clouds from New Horizons
Explanation: The New Horizons spacecraft took some stunning images of Jupiter on its way out to Pluto. Famous for its Great Red Spot, Jupiter is also known for its regular, equatorial cloud bands, visible through even modest sized telescopes. The above image, horizontally compressed, was taken in 2007 near Jupiter's terminator and shows the Jovian giant's wide diversity of cloud patterns. On the far left are clouds closest to Jupiter's South Pole. Here turbulent whirlpools and swirls are seen in a dark region, dubbed a belt, that rings the planet. Even light colored regions, called zones, show tremendous structure, complete with complex wave patterns. The energy that drives these waves surely comes from below. New Horizons is the fastest space probe ever launched, has now passed the orbits of Saturn and Uranus and is on track to reach Pluto in 2015.

APOD: 2011 October 22 - Jupiter Near Opposition
Explanation: On October 29 (UT), Jupiter, the solar system's largest planet, will be at opposition, opposite the Sun in planet Earth's sky, shining brightly and rising as the Sun sets. That configuration results in Jupiter's almost annual closest approach to planet Earth, so near opposition the gas giant offers earthbound telescopes stunning views of its stormy, banded atmosphere and large Galilean moons. This sharp snapshot of Jupiter was captured on October 13 with the 1 meter telescope at the Pic Du Midi mountain top observatory in the French Pyrenees. North is up in the image that shows off oval shaped vortices and planet girdling dark belts and light zones. Also seen in remarkable detail, Jupiter's icy Ganymede, the solar system's largest moon, is emerging from behind the planet (top) while volcanic Io enters the frame near the lower left edge.

APOD: 2011 August 9 - Juno Rockets Toward Jupiter
Explanation: Next stop: Jupiter. Last week included one of the few times in history that humanity launched something completely off the Earth, moving away so fast that it will never return. Well, almost -- Juno's planned trajectory actually brings it homeward bound in about two years, zipping by, this time using the Earth's gravity to pull it to an even higher speed, high enough to reach Jupiter. The above video depicts the launch of Juno aboard a Atlas V rocket. When the robotic Juno spacecraft reaches Jupiter in 2016, it will spend just over a year circling the Solar System's largest planet, using its unique cadre of instruments to probe the planet, sending back clues of its structure and origin. Then Juno will be instructed to dive into the thick atmosphere of the Jovian giant, taking as much data as it can before it melts.

APOD: 2011 May 2 - Jupiter's Great Red Spot from Voyager 1
Explanation: It is a hurricane twice the size of the Earth. It has been raging at least as long as telescopes could see it, and shows no signs of slowing. It is Jupiter's Great Red Spot, the largest swirling storm system in the Solar System. Like most astronomical phenomena, the Great Red Spot was neither predicted nor immediately understood after its discovery. Still today, details of how and why the Great Red Spot changes its shape, size, and color remain mysterious. A better understanding of the weather on Jupiter may help contribute to the better understanding of weather here on Earth. The above image is a recently completed digital enhancement of an image of Jupiter taken in 1979 by the Voyager 1 spacecraft as it zoomed by the Solar System's largest planet. At about 117 AU from Earth, Voyager 1 is currently the most distant human made object in the universe and expected to leave the entire solar heliosheath any time now.

APOD: 2011 March 18 - Mercury and Jupiter at Sunset
Explanation: When warm sunset hues begin to fade, two celestial beacons now shine in the evening twilight, Mercury and Jupiter. Wandering away from the Sun in planet Earth's sky, Mercury will offer good views this month as spring approaches in the northern hemisphere where the ecliptic plane makes a steep angle with the western horizon. But Jupiter will continue sinking lower in the sky after sunset. In fact, the normally elusive Mercury shines well above Jupiter and the orange sunset glow in this serene sky. Captured earlier this week from the island of of Frösön in northern Sweden, the scene looks across Lake Storsjön toward the village of Hallen and distant mountains. Of course, even better views of Mercury can be had by the MESSENGER spacecraft, now orbiting the Solar System's innermost planet!

APOD: 2010 November 29 - Dark Belt Reappearing on Jupiter
Explanation: Why are planet-circling clouds disappearing and reappearing on Jupiter? Although the ultimate cause remains unknown, planetary meteorologists are beginning to better understand what is happening. Earlier this year, unexpectedly, Jupiter's dark Southern Equatorial Belt (SEB) disappeared. The changes were first noted by amateurs dedicated to watching Jupiter full time. The South Equatorial Band has been seen to change colors before, although the change has never been recorded in such detail. Detailed professional observations revealed that high-flying light-colored ammonia-based clouds formed over the planet-circling dark belt. Now those light clouds are dissipating, again unveiling the lower dark clouds. Pictured above two weeks ago, far infrared images -- depicted in false-color red -- show a powerful storm system active above the returning dark belt. Continued observations of Jupiter's current cloud opera, and our understanding of it, is sure to continue.

APOD: 2010 June 3 - Jupiter from the Stratosphere
Explanation: SOFIA, the Stratospheric Observatory for Infrared Astronomy, captured its "first light" images on May 26, from an altitude of 35,000 feet. While flying above most of planet Earth's infrared-absorbing water vapor, SOFIA's premier infrared views of the cosmos included this remarkable false-color image (right panel) of Jupiter. For comparison, on the left is a recent, ground-based visible light image. Both show our solar system's ruling gas giant without its dark southern equatorial belt (normally seen in the upper hemisphere in this orientation). That familiar feature faded from view early in May. But the bright white stripe in SOFIA's image is a region of Jupiter's clouds transparent to infrared light, offering a glimpse below the cloud tops.

APOD: 2010 January 24 - Watch Jupiter Rotate
Explanation: What would it be like to coast by Jupiter and watch it rotate? This was just the experience of the New Horizons spacecraft as it approached and flew by Jupiter in 2007. Clicking on the image will bring up a movie of what the robotic spacecraft saw. Visible above in the extensive atmosphere of the Solar System's largest planet are bands and belts of light and dark clouds, as well as giant rotating storm systems seen as ovals. Other movies compiled by New Horizons and other passing spacecraft have captured the clouds swirling and moving relative to themselves. Jupiter has a diameter of about eleven times that of our Earth, and rotates once in about 10 hours. The robotic New Horizons spacecraft, launched four years ago last week, continues to speed toward the outer Solar System and has recently passed the halfway point between Earth and Pluto. New Horizons will reach Pluto in 2015.

APOD: 2009 September 8 - Unexpected Impact on Jupiter
Explanation: Two months ago, something unexpected hit Jupiter. First discovered by an amateur astronomer Anthony Wesley on 2009 July 19, the impact was quickly confirmed and even imaged by the Hubble Space Telescope during the next week. Many of the world's telescopes then zoomed in on our Solar System's largest planet to see the result. Some of these images have been complied into the above animation. Over the course of the last month and a half, the above time-lapse sequence shows the dark spot -- first created when Jupiter was struck -- deforming and dissipating as Jupiter's clouds churned and Jupiter rotated. It is now thought that a small comet -- perhaps less than one kilometer across -- impacted Jupiter on or before 2009 July 19. Although initially expected to be visible for only a week, astronomers continue to track atmospheric remnants of the impact for new information about winds and currents in Jupiter's thick atmosphere.

APOD: 2009 September 7 - Jupiter Over the Mediterranean
Explanation: This vacation included a sight to remember. Pictured above, a picturesque starscape capped a serene seascape as seen from Turkey this past August. In the above digitally stitched panorama, the Gelidonya Lighthouse shines in the foreground before a calm Mediterranean Sea. On the left, Jupiter is the brightest point in the image and since on the same side of the Sun as the Earth, was near its yearly brightest. Glowing just shy of magnitude -3, Jupiter was brighter than any star in the sky, and brighter even than Mars was during its famously bright opposition of 2003 August. On the right, the band of the Milky Way Galaxy fades into distant atmospheric haze above the horizon. Jupiter is nearing the closest part of its elliptical orbit to the Sun and so will appear even brighter during its next opposition in 2010 September.

APOD: 2009 July 31 - Hubble View: Jupiter Impact
Explanation: This sprawling dark marking is Jupiter's latest impact scar, a debris plume created as a small asteroid or comet disintegrated after plunging into the gas giant's atmosphere. Located in Jupiter's south polar region, the new feature was discovered by Australian amateur astronomer Anthony Wesley on July 19. On July 23rd Wesley's discovery was followed up by the Hubble Space Telescope with its newly installed Wide Field Camera 3, creating this sharpest view of the evolving debris plume. Estimates indicate that the impacting object itself was several hundred meters across. Similar impact markings were created when pieces of Comet Shoemaker-Levy 9 slammed into Jupiter's cloud bands in July of 1994.

APOD: 2009 July 23 - Jupiter's Impact Scar
Explanation: In July of 1994 pieces of Comet Shoemaker-Levy 9 collided with planet Jupiter. The explosive impacts sent plumes of debris high into the Jovian atmosphere creating dark markings or scars, visible for a time against the cloud bands. Remarkably, 15 years later, another impact scar was discovered in the Jovian atmosphere by amateur astronomer Anthony Wesley as he examined images of the gas giant taken from his home observatory just outside Murrumbateman NSW Australia. Jupiter's south pole is at the top in this July 19 discovery image, with Jupiter rotating from right to left. The dark marking, also likely caused by a comet or asteroid impact, is near the top of the view, left of a pre-existing, whitish, oval-shaped storm. NASA's Infrared Telescope Facility images from Mauna Kea, Hawaii later confirmed the likely impact site's dark scar and plume of particles in Jupiter's upper atmosphere. Since 2006, major discovery observations by amateur astronomers have also included two red spots on Jupiter.

APOD: 2009 July 14 - Moons and Jupiter
Explanation: Earth's Moon and planet Jupiter made a beautiful pairing in the night sky late last week. This skyscape recorded on July 11 from Brittany in north western France captures the bright conjunction through a cloud bank. The clouds add drama and mystery to the scene but they were also positioned to reduce the intense moonlight. As a result, the exposure captures Jupiter's own Galilean moons (lower right) as tiny pinpricks of light, lined up and hugging both sides of the solar system's ruling gas giant. Later this week, the Moon is headed for a conjunction with Mars and Venus in the dawn sky.

APOD: 2009 January 6 - Jupiter Eclipsing Ganymede
Explanation: How hazy is Jupiter's upper atmosphere? To help find out, astronomers deployed the Hubble Space Telescope to watch Jupiter eclipse its moon Ganymede. Although Ganymede circles Jupiter once a week, a particularly useful occultation occurs more rarely. Such an occultation was captured in great visual detail in April 2007. When near Jupiter's limb, Ganymede reflects sunlight though Jupiter's upper atmosphere, allowing astronomers to search for haze by noting a slight dimming at different colors. One result of this investigation was the above spectacular image, where bands of clouds that circle Jupiter are clearly visible, as well as magnificent swirling storm systems such as the Great Red Spot. Ganymede, at the image bottom, also shows noticeable detail on its dark icy surface. Since Jupiter and Ganymede are so bright, many eclipses can be seen right here on Earth with a small telescope.

APOD: 2008 July 18 - Jupiter over Ephesus
Explanation: A brilliant Jupiter shares the sky with the Full Moon tonight. Since Jupiter is near opposition, literally opposite the Sun in planet Earth's sky, Jupiter will rise near sunset just like the Full Moon. Of course, opposition is also the point of closest approach, with Jupiter shining at its brightest and offering the best views for skygazers. Recorded late last month, this moving skyscape features Jupiter above the southeastern horizon and the marbled streets of the ancient port city of Ephesus, located in modern day Turkey. At the left is a temple dedicated to the Roman emperor Hadrian. The beautiful night sky also includes the arc of the northern summer Milky Way. Lights on the horizon are from the nearby town of Selçuk. Clicking on the image will download the scene as a panorama.

APOD: 2008 May 23 - Jupiter's Three Red Spots
Explanation: For about 300 years Jupiter's banded atmosphere has shown a remarkable feature to telescopic viewers, a large swirling storm system known as The Great Red Spot. In 2006, another red storm system appeared, actually seen to form as smaller whitish oval-shaped storms merged and then developed the curious reddish hue. Now, Jupiter has a third red spot, again produced from a smaller whitish storm. All three are seen in this image made from data recorded on May 9 and 10 with the Hubble Space Telescope's Wide Field and Planetary Camera 2. The spots extend above the surrounding clouds and their red color may be due to deeper material dredged up by the storms and exposed to ultraviolet light, but the exact chemical process is still unknown. For scale, the Great Red Spot has almost twice the diameter of planet Earth, making both new spots less than one Earth-diameter across. The newest red spot is on the far left (west), along the same band of clouds as the Great Red Spot and is drifting toward it. If the motion continues, the new spot will encounter the much larger storm system in August. Jupiter's recent outbreak of red spots is likely related to large scale climate change as the gas giant planet is getting warmer near the equator.

APOD: 2008 February 2 - Venus and Jupiter in Morning Skies
Explanation: These two celestial beacons shining brightly in the east before sunrise are actually children of the Sun, the planets Venus and Jupiter. The second and third brightest objects in the sky at Night after the Moon, Venus and Jupiter appeared separated by about 2 degrees when this picture was taken on January 30th, but closed to within nearly half a degree early yesterday morning. In the serene foreground is the shoreline along the Miankaleh Peninsula and Gorgan Bay, an important bird and wildlife refuge in the southeastern Caspian Sea. Over the next two days, early morning risers around the globe will be able to enjoy a close pairing of Venus and Jupiter with an old crescent Moon.

APOD: 2008 January 8 - A Jupiter-Io Montage from New Horizons
Explanation: As the New Horizons spacecraft sweeps through the Solar System, it is taking breathtaking images of the planets. In February of last year, New Horizons passed Jupiter and the ever-active Jovian moon Io. In this montage, Jupiter was captured in three bands of infrared light making the Great Red Spot look white. Complex hurricane-like ovals, swirls, and planet-ringing bands are visible in Jupiter's complex atmosphere. Io is digitally superposed in natural color. Fortuitously, a plume was emanating from Io's volcano Tvashtar. Frost and sulfuric lava cover the volcanic moon, while red-glowing lava is visible beneath the blue sunlight-scattering plume. The robotic New Horizons spacecraft is on track to arrive at Pluto in 2015.

APOD: 2008 January 6 - Jupiter's Rings Revealed
Explanation: Why does Jupiter have rings? Jupiter's rings were discovered in 1979 by the passing Voyager 1 spacecraft, but their origin was a mystery. Data from the Galileo spacecraft that orbited Jupiter from 1995 to 2003 later confirmed that these rings were created by meteoroid impacts on small nearby moons. As a small meteoroid strikes tiny Adrastea, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit. Pictured above is an eclipse of the Sun by Jupiter, as viewed from Galileo. Small dust particles high in Jupiter's atmosphere, as well as the dust particles that compose the rings, can be seen by reflected sunlight.

APOD: 2007 October 15 - Jupiter's Clouds from New Horizons
Explanation: The New Horizons spacecraft took some stunning images of Jupiter earlier this year while on the way out to Pluto. Famous for its Great Red Spot, Jupiter is also known for its regular, equatorial cloud bands, visible through even modest sized telescopes. The above image was taken near Jupiter's terminator, and shows that the Jovian giant possibly has the widest diversity of cloud patterns in our Solar System. On the far left are clouds closest to Jupiter's south pole. Here turbulent whirlpools and swirls are seen in a dark region, dubbed a belt, that rings the planet. Even light colored regions, called zones, show tremendous structure, complete with complex wave patterns. The energy that drives these waves likely comes from below. New Horizons is the fastest space probe ever launched, and is zipping through the Solar System on track to reach Pluto in 2015.

APOD: 2007 May 25 - Jupiter, Vesta, and the Milky Way
Explanation: In this gorgeous skyscape, gas giant Jupiter along with the stars and cosmic dust clouds of the Milky Way hang over the southern horizon in the early morning hours as seen from Stagecoach, Colorado, USA. Recorded on Thursday, Jupiter is the brightest object near picture center. Along with the stunning Milky Way, Jupiter is hard to miss, but a careful inspection of the view also reveals main belt asteroid Vesta. Of all the asteroids Vesta is the brightest and is now just bright enough to be visible to the naked eye from locations with very dark, clear skies. Vesta (as well as Jupiter) appears relatively bright now because it is near opposition, literally opposite the Sun in planet Earth's sky and closest to Earth in its orbit. For Vesta, this opposition offers the best viewing in many years. The year 2007 also coincides with the 200th anniversary of the asteroid's discovery. Starting late next month, NASA plans to launch the Dawn mission intended to explore Vesta (and Ceres) and the main asteroid belt.

APOD: 2007 March 29 - Jupiter Moon Movie
Explanation: South is toward the top in this frame from a stunning movie featuring Jupiter and moons recorded last Thursday from the Central Coast of New South Wales, Australia. In fact, three jovian moons and two red spots are ultimately seen in the full video as they glide around the solar system's ruling gas giant. In the early frame above, Ganymede, the largest moon in the solar system, is off the lower right limb of the planet, while intriguing Europa is visible against Jupiter's cloud tops, also near the lower right. Jupiter's new red spot junior is just above the broad white band in the planet's southern (upper) hemisphere. In later frames, as planet and moons rotate (right to left), red spot junior moves behind Jupiter's left edge while the Great Red Spot itself comes into view from the right. Also finally erupting into view at the right, is Jupiter's volcanic moon, Io. To download the full 2 megabyte movie as an animated gif file, click on the picture.

APOD: 2007 March 12 - Watch Jupiter Rotate
Explanation: What would it be like to coast by Jupiter and watch it rotate? This was just the experience of the New Horizons spacecraft as it approached and flew by Jupiter earlier this year. Clicking on the image will bring up a movie of what the robotic spacecraft saw. Visible above in the extensive atmosphere of the Solar System's largest planet are bands and belts of light and dark clouds, as well as giant rotating storm systems seen as ovals. Other movies compiled by New Horizons and other passing spacecraft have captured the clouds swirling and moving relative to themselves. Jupiter has a diameter of about eleven times that of our Earth, and rotates once in about 10 hours. The robotic New Horizons spacecraft continues to speed toward the outer Solar System where it is expected to approach Pluto in 2015.

APOD: 2007 March 7 - New Horizons Spacecraft Passes Jupiter
Explanation: A new spacecraft is headed for the outer Solar System. Named New Horizons, this robotic explorer passed Jupiter last week after being launched only in early 2006. New Horizons is being pulled by Jupiter's gravity to a greater speed toward its next target: Pluto in 2015. During its encounter with Jupiter, New Horizons was able to capture new images of many Jovian moons, Jupiter's complex and ever-changing atmosphere, and Jupiter's Little Red Spot, pictured above. Formed over the past few years from several smaller storms, Jupiter's Little Red Spot survived a near miss with Jupiter's better-known Great Red Spot last year. The above image of Jupiter covers over twice the diameter of the Earth.

APOD: 2006 May 5 - Jupiter and the Red Spots
Explanation: Jupiter's Great Red Spot is a swirling storm seen for over 300 years, since the beginning of telescopic observations. But in February 2006, planetary imager Christopher Go noticed it had been joined by Red Spot Jr - formed as smaller whitish oval-shaped storms merged and then developed the remarkable reddish hue. This sharp Hubble Space Telescope image showing the two salmon-colored Jovian storms was recorded in April. About half the size of the original Red Spot, Red Spot Jr. is similar in diameter to planet Earth. Seen here below and left of the ancient storm system, it trails the Great Red Spot by about an hour as the planet rotates from left to right. While astronomers still don't exactly understand why Jupiter's red spots are red, they do think the appearance of Red Spot Jr. provides evidence for climate change on the Solar System's ruling gas giant.

APOD: 2005 January 9 - Jupiter's Rings Revealed
Explanation: Why does Jupiter have rings? Jupiter's rings were discovered in 1979 by the passing Voyager 1 spacecraft, but their origin was a mystery. Data from the Galileo spacecraft that orbited Jupiter from 1995 to 2003 later confirmed that these rings were created by meteoroid impacts on small nearby moons. As a small meteoroid strikes tiny Adrastea, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit. Pictured above is an eclipse of the Sun by Jupiter, as viewed from Galileo. Small dust particles high in Jupiter's atmosphere, as well as the dust particles that compose the rings, can be seen by reflected sunlight.

APOD: 2004 December 9 - Jupiter and the Moon's Shadowed Horizon
Explanation: Early Tuesday morning, December 7th, June Croft thought the southeastern sky above Atmore, Alabama, USA was beautiful. Watching the Moon rise through gossamer clouds, she noted, " ... the crescent Moon looked like it was held in the sky by a star just off its shadowed horizon." What was that star? Bright Jupiter of course, and some watched as the Moon actually occulted or passed in front of the Solar System's reigning gas giant planet. For astronomer Jimmy Westlake in Colorado, Jupiter was already hidden at moonrise that morning, but later he was able to record this lovely image, not unlike the view that inspired Croft. Seen through gossamer clouds, Jupiter along with large Jovian satellites Ganymede and Callisto (bottom to top) has emerged from behind the crescent Moon's shadowed horizon.

APOD: 2004 November 8 - Jupiter and Venus at Sunrise
Explanation: What are those bright objects in the morning sky? Early morning dog walkers, among many others across our world's Northern Hemisphere, have likely noticed tremendously bright Venus hanging in the eastern sky just before sunrise. Looking a bit like an approaching airplane, Venus holds its place in the sky and never seems to land. Last week, impressive but less bright Jupiter appeared within a degree of the Venusian orb, creating a dazzling sky that you might appreciate a bit more than your dog. This night sky early show will change slightly over the next week, with the planets moving past each other, Mars moving into the picture, guest stars like Spica appearing to shift in the background, and even a crescent Moon stopping in for a cameo. Pictured above last week, Jupiter and Venus were photographed rising before the Sun over the city of Bursa, Turkey.

APOD: 2003 December 4 - New Horizons at Jupiter
Explanation: Headed for the first close-up exploration of the Pluto-Charon system and the icy denizens of the Kuiper belt, NASA's New Horizons spacecraft is pictured here in an artist's vision of the robot probe outward bound. The dramatic scene depicts the 465 kilogram spacecraft about one year after a planned 2006 launch, following a flyby of gas giant Jupiter. While the Jupiter flyby will be used as a gravity assist maneuver to save fuel and cut travel time to the outer reaches of the Solar System, it will also provide an opportunity to test instruments and study the giant planet, its moons, and magnetic fields. The Sun is seen from eight hundred million kilometers away, with inner planets Earth, Venus, and Mercury aligned on the left. A dim crescent of outermost Galilean moon Callisto, orbiting Jupiter just inside of the spacecraft's trajectory, appears to the upper right of the fading Sun. Left of Jupiter itself is Europa and in the distant background are the faint, unresolved stars and dust clouds of the Milky Way. New Horizons' planned arrival at Pluto-Charon is in the summer of 2015.

APOD: 2003 November 14 - Jupiter Portrait
Explanation: Every day is a cloudy day on Jupiter, the Solar System's reigning gas giant. And swirling cloud tops are all you see in this stunningly detailed true color image, a portion of a large digital mosaic portrait of Jupiter recorded from the Cassini spacecraft during its Jovian flyby in December 2000. The smallest features visible are about 60 kilometers across. Jupiter's composition is dominated by hydrogen and the clouds contain hydrogen compounds like ammonia, hydrogen sulfide, and even water. A truly giant planet, Jupiter's diameter is over 11 times the diameter of Earth and the smallest storms visible in the Cassini Jupiter portrait are similar in size to large terrestrial hurricanes. Now traveling beyond Jupiter, the Cassini spacecraft is scheduled to reach the Saturnian system in July of 2004.

APOD: 2003 October 9 - Radio Jupiter
Explanation: This view of gas giant Jupiter, made from data recorded at the Very Large Array radio observatory near Socorro, New Mexico, may not look too familiar. In fact, there is no sign of a bright, round planet striped with cloud bands, sporting a Great Red Spot. Instead, the radio waves mapped in this false-color image are produced by energetic electrons trapped within Jupiter's intense magnetic field. The radio emitting region extends far beyond Jupiter's cloud tops, to over twice the visible radius of the planet, and surrounds Jupiter like an oversized version of Earth's Van Allen radiation belt. While it glows strongly at radio wavelengths, Jupiter's radiation belt is invisible in the more familiar optical and infrared views which show the Jovian cloud tops and atmospheric features in reflected sunlight.

APOD: 2003 September 6 - Jupiter Unpeeled
Explanation: Slice Jupiter from pole to pole, peel back its outer layers of clouds, stretch them onto a flat surface ... and for all your trouble you'd end up with something that looks a lot like this. Scrolling right will reveal the full picture, a color mosaic of Jupiter from the Cassini spacecraft. The mosaic is actually a single frame from a fourteen frame movie constructed from image data recorded by Cassini during its leisurely flyby of the solar system's largest planet in late 2000. The engaging movie approximates Jupiter's cloud motions over 24 jovian rotations. To make it, a series of observations covering Jupiter's complete circumference 60 degrees north and south of the equator were combined in an animated cylindrical projection map of the planet. As in the familiar rectangular-shaped wall maps of the Earth's surface, the relative sizes and shapes of features are correct near the equator but become progressively more distorted approaching the polar regions. In the Cassini movie, which also features guest appearances by moons Io and Europa, the smallest cloud structures visible at the equator are about 600 kilometers across.

APOD: 2003 April 3 - Jupiter in the Hive
Explanation: If you can find planet Jupiter in tonight's sky, then you can also find M44, popularly known as the Beehive star cluster. In fact, with a pair of binoculars most casual skygazers should find it easy to zero in on this celestial scene. It should be easy because after sunset Jupiter presently rules the night as the brightest "star" overhead. Now near the stationary part of its wandering path through the heavens, Jupiter will obligingly linger for a while at a spot only a degree or so southeast of M44 in the relatively faint constellation Cancer. Seen here in a photograph from March 28, Jupiter (lower left) is strongly overexposed with the stars of M44 swarming above and to the right. The picture approximately corresponds to the view when looking through a typical pair of binoculars. Jupiter is about 30 light-minutes from our fair planet while M44, one of the closest star clusters, is around 600 light-years away.

APOD: 2003 March 19 - Jupiter's Great Dark Spot
Explanation: Seventeenth century astronomer Giovanni Domenico Cassini was an astute observer of Jupiter's Great Red Spot. So it seems only fitting that his namesake, the Cassini spacecraft, has enabled detailed observations of another planet-sized blemish -- Jupiter's Great Dark Spot. Unlike the Red Spot, the Great Dark Spot lies near Jupiter's north pole and seems to appear and disappear over periods of months rather than persisting for hundreds of years. Seen at ultraviolet wavelengths, the dark feature resides in the Jovian stratosphere confined by pole-encircling winds, analogous to planet Earth's antarctic ozone hole. This image of the Dark Spot is a single frame from a movie created with data recorded during the spacecraft's year 2000 flyby of Jupiter. Projected to show Jupiter's north polar region, no data are available for the blank central area, while the Great Dark Spot lies above and just left of center. The white circle marks 60 degrees latitude and the blue contour outlines a persistent Jovian auroral zone which may be related to the formation of the Great Dark Spot.

APOD: 2003 March 13 - WIRO at Jupiter
Explanation: Gazing out over the mountaintops from the Wyoming InfraRed Observatory (WIRO), astronomers recently recorded this bizarre looking image of the solar system's ruling planet, gas giant Jupiter. The false-color picture is a composite of images taken to test a sophisticated digital camera operating at liquid helium temperatures and sensitive to wavelengths about three times longer than visible red light. At those infrared wavelengths (near 2.1 microns) the molecular hydrogen and methane gas in Jupiter's dense lower atmosphere strongly absorb sunlight, so the normally bright, banded planet looks very dark. But particles and haze over the equator and poles rise above the absorbing layers into Jupiter's stratosphere and reflect the infrared sunlight. Also clearly extending into the Jovian stratosphere is the famous Great Red Spot seen here in yellow just under the equatorial band at the right. North is up in this view and Jupiter's rapid 10 hour rotation will soon carry the Great Red Spot behind the planet's right limb.

APOD: 2003 March 9 - Farewell Jupiter
Explanation: Next stop: Saturn. The Cassini spacecraft, launched from Earth in 1997, has now swung past Jupiter and should arrive at Saturn in the year 2004. Pictured to the left is a parting shot from Cassini in 2001 January that would not have been possible from Earth: Jupiter showing a crescent phase. From the Earth and all points sunward of Jupiter, the gas giant will always appear more fully lit than a crescent. Recent analysis of Jupiter images taken from Cassini bolsters indications that clouds well up from below in the dark colored belts, not the light colored zones, as believed previously. After arriving at Saturn, Cassini will decelerate to orbit the ringed world and send a probe to its enigmatic moon Titan.

APOD: 2002 December 7 - Jupiter, Io, and Shadow
Explanation: Pictured above is the innermost of Jupiter's Galilean satellites, Io, superposed in front of the gas giant planet. To the left of Io is a dark spot that is Io's own shadow. A solar eclipse would be seen from within the shadow spot on Jupiter. Viewed from planet Earth, similar shadows of Jupiter's large moons can often be seen crossing the giant planet's disk. But during the next several months, the Galilean moons can also be seen crossing in front of each other as, for a while, their orbits lie nearly edge-on when viewed by earthbound observers. This true-color contrast-enhanced image was taken two years ago by the robot spacecraft Cassini, as it passed Jupiter on its way to Saturn in 2004.

APOD: 2002 September 25 - Jupiter, Moons, and Bees
Explanation: Rising before the Sun on September 4, Jupiter and an old cresent Moon gathered in the dim constellation of Cancer. Watching from a hillside near Austin, Texas, planet Earth, astrophotographer Russell Croman recorded this view of their passing as clouds gracefully dimmed the brilliant moonlight. Earthshine illuminates the lunar night side and on close inspection, bright Jupiter at the lower right appears tightly flanked by its own four large Galilean moons. Next to Jupiter lies a loose swarm of stars just below the clouds. The stars are the brighter members of the nearby star cluster M44, popularly known as the Beehive cluster. Croman's remarkable digital image has been processed only slightly to improve the visibility of the earthshine region and Jupiter's moons.

APOD: 2002 July 6 - Io: Moon Over Jupiter
Explanation: How big is the Jovian moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts it nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. The Cassini spacecraft itself was about 10 million kilometers from Jupiter when recording the image data.

APOD: 2002 June 25 - Venus and Jupiter Over Belfast
Explanation: Venus and Jupiter appeared to glide right past each other earlier this month. In a slow day-by-day march, Jupiter sank into the sunset horizon while Venus remained high and bright. The conjunction ended the five-planet party visible over the last two months. Jupiter, of course, is much further away from the Earth and Sun than Venus, so the passing was really just an angular illusion. Pictured above on June 3, a fading sunset finds Venus shining over Jupiter above clouds, mountains, and the city lights of Belfast, Northern Ireland.

APOD: 2002 June 16 - Jupiter's Rings Revealed
Explanation: Why does Jupiter have rings? Jupiter's rings were discovered in 1979 by the passing Voyager 1 spacecraft, but their origin was a mystery. Data from the Galileo spacecraft currently orbiting Jupiter later confirmed that these rings were created by meteoroid impacts on small nearby moons. As a small meteoroid strikes tiny Adrastea, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit. Pictured above is an eclipse of the Sun by Jupiter, as viewed from Galileo. Small dust particles high in Jupiter's atmosphere, as well as the dust particles that compose the rings, can be seen by reflected sunlight.

APOD: 2002 March 1 - Jupiter's Great X Ray Spot
Explanation: The Solar System's largest planet, gas giant Jupiter, is famous for its swirling Great Red Spot. In the right hand panel above, the familiar giant planet with storm system and cloud bands is shown in an optical image from the passing Cassini spacecraft. In the left hand panel, a false-color image from the orbiting Chandra Observatory presents a corresponding x-ray view of Jupiter. The Chandra image shows clearly, for the first time, x-ray spots and auroral x-ray emission from the poles. The x-ray spot dominating the emission from Jupiter's north pole (top) is perhaps as surprising for astronomers today as the Great Red Spot once was. Confounding previous theories, the x-ray spot is too far north to be associated with heavy electrically charged particles from the vicinity of volcanic moon Io. Chandra data also show that the spot's x-ray emission mysteriously pulsates over a period of about 45 minutes.

APOD: 2002 February 5 - Giant Storm Systems Battle on Jupiter
Explanation: Two of the largest storm systems on Jupiter are colliding, and nobody is sure what will result. The larger storm is the famous Great Red Spot, while the smaller is a large white oval. Both are swirling cloud systems that circulate on Jupiter. The white oval is part of a belt of clouds that circles Jupiter faster than the Great Red Spot. The oval started being slowed by the Great Red Spot two weeks ago and the collision could last another month. The oval will likely survive but could possibly be disrupted or absorbed. The two storm systems went at it at least once before in 1975 causing the Spot's red color to fade for several years. The passing Voyager 2 robot spacecraft took the above picture of Jupiter's Great Red Spot in 1979. A different white oval was then visible below the Spot.

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 August 8 - Farewell Jupiter
Explanation: Next stop: Saturn. The Cassini spacecraft, launched from Earth four years ago, has now swung past Jupiter and should arrive at Saturn in the year 2004. Pictured to the left is a parting shot from Cassini in January that would not have been possible from Earth: Jupiter showing a crescent phase. From the Earth and all points sunward of Jupiter, the gas giant will always appear more fully lit than a crescent. After arriving at Saturn, Cassini will decelerate to orbit the ringed world and send a probe to its enigmatic moon Titan.

APOD: 2001 April 20 - Io: Moon Over Jupiter
Explanation: How big is the Jovian moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts it nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. The Cassini spacecraft itself was about 10 million kilometers from Jupiter when recording the image data.

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: 2001 February 15 - Jupiter Unpeeled
Explanation: Slice Jupiter from pole to pole, peel back its outer layers of clouds, stretch them onto a flat surface ... and for all your trouble you'd end up with something that looks a lot like this. Scrolling right will reveal the full picture, a color mosaic of Jupiter from the Cassini spacecraft. The mosaic is actually a single frame from a fourteen frame movie constructed from image data recorded by Cassini during its leisurely flyby of the solar system's largest planet late last year. The engaging movie approximates Jupiter's cloud motions over 24 jovian rotations. To make it, a series of observations covering Jupiter's complete circumference 60 degrees north and south of the equator were combined in an animated cylindrical projection map of the planet. As in the familiar rectangular-shaped wall maps of the Earth's surface, the relative sizes and shapes of features are correct near the equator but become progressively more distorted approaching the polar regions. In the Cassini movie, which also features guest appearances by moons Io and Europa, the smallest cloud structures visible at the equator are about 600 kilometers across. (Note: Downloading a large gif or quicktime version of the movie may take 15 minutes or longer.)

APOD: 2001 February 1 - Jupiter's Brain
Explanation: Gas giant Jupiter is the solar system's largest world with about 320 times the mass of planet Earth. Famous for its Great Red Spot, Jupiter is also known for its regular, equatorial cloud bands, visible in very modest sized telescopes. The dark belts and light-colored zones of Jupiter's cloud bands are organized by planet girdling winds which reach speeds of up to 500 kilometers per hour. On toward the Jovian poles though, the cloud structures become more mottled and convoluted until, as in this Cassini spacecraft mosaic of Jupiter, the planet's polar region begins to look something like a brain! This striking equator-to-pole change in cloud patterns is not presently understood but may be due in part to the effect of Jupiter's rapid rotation or to convection vortices generated at high latitudes by the massive planet's internal heat loss. The Cassini spacecraft recorded this dramatically detailed view of Jupiter during its turn of the millennium flyby enroute to Saturn.

APOD: 2001 January 2 - Jupiter, Europa, and Callisto
Explanation: As the robot Cassini spacecraft rounds Jupiter on its way toward Saturn, it has taken a sequence of images of the gas giant with its four largest moons. Previously released images have highlighted Ganymede and Io. Pictured above are the two remaining Galilean satellites: Europa and Callisto. Europa is the bright moon superposed near Jupiter's Great Red Spot, while Callisto is the dark moon near the frame edge. Callisto is so dark that it would be hard to see here if its brightness was not digitally enhanced. Recent evidence indicates that both moons hold salt-water seas under surface ice that might be home to extra-terrestrial life. By noting the times that moons disappeared and reappeared behind Jupiter in 1676, Ole Roemer was able to make the first accurate estimation of the speed of light.

APOD: 2000 December 26 - Jupiter, Io, and Shadow
Explanation: Just as planets orbit our Sun, Jupiter's Moons orbit Jupiter. Pictured above is the closest of Jupiter's Galilean Satellites, Io, superposed in front of the giant planet it circles. To the left of Io is a dark spot that is its own shadow. The tremendous complexities that can be seen in Jupiter's banded, swirling atmosphere are being studied and may provide insight as to how Earth's atmosphere behaves. The above true-color contrast-enhanced image was taken two weeks ago by the robot spacecraft Cassini, currently passing Jupiter and on its way to Saturn in 2004. Engineers continue to study the Cassini spacecraft itself to understand why it required more force than normal to turn one of its maneuvering wheels.

APOD: 2000 December 19 - A Close Up of Aurora on Jupiter
Explanation: Jupiter has aurorae. Like Earth, the magnetic field of the gas giant funnels charged particles released from the Sun onto the poles. As these particles strike the atmosphere, electrons are temporarily knocked away from existing gas molecules. Electric force attracts these electrons back. As the electrons recombine to remake neutral molecules, auroral light is emitted. In the above recently released photograph by the Hubble Space Telescope taken in ultraviolet light, the aurorae appear as annular sheets around the pole. Unlike Earth's aurorae, Jupiter's aurorae include several bright streaks and dots. These marks are caused by magnetic flux tubes connecting Jupiter to its largest moons. Specifically, Io caused the bright streak on the far left, Ganymede caused the bright dot below center, and Europa caused the dot to its right.

APOD: 2000 December 18 - Oceans Under Jupiter's Ganymede
Explanation: The search for extraterrestrial life came back into our own Solar System last week with the announcement that there may be liquid oceans under the surface of Jupiter's moon Ganymede. Ganymede now joins Callisto and Europa as moons of Jupiter that may harbor seas of liquid water under layers of surface ice. The ocean hypothesis surfaced as an explanation for Ganymede's unusually strong magnetic field. Ganymede, the largest moon in the Solar System, also has the largest measured magnetic field of any moon. Some exobiologists hypothesize that life may be able to emerge in such an ocean, much as it did in the oceans of ancient Earth. Above, a frame from a computer simulation shows what it would look like to fly over the surface of Ganymede, as extrapolated from photographs of the grooved moon taken by the robot spacecraft Galileo currently orbiting Jupiter.

APOD: 2000 December 12 - Jupiter Eyes Ganymede
Explanation: Who keeps an eye on the largest moon in the Solar System? This moon, visible on the lower right, is Ganymede, and the planet it orbits, Jupiter, seems to be keeping a watchful eye, as its Great Red Spot appears serendipitously nearby. This recently released enhanced-contrast image from the robot spacecraft Cassini captures new details of the incredible intricacies of Jupiter's complex cloud patterns. Features as small as 250 kilometers can be seen. Counter-clockwise rotating high-pressure white ovals that are similar to the Great Red Spot appear in the red band below the spot. Between these spots are darker low-pressure systems that rotate clockwise. The hydrogen and helium that compose most of Jupiter's clouds is nearly invisible - the trace chemicals that give Jupiter these colors remain unknown. The Cassini spacecraft is using Jupiter to pull it toward Saturn, where it is scheduled to arrive in 2004.

APOD: 2000 November 23 - Cassini At Jupiter: Red Spot Movie
Explanation: Everything is big on Jupiter, the solar system's reigning gas giant. For example, Jupiter's Great Red Spot is a hurricane-like storm system at least twice the diameter of planet Earth. Approaching Jupiter in early October the Cassini spacecraft recorded the images used in this excellent movie of the swirling storm system and planet-circling cloud bands. Seven mosaicked frames make up the movie sequence, each separated by one or two rotation periods (Jupiter rotates about once every 10 hours). The sequence is viewed as a simple cylindrical map projection spanning 50 degrees north to 50 degrees south of the Jovian equator. Can you see the small bright "clouds" which seem to suddenly appear west (left) of the Red Spot? Data from the Galileo spacecraft, orbiting Jupiter since 1996, suggest that these features are large lightning storms. Saturn-bound, the Cassini spacecraft will take a few months to fly by Jupiter, coordinating Jovian explorations with Galileo and picking up speed for the final leg of its interplanetary journey.

APOD: 2000 November 18 - Jupiter And Family
Explanation: This composite image features classic portraits of members of one of the Solar System's most prominent families - Jupiter and its four large "Galilean" moons. Starting from the top the moons are Io, Europa, Ganymede, and Callisto. The top-to-bottom order is also the order of increasing distance from Jupiter. These are big moons indeed which attend the largest planet. The smallest of the lot, Europa, is the size of Earth's moon while Ganymede is the largest moon in the Solar System. In fact, Ganymede with a diameter of 3,100 miles, is larger than the planets Mercury and Pluto. The swirling Great Red Spot appears at the edge of Jupiter. A hurricane-like storm system that has persisted for over 300 years, two to three earths could fit inside it. Battered Callisto's image was recorded during the 1979 flyby of Voyager. The other portraits were taken by the Galileo spacecraft which began exploring the Jovian system in 1995.

APOD: 2000 November 5 - Jupiter Swallows Comet Shoemaker Levy 9
Explanation: What happens when a comet encounters a planet? If the planet has a rocky surface, a huge impact feature will form. A giant planet like Jupiter, however, is mostly gas. When Comet Shoemaker-Levy 9 struck Jupiter in 1994, each piece was swallowed into the vast Jovian atmosphere. Pictured above is a time-lapse sequence of the result of two fragments striking Jupiter. As the comet plunged in, it created large dark marks that gradually faded. The high temperature of gas under Jupiter's cloud tops surely caused the comet fragment to melt before it plunged very far. Because Jupiter is much more massive than any comet, the orbit of Jupiter around the Sun did not change noticeably.

APOD: 2000 October 11 - Cassini Spacecraft Approaches Jupiter
Explanation: A new spacecraft has entered the outer Solar System: Cassini. Launched in 1997 and bound for Saturn in 2004, Cassini sent back the above image last week while approaching the giant planet Jupiter. Cassini joins the Galileo spacecraft currently in orbit around Jupiter in studying the gas giant and its moons. In fact, observations involving both spacecraft simultaneously are planned in the coming months. This color picture was taken when Cassini was 81.3 million kilometers from Jupiter. The alternating dark and bright bands characteristic of Jupiter's cloud tops can be easily seen. Jupiter's moon Europa is also seen at the far right of the image casting a round shadow on the planet.

APOD: 2000 September 26 - Approaching Jupiter
Explanation: In 1979 the Voyager 1 spacecraft compiled this view as it approached the gas giant Jupiter. Snapping a picture every time the Great Red Spot was properly aligned, the above time-lapse sequence shows not only spot rotation but also the swirling of neighboring clouds. Since Jupiter takes about 10 hours to rotate, this short sequence actually covers several days. Voyager 1 shot past Jupiter rapidly taking pictures on which many discoveries would be made, including previously unknown cloud patterns, rings, moons, and active volcanoes on Jupiter's moon Io. Voyager is moving so fast that it will one day leave our Solar System.

APOD: 2000 June 6 - A Continuous Eruption on Jupiter's Moon Io
Explanation: A volcano on Jupiter's moon Io has been photographed recently during an ongoing eruption. Hot glowing lava is visible on the left on this representative-color image. A glowing landscape of plateaus and valleys covered in sulfur and silicate rock surrounds the active volcano. Many features including several of the dark spots have evolved between February 2000, when the robot spacecraft Galileo currently orbiting Jupiter took this picture, and November 1999. Io is slightly larger than Earth's Moon and is the closest large moon to Jupiter. The above image shows a region about 250 kilometers across. How the internal structure of Io creates these active volcanoes remains under investigation.

APOD: July 18, 1999 - Jupiter from Voyager
Explanation: This picture of the planet Jupiter was taken by the Voyager 1 spacecraft as it passed the planet in 1979. Jupiter, a gas giant planet with no solid surface, is the largest planet in the Solar System and is made mostly of the hydrogen and helium. Clearly visible in the above photo is the Great Red Spot, a giant, hurricane-like storm system that rotates with the clouds of Jupiter. It is so large three complete Earths could fit inside it. Astronomers have recorded this giant storm on Jupiter for over 300 years.

APOD: March 8, 1999 - A Jupiter Venus Conjunction
Explanation: Venus and Jupiter appeared unusually close together in the sky last month. The conjunction was easily visible to the unaided eye because Venus appears brighter than any background star. The two planets were not significantly closer in space - Venus just passed nearly in front of Jupiter as seen from the Earth. Visible in the above photograph are actually five planets. The faint dot near the top is Saturn. Venus is the brightest spot near the center, and Jupiter is just above it. Perhaps the hardest to see is Mercury, visible below Venus but above the foreground Earth. A single line nearly connects all the planets, a result of all planets orbiting the Sun in a single plane called the ecliptic.

APOD: January 5, 1999 - A New Jupiter Oval Rotates
Explanation: Even Jupiter can do the twist. Large cloud systems on Jupiter rotate, and the newly formed oval pictured above is no different. This new oval formed earlier this year from the collision of two smaller ovals: an occurrence not unlike two large storms merging into one huge hurricane. Even this new swirling storm, however, is small compared to Jupiter's Great Red Spot. The above-animated frame dithers between two pictures of the new oval taken roughly an hour apart. The Galileo spacecraft currently orbiting the giant Jovian planet captured the pictures.

APOD: October 22, 1998 - Jupiter: When Storms Collide
Explanation: Sometime in February, two of three long-lived Jovian storm systems known as "white ovals" apparently collided and merged -- forming what is now likely the second largest storm in the Solar System, after the famous Great Red Spot. The whitish, oval-shaped storms in Jupiter's banded atmosphere have been telescopically studied since the 1930s, but details of this surprising merger are unknown as Jupiter and Earth were on opposite sides of the Sun when it happened. The aftermath is shown in the (top panel) Hubble Space Telescope picture, taken in July as part of the evidence investigators are using to reconstruct the facts of the case. Centered are the swirling white clouds of the newly created storm system which is about as wide as planet Earth. At its left is the remaining smaller white oval which seems to be drifting away from the larger new storm. Atmospheric temperature data from the Galileo spacecraft represented in the (bottom panel) false-color image show the new storm as a dark feature, cooler than its surroundings.

APOD: August 4, 1998 - Jupiter Swallows Comet Shoemaker Levy 9
Explanation: What happens when a comet encounters a planet? If the planet has a rocky surface, a huge impact feature will form. A giant planet like Jupiter, however, is mostly gas. When Comet Shoemaker-Levy 9 struck Jupiter in 1994, each piece was swallowed into the vast Jovian atmosphere. Pictured above is a time-lapse sequence of the result of two fragments striking Jupiter. As the comet plunged in, it created large dark marks that gradually faded. The high temperature of gas under Jupiter's cloud tops surely caused the comet fragment to melt before it plunged very far. Because Jupiter is much more massive than any comet, the orbit of Jupiter around the Sun did not change noticeably.

APOD: July 28, 1998 - Impact on Jupiter
Explanation: In 1993, a strange string of comet pieces was discovered near the planet Jupiter. So unusual a sight, Comet Shoemaker-Levy 9 (SL9) quickly became the object of much scientific curiosity. Studies showed that the Sun would soon perturb the orbit of SL9 so that it would actually strike Jupiter in July 1994. The studies were right. The above picture shows the impact site of SL9's fragment G on Jupiter's cloud-tops. The size of the dark outer ring is roughly the size of the Earth. Since Jupiter is mostly gas, the comet melted and evaporated before plunging too far into Jupiter's atmosphere.

APOD: February 2, 1998 - A Triple Eclipse on Jupiter
Explanation: Part of Jupiter is missing. Actually, three parts appear to be missing. In reality though, the three dark spots seen in the above photograph are only shadows. The unusual alignment of three of Jupiter's moons between the Jovian giant and the Sun was imaged last November 10th. The shadows of Io, Callisto, and Ganymede move across Jupiter as these moons progress in their orbits. It was by noting the times of eclipse of Jupiter's moons in 1675 that Ole Roemer became the first person to measure the speed of light. When a shadow from Earth's Moon crosses the Earth's surface, the people inside the shadow see an eclipse of the Sun.

APOD: December 16, 1997 - Night Lightning on Jupiter
Explanation: Why is there lightning on Jupiter? Lightning is a sudden rush of electrically charged particles from one location to another. To create lightning, charges must first separate inside a cloud. On Earth, drafts of colliding ice and water droplets usually create this charge separation, but what happens on Jupiter? Many astronomers theorize that Jovian lightning is also created in clouds containing water ice. To help investigate this, the above photograph was taken in October by the Galileo spacecraft now orbiting Jupiter. Clouds are dimly lit by sunlight reflected off Jupiter's moon Io. The bright flashes appear to originate in active regions at the level where water clouds would exist, and illuminate an even lower cloud level containing ammonia. One thing is for sure: lightning on Jupiter is a lot brighter than lighting on Earth.

APOD: November 27, 1997 - Jupiter's Inner Moons
Explanation: The potato-shaped inner moons of Jupiter are lined-up in this mosaic "family portrait" of these tiny Jovian satellites. The individual images were recorded over the last year by NASA's Galileo spacecraft and are scaled to the moons' relative sizes. Left to right in increasing order of distance from Jupiter are Metis (longest dimension 37 miles), Adrastea (12 miles), Amalthea (154 miles), and Thebe (72 miles). All these moons orbit in the zone between Io and Jupiter's rings, are bombarded by high-energy ions within the Jovian magnetosphere, and are probably locked in synchronous rotation by Jupiter's strong gravity. Why are they shaped like potatoes? Like the asteroids and the diminutive moons of Mars, their own gravity is not strong enough to mold them into spheres.

APOD: November 21, 1997 - Jupiter: Moon, Ring, and Clouds
Explanation: An inner moon, an edge-on, planet-girdling ring, and high altitude cloud bands are visible in this mosaic of infrared images of gas giant Jupiter. The moon Metis, 25 miles wide and about 80,000 miles from the planet, is the bright spot at the upper right. Metis lies within Jupiter's faint, tenuous ring, and may be a source of ring material. Recorded on September 17th by the NICMOS instrument on board the Hubble Space Telescope, these pictures also emphasize atmospheric features high above the main jovian cloud deck. Methane gas in Jupiter's atmosphere absorbs the near infrared light causing deeper clouds to appear dark at these wavelengths. Clouds riding above most of the atmospheric methane are bright. The circular dark spot just above the brightest cloud band is an image artifact.

APOD: September 29, 1997 - Jupiter And Family
Explanation: This composite image features classic portraits of members of one of the Solar System's most prominent families - Jupiter and its four large "Galilean" moons. Starting from the top the moons are Io, Europa, Ganymede, and Callisto. The top-to-bottom order is also the order of increasing distance from Jupiter. These are big moons indeed which attend the largest planet. The smallest of the lot, Europa, is the size of Earth's moon while Ganymede is the largest moon in the Solar System. In fact, Ganymede with a diameter of 3,100 miles, is larger than the planets Mercury and Pluto. The swirling Great Red Spot appears at the edge of Jupiter. A hurricane-like storm system that has persisted for over 300 years, two to three earths could fit inside it. Battered Callisto's image was recorded during the 1979 flyby of Voyager. The other portraits were taken by the Galileo spacecraft which began exploring the Jovian system in 1995.

APOD: September 20, 1997 - The Clouds of Jupiter
Explanation: What makes the colors in Jupiter's clouds? With a mean temperature of 120 degrees Kelvin (-153 degrees Celsius) and a composition dominated by hydrogen (about 90%), and helium (about 10%) with a smattering of hydrogen compounds like methane and ammonia, the blue, orange, and brown cloud bands and the salmon colored "red" spot are hard to explain. Trouble is -- at the cool cloud temperatures Jupiter's atmospheric constituents should be colorless! Some suggest that more colorful hydrogen compounds well up from warmer regions in the atmosphere, tinting the cloud tops. Alternatively, compounds of trace elements like sulfur may color the clouds. Jupiter's colors do indicate the clouds' altitudes, blue is lowest through red as highest. The dark colored bands are called belts and the light colored ones zones. In addition to the belts and zones, the Voyager missions revealed the presence of intricate vortices visible, for example, in this 1979 image from the Voyager I flyby. Centuries of visual observations of Jupiter have revealed that the colors of its clouds are ever changing.

APOD: August 8, 1997 - White Oval Clouds on Jupiter
Explanation: What are those white ovals all over Jupiter? Storms! Jupiter's clouds can swirl rapidly in raised high-pressure storm systems that circle the planet. The above pictured white ovals are located near the Great Red Spot, and have persisted on Jupiter since the 1930s. The Great Red Spot has persisted for at least 300 years. Currently, no one knows why ovals last as long as they do. White ovals are confined to circular belts around Jupiter, but can interact to cause nearby chaotic cloud regions.

APOD: August 7, 1997 - Jupiter's Ring Halo
Explanation: Why do small particles hover around Jupiter's rings? These particles form a previously unknown ring halo, recently discovered by the robot spacecraft Galileo currently orbiting Jupiter. Galileo obtained this image when on the far side of Jupiter - from this orientation scattered sunlight makes the halo ring visible. The amount of scattering indicates that halo particles are very small - perhaps 100 times smaller than the width of a human hair. Particles this small are believed to survive only for years, and so must somehow be replenished to Jupiter's ancient ring system. One possible explanation for this unusual halo is that electromagnetic fields around Jupiter gently push small charged particles out of the ring plane. This false color image has been artificially stretched in the vertical direction to highlight the ring halo.

APOD: June 12, 1997 - Jupiter's Dry Spots
Explanation: Known for its spectacular images of Jupiter's moons, Io, Ganymede, Callisto, and Europa, the robot spacecraft Galileo has also aggressively explored the Jovian atmosphere. In December of 1995, Galileo's atmospheric probe descended into Jupiter's clouds and reported a surprising absence of water. It is now believed that the probe entered through one of Jupiter's dry spots, similar to the dark region in this image of the swirling Jovian cloud deck. The smallest features visible here are tens of miles in size. These dry regions appear to correspond to locations where winds converge creating downdrafts. The downdrafts generate local cloudless clearings through which Jupiter's deeper warmer layers can be glimpsed. Just as the dark areas are extremely dry, the surroundings are full of moisture. The contrast is analogous to the desert and tropics of Earth.

APOD: June 9, 1997 - An Auroral Ring on Jupiter
Explanation: Do other planets have aurora? Terrestrial and spacecraft observations have found evidence for aurora on Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. In the above false-color photograph, a good portion of an auroral ring was captured recently in optical light by the Galileo spacecraft in orbit around Jupiter. Auroral rings encircle a planet's magnetic pole, and result from charged particles spiraling down magnetic field lines. Although the surroundings near Jupiter are much different than Earth, the auroral rings appear similar.

APOD: May 12, 1997 - Lightning on Jupiter
Explanation: Does lightning occur only on Earth? Spacecraft in our Solar System have detected radio signals consistent with lightning on other planets, including Venus, Jupiter, Saturn, Uranus, and Neptune. In the above photograph, optical flashes from Jupiter were photographed recently by the Galileo orbiter. Each of the circled dots indicates lightning. The numbers label lines of latitude. The size of the largest spot is about 500 kilometers across and might be high clouds illuminated by several bright lightning strokes.

APOD: March 31, 1997 - NGC 3242: The 'Ghost of Jupiter' Planetary Nebula
Explanation: It's a weed, it's Jupiter, no it's - actually planetary nebula NGC 3242. After a star like our Sun completes fusion in its core, it throws off its outer layers it a striking display called a planetary nebula. NGC 3242 is such a planetary nebula, with the stellar remnant white dwarf star visible at the center. This nebula is sometimes called "The Ghost of Jupiter" for its similar appearance to the familiar planet. NGC 3242 is much farther away however, than the measly 40 light-minutes distance to Jupiter. In fact, by comparing the apparent expansion rate with the actual rate determined from Doppler studies, astronomers have estimated the distance to NGC 3242 to be about 1400 light-years away. The red FLIERs visible near the edges of the nebula remain mysterious.

APOD: February 5, 1997 - Running Red Rings Around Jupiter
Explanation: Jupiter has rings, too. Unlike Saturn's bright rings which are composed of chunks of ice, Jupiter's rings are darker and appear to consist of fine particles of rock. The six pictures above were taken in infrared light from the Infrared Telescope Facility in Hawaii in 1994, and cover a time span of two hours. Quite visible are Jupiter's rings, bands and spots in the outer atmosphere. Also visible in the photos, however, are two small Jovian moons. Metis, only 40 kilometers across, appears in the second picture as a dim spot on the rings to the right of Jupiter. Amalthea, much larger and brighter, appears in the third frame on the far left, and can be seen to pass across the face of Jupiter in frames four and five. The origin of Jupiter's rings remains unknown, although hypothesized to be created by material scattered from meteorite impacts onto Jupiter's moons.

APOD: January 9, 1997 - Hazing Jupiter
Explanation: A dramatic mosaic of recent images from the Galileo spacecraft reveals details of swirling clouds and a thick stratospheric haze in the atmosphere of Jupiter, the Solar System's largest planet. This false color representation is keyed to altitude - red indicates cloud features near the top of the gas giant's extensive atmosphere while blue corresponds to features at depth. North is up in the mosaic, centered at about 50 degrees northern Jovian latitude, and the limb or edge of the planet arcs across the upper right. The line of sight looking toward the limb emphasizes the high altitude, red haze. What causes the red haze? It may well be created as energetic electrons and other charged particles swept up by Jupiter's magnetosphere are funneled along magnetic field lines and bombard the atmosphere near the polar regions. Charged magnetospheric particles can also create Aurora.

APOD: November 27, 1996 - Storm Clouds Over Jupiter
Explanation: Storm clouds, similar to the familiar cumulonimbus thunderheads of Earth, appear to be present on Jupiter. The mosaic of images above shows the region near the raging edge of Jupiter's Great Red Spot, itself some 2 to 3 Earths wide, as observed by the Galileo spacecraft in June of this year. The false colors represent altitude. Low altitude clouds are blue, high, thick clouds are white and high, thin clouds are pink, with the box at the upper right containing the high cloud features likened to the storm clouds of Earth. Scientists speculate that these features are evidence for an abundance of water in at least some regions of Jupiter's atmosphere. On Earth, atmospheric water vapor plays an important role in driving winds - this could well be true on Jupiter, where winds reach up to 300 miles per hour.

APOD: October 18, 1996 - Jupiter's Auroras
Explanation: Auroras are especially large on Jupiter. In pictures released yesterday, the Hubble Space Telescope imaged these unusual light displays in more detail than ever before. Jupiter's auroras are linked to its volcanic moon Io. Io's volcanoes release particles, some of which become ionized, trapped by Jupiter's magnetic field, and rain down on the gas giant. The resulting auroral displays may be thousands of times brighter than any auroral display on Earth, and involve unusual spots. The above pictures show how the extended auroral emissions rotate with Jupiter, while the auroral spots stay synchronized to Io as it circles Jupiter.

APOD: August 27, 1996 - Galileo Zooms in on Jupiter's Red Spot
Explanation: What does the largest storm system ever recorded look like close-up? This storm system is Jupiter's Great Red Spot and it was captured recently in detail by the robot spacecraft Galileo now in orbit around Jupiter. Using real images from three color filters, the Galileo team was able to compute what a person would see if able to float just above this ancient rotating cloud system. But don't get too close - remember that Jupiter's Great Red Spot is a cold, high pressure area more than twice as wide as planet Earth.

APOD: August 3, 1996 - Jupiter's Colorful Clouds
Explanation: What makes the colors in Jupiter's clouds? With a mean temperature of 120 degrees Kelvin (-153 degrees Celsius) and a composition dominated by Hydrogen (about 90%), and Helium (about 10%) with a smattering of hydrogen compounds like methane and ammonia, astronomers have been hard pressed to explain the blue, orange and brown cloud bands and the salmon colored "red" spot. Trouble is -- at the cool cloud temperatures Jupiter's atmospheric constituents should be colorless! Some suggest that more colorful hydrogen compounds well up from warmer regions in the atmosphere, tinting the cloud tops. Alternatively, compounds of trace elements like sulfur may color the clouds. The colors do indicate the clouds' altitudes, blue is lowest through red as highest. The dark colored bands are called belts and the light colored ones zones. In addition to the belts and zones, the Voyager missions revealed the presence of intricate vortices visible, for example, in this 1979 image from the Voyager I flyby. Centuries of visual observations of Jupiter have revealed that the colors of its clouds are ever changing.

APOD: January 23, 1996 - Beneath Jupiter's Clouds
Explanation: This near-infrared image of Jupiter was made using instrumentation at NASA's Infrared Telescope Facility, located on the summit of Mauna Kea, Hawaii, in support of the Galileo mission to Jupiter. The brightest spots indicated by the false red shading are relatively clear areas and represent glimpses beneath the outer layer of Jupiter's obscuring cloud tops. On December 7, 1995 a probe from the Galileo spacecraft parachuted through these clouds for 57 minutes before melting, all the while providing the first direct sampling of the conditions there. In a recent press release of the probe's findings scientists announced some surprising results. Discoveries based on probe data included a new radiation belt 31,000 miles above the cloud tops, relatively constant high velocity winds (up to 330 mph), no obvious water clouds, low abundances of Helium and Neon, lightning occurring only 1/10th as much as on Earth, and unexpectedly high temperatures. The Galileo orbiter continues its two-year mission to explore the Jovian system.

APOD: December 7, 1995 - Galileo's Jupiter Probe
Explanation: Today, at about 5:00 pm EST, this 750 pound probe from NASA's robot spacecraft Galileo will plummet into Jupiter becoming the first probe to fly through the atmosphere of a gas giant planet. Released by the Galileo orbiter in July of this year, it has been coasting toward its rendezvous with the Solar System's largest planet. The probe will smack Jupiter's atmosphere at over 100,000 mph slowing to less than 1,000 mph in a matter of minutes, experiencing a deceleration of about 230 times the Earth's surface gravity. If all goes well, it will then deploy a parachute and descend, using sophisticated instruments to profile Jupiter's dense outer layers of hydrogen and helium gas. Pictured here before launch, the probe descent module (top)is suspended above its deceleration module aeroshell (bottom) prior to being joined. The aeroshell should protect the descent module from the initial shock and heat of entry, which will initially create an intense fireball, over twice as hot as the surface of the Sun.

APOD: December 6, 1995 - 24 Hours from Jupiter
Explanation: NASA's robot spacecraft Galileo began its long voyage to Jupiter more than six years and 2.3 billion miles ago. About 24 hours from now it will reach its destination. On arrival (December 7th, 1995), Galileo should become the first spacecraft to orbit around a gas giant planet and the first to drop a probe into a giant planet's dense atmosphere. In the above Hubble Space Telescope image, the predicted probe entry location is indicated by the arrow. If all goes well, the atmospheric probe will relay information about temperature, pressure, and composition for about an hour as it descends through Jupiter's clouds, while the orbiter will spend at least two years exploring the Jovian system. Along with advancing our knowledge of Jupiter and its environs, Galileo data is expected to reveal some of the secrets of the formation and evolution of the Solar System.

APOD: October 13, 1995 - Jupiter, Io, and Ganymede's Shadow
Explanation: Jupiter, the solar system's largest planet, is seen here next to Io, its closest Galilean moon. On the cloud tops of Jupiter near the left edge of the picture can be seen a dark circular spot which is caused by the shadow of Jupiter's largest moon Ganymede. Jupiter's cloud tops show light bands and dark belts. The clouds are primarily composed of hydrogen and helium, but their intense colors are probably caused by very small amounts of heavier elements such as sulfur or organic (carbon-containing) compounds.

APOD: August 2, 1995 - Jupiter's Rings
Explanation: Astronomers using NASA's Voyager spacecraft to search for a ring system around Jupiter discovered these faint rings in 1979. Unlike Saturn's bright rings which are composed of chunks of rock and ice, Jupiter's rings appear to consist of fine particles of dust. One possibility is that the dust is produced by impacts with Jupiter's inner moons. This false color image has been computer enhanced.

APOD: July 14, 1995 - Comet Impacts on Jupiter
Explanation: In July of 1994, pieces of Comet Shoemaker-Levy 9, also known as the "string of pearls" comet, collided with the planet Jupiter. As the comet fragments smashed in to Jupiter, the resulting explosions scattered large quantities of dusty cometary debris into the Jovian atmosphere. The clouds of debris created the multiple dark smudges visible in this picture. Jupiter's rotation causes the successive impact sites to be strung out along the cloud bands while the strong winds cause the appearance of the smudges to change with time. Jupiter's famous red spot is also visible to the left of center.

APOD: June 25, 1995 - Jupiter from Voyager
Explanation: Imagine a hurricane that lasted for 300 years! This picture of the planet Jupiter was taken by the Voyager 1 spacecraft as it passed the planet in 1979. Jupiter, a gas giant planet with no solid surface, is the largest planet in the solar system and is made mostly of the hydrogen and helium. Clearly visible in the photo is the Great Red Spot, a giant, hurricane-like storm system that rotates with the clouds of Jupiter. It is so large three complete Earths could fit inside it. Astronomers have observed this giant storm on Jupiter for over 300 years.