Astronomy Picture of the Day Search Results for "Epimetheus OR Janus"

APOD: 2022 January 4 - Moons Beyond Rings at Saturn
Explanation: What's happened to that moon of Saturn? Nothing -- Saturn's moon Rhea is just partly hidden behind Saturn's rings. In 2010, the robotic Cassini spacecraft then orbiting Saturn took this narrow-angle view looking across the Solar System's most famous rings. Rings visible in the foreground include the thin F ring on the outside and the much wider A and B rings just interior to it. Although it seems to be hovering over the rings, Saturn's moon Janus is actually far behind them. Janus is one of Saturn's smaller moons and measures only about 180 kilometers across. Farther out from the camera is the heavily cratered Rhea, a much larger moon measuring 1,500 kilometers across. The top of Rhea is visible only through gaps in the rings. After more than a decade of exploration and discovery, the Cassini spacecraft ran low on fuel in 2017 and was directed to enter Saturn's atmosphere, where it surely melted.

APOD: 2020 August 8 - Crescent Saturn
Explanation: From Earth, Saturn never shows a crescent phase. But when viewed from a spacecraft the majestic giant planet can show just a sunlit slice. This image of crescent Saturn in natural color was taken by the robotic Cassini spacecraft in 2007. It captures Saturn's rings from the side of the ring plane opposite the Sun -- the unilluminated side -- another vista not visible from Earth. Visible are subtle colors of cloud bands, the complex shadows of the rings on the planet, and the shadow of the planet on the rings. The moons Mimas, at 2 o'clock, and Janus 4 o'clock, can be seen as specks of light, but the real challenge is to find Pandora (8 o'clock). From Earth, Saturn's disk is nearly full now and opposite the Sun. Along with bright fellow giant planet Jupiter it rises in the early evening.

APOD: 2019 October 17 - Moons of Saturn
Explanation: On July 29, 2011 the Cassini spacecraft's narrow-angle camera took this snapshot and captured 5 of Saturn's moons, from just above the ringplane. Left to right are small moons Janus and Pandora respectively 179 and 81 kilometers across, shiny 504 kilometer diameter Enceladus, and Mimas, 396 kilometers across, seen just next to Rhea. Cut off by the right edge of the frame, Rhea is Saturn's second largest moon at 1,528 kilometers across. So how many moons does Saturn have? Twenty new found outer satellites bring its total to 82 known moons, and since Jupiter's moon total stands at 79, Saturn is the Solar System's new moon king. The newly announced Saturnian satellites are all very small, 5 kilometers or so in diameter, and most are in retrograde orbits inclined to Saturn's ringplane. You can help name Saturn's new moons, but you should understand the rules. Hint: A knowledge of Norse, Inuit, and Gallic mythology will help.

APOD: 2019 July 7 - Crescent Saturn
Explanation: Saturn never shows a crescent phase -- from Earth. But when viewed from beyond, the majestic giant planet can show an unfamiliar diminutive sliver. This image of crescent Saturn in natural color was taken by the robotic Cassini spacecraft in 2007. The featured image captures Saturn's majestic rings from the side of the ring plane opposite the Sun -- the unilluminated side -- another vista not visible from Earth. Pictured are many of Saturn's photogenic wonders, including the subtle colors of cloud bands, the complex shadows of the rings on the planet, and the shadow of the planet on the rings. A careful eye will find the moons Mimas (2 o'clock) and Janus (4 o'clock), but the real challenge is to find Pandora (8 o'clock). Saturn is now nearly opposite from the Sun in the Earth's sky and so can be seen in the evening starting just after sunset for the rest of the night.

APOD: 2018 May 10 - Galaxies in the River
Explanation: Large galaxies grow by eating small ones. Even our own galaxy practices galactic cannibalism, absorbing small galaxies that get too close and are captured by the Milky Way's gravity. In fact, the practice is common in the universe and illustrated by this striking pair of interacting galaxies from the banks of the southern constellation Eridanus, The River. Located over 50 million light years away, the large, distorted spiral NGC 1532 is seen locked in a gravitational struggle with dwarf galaxy NGC 1531 (right of center), a struggle the smaller galaxy will eventually lose. Seen edge-on, spiral NGC 1532 spans about 100,000 light-years. Nicely detailed in this sharp image, the NGC 1532/1531 pair is thought to be similar to the well-studied system of face-on spiral and small companion known as M51.

APOD: 2017 June 18 - Views from Cassini at Saturn
Explanation: What has the Cassini orbiter seen at Saturn? The featured music video shows some of the early highlights. In the first time-lapse sequence (00:07), a vertical line appears that is really Saturn's thin rings seen nearly edge-on. Soon some of Saturn's moon shoot past. The next sequence (00:11) features Saturn's unusually wavy F-ring that is constrained by the two shepherd moons that are also continually perturbing it. Soon much of Saturn's extensive ring system flashes by, sometimes juxtaposed to the grandeur of the immense planet itself. Cloud patterns on Titan (00:39) and Saturn (00:41) are highlighted. Clips from flybys of several of Saturn's moon are then shown, including Phoebe, Mimas, Epimetheus, and Iapetus. In other sequences, moons of Saturn appear to pass each other as they orbit Saturn. Background star fields seen by Cassini are sometimes intruded upon by bright passing moons. The robotic Cassini spacecraft has been revolutionizing humanity's knowledge of Saturn and its moons since 2004. In September, Cassini's mission will be brought to a dramatic conclusion as the spacecraft will be directed to dive into ringed giant.

APOD: 2014 November 2 - Titan Beyond the Rings
Explanation: When orbiting Saturn, be sure to watch for breathtaking superpositions of moons and rings. One such picturesque vista was visible recently to the robot Cassini spacecraft now orbiting Saturn. In 2006 April, Cassini captured Saturn's A and F rings stretching in front of cloud-shrouded Titan. Near the rings and appearing just above Titan was Epimetheus, a moon which orbits just outside the F ring. The dark space in the A ring is called the Encke Gap, although several thin knotted ringlets and even the small moon Pan orbit there.

APOD: 2012 May 21 - A Close Pass of Saturn's Moon Dione
Explanation: What's that past Dione? When making its closest pass yet of Saturn's moon Dione late last year, the robotic Cassini spacecraft snapped this far-ranging picture featuring Dione, Saturn's rings, and the two small moons Epimetheus and Prometheus. The above image captures part of the heavily cratered snow-white surface of the 1,100 kilometer wide Dione, the thinness of Saturn's rings, and the comparative darkness of the smaller moon Epimetheus. The image was taken when Cassini was only about 100,000 kilometers from the large icy moon. Future events in Cassini's continuing exploration of Saturn and its moons include tomorrow's flyby of Titan and imaging the distant Earth passing behind Saturn in June.

APOD: 2011 June 13 - Views from Cassini at Saturn
Explanation: What has the Cassini orbiter seen since arriving at Saturn? The above music video shows some of the highlights. In the first time-lapse sequence (00:07), a vertical line appears that is really Saturn's thin rings seen nearly edge-on. Soon some of Saturn's moon shoot past. The next sequence (00:11) features Saturn's unusually wavy F-ring that is constrained by the two shepherd moons that are also continually perturbing it. Soon much of Saturn's extensive ring system flashes by, sometimes juxtaposed to the grandeur of the immense planet itself. Cloud patterns on Titan (00:39) and Saturn (00:41) are highlighted. Clips from flyby's of several of Saturn's moon are then shown, including Phoebe, Mimas, Epimetheus, and Iapetus. In other sequences, moons of Saturn appear to pass each other as they orbit Saturn. Background star fields seen by Cassini are sometimes intruded upon by bright passing moons. The robotic Cassini spacecraft has been revolutionizing humanity's knowledge of Saturn and its moons since 2004.

APOD: 2010 July 12 - Moons Beyond the Rings of Saturn
Explanation: What's happened to that moon of Saturn? Nothing -- Saturn's moon Rhea is just partly hidden behind Saturn's rings. In April, the robotic Cassini spacecraft now orbiting Saturn took this narrow-angle view looking across the Solar System's most famous rings. Rings visible in the foreground include the thin F ring on the outside and the much wider A and B rings just interior to it. Although it seems to be hovering over the rings, Saturn's moon Janus is actually far behind them. Janus is one of Saturn's smaller moons and measures only about 180 kilometers across. Farther out from the camera is the heavily cratered Rhea, a much larger moon measuring 1,500 kilometers across. The top of Rhea is visible only through gaps in the rings. The Cassini mission around Saturn has been extended to 2017 to better study the complex planetary system as its season changes from equinox to solstice.

APOD: 2010 May 31 - Moons and Rings Before Saturn
Explanation: While cruising around Saturn, be on the lookout for picturesque juxtapositions of moons and rings. Another striking alignment occurred last March in the view of humanity's Saturn-orbiting Cassini spacecraft. Rhea, one of Saturn's larger moons, was caught passing Epimetheus, one of Saturn's smaller moons. Epimetheus, as pictured above, is actually well behind the heavily cratered Rhea. Further back, several of the complex rings of Saturn can be seen crossing the image horizontally. Behind both the moons and rings is giant Saturn itself, showing expansive but featureless clouds in the green light where the above image was taken. The Cassini mission around Saturn has now been extended to 2017 to better study the complex planetary system as its season changes from equinox to solstice.

APOD: 2009 May 5 - Titan Beyond the Rings
Explanation: When orbiting Saturn, be sure to watch for breathtaking superpositions of moons and rings. One such picturesque vista was visible recently to the robot Cassini spacecraft now orbiting Saturn. In 2006 April, Cassini captured Saturn's A and F rings stretching in front of cloud-shrouded Titan. Near the rings and appearing just above Titan was Epimetheus, a moon which orbits just outside the F ring. The dark space in the A ring is called the Encke Gap, although several thin knotted ringlets and even the small moon Pan orbit there. Cassini and curious Earthlings await the coming Saturnian equinox this summer when the ring plane will point directly at the Sun. Mysterious spokes and telling shadows are expected to become visible that might give away more clues about the nature of Saturn's ring particles.

APOD: 2008 May 5 - A Persistent Electrical Storm on Saturn
Explanation: How do large storms evolve on Saturn? On Earth, a hurricane can persist for weeks, while the Great Red Spot on Jupiter has been in existence for over 150 years. On Saturn, a storm system has now set a new endurance record, now being discernable for greater than three months. Electrical signals were detected from the storm in late November of 2007, while the above image was taken in early March 2008. The storm has roughly the width of planet Earth. Planetary scientists hypothesize that the storm runs deep into Saturn's cloud tops. The above image is shown in exaggerated colors combining violet and green light with light normally too red for humans to see. Visible on the upper right are shadows of Saturn's expansive ring system. Careful inspection will reveal Saturn's small moon Janus just below a ring shadow. Understanding weather on other planets helps atmospheric scientists better understand our Earth's weather. Observers of our Solar System's huge ringed world will be tracking the storm to see how it evolves and how long it will ultimately last.

APOD: 2008 February 11 - Saturn's Moon Epimetheus from the Cassini Spacecraft
Explanation: How did Epimetheus form? No one is yet sure. To help answer that question, this small moon has recently been imaged again in great detail by the robot spacecraft Cassini now orbiting Saturn. Epimetheus sometimes orbits Saturn in front of Janus, another small satellite, but sometimes behind. The above image, taken last December, shows a surface covered with craters indicating great age. Epimetheus spans about 115 kilometers across. Epimetheus does not have enough surface gravity to restructure itself into a sphere. The flattened face of Epimetheus shown above might have been created by a single large impact.

APOD: 2007 October 23 - Crescent Saturn
Explanation: Saturn never shows a crescent phase -- from Earth. But when viewed from beyond, the majestic giant planet can show an unfamiliar diminutive sliver. This image of crescent Saturn in natural color was taken by the robotic Cassini spacecraft in May. The image captures Saturn's majestic rings from the side of the ring plane opposite the Sun -- the unilluminated side -- another vista not visible from Earth. Pictured are many of Saturn's photogenic wonders, including the subtle colors of cloud bands, the complex shadows of the rings on the planet, the shadow of the planet on the rings, and the moons Mimas (2 o'clock), Janus (4 o'clock), and Pandora (8 o'clock). As Saturn moves towards equinox in 2009, the ring shadows are becoming smaller and moving toward the equator. During equinox, the rings will be nearly invisible from Earth and project only an extremely thin shadow line onto the planet.

APOD: 2007 January 31 - Movie: Cassini Crosses Saturn's Ring Plane
Explanation: What would the rings of Saturn look like if you passed right through the ring plane? To find out, NASA aimed cameras from the Cassini spacecraft right at Saturn's rings as the robotic explorer passed from the sunlit side of the rings to the shadowed side. Resulting images from a vantage point outside the rings and most moons, but inside the orbit of Titan, have been gathered together in the above time-lapse movie. The dramatic movie demonstrates that ring particle density and reflectivity makes some parts of the shadowed side nearly the photographic negative of the sunlit side, but nearly empty regions remain continually dark. Visible also are Saturn-orbiting moons Enceladus, Mimas, Janus, Epimetheus, Prometheus, and Pandora. The extreme thinness of Saturn's rings can be appreciated from frames taken near the crossing time.

APOD: 2006 November 7 - Janus: Potato Shaped Moon of Saturn
Explanation: Janus is one of the stranger moons of Saturn. First, Janus travels in an unusual orbit around Saturn where it periodically trades places with its sister moon Epimetheus, which typically orbits about 50 kilometers away. Janus, although slightly larger than Epimetheus, is potato-shaped and has a largest diameter of about 190 kilometers. Next, Janus is covered with large craters but strangely appears to lack small craters. One possible reason for this is a fine dust that might cover the small moon, a surface also hypothesized for Pandora and Telesto. Pictured above, Janus was captured in front of the cloud tops of Saturn in late September.

APOD: 2005 November 2 - Epimetheus and Janus: Interchangeable Moons of Saturn
Explanation: These two moons change places. Epimetheus and Janus, two small moons of Saturn, actually switch positions as they orbit their home planet. The orbital radii of the moons are strangely separated by less than the radii of the moons themselves: about 50 kilometers. One moon orbits Saturn well ahead of the other, at first. As the two moons gravitationally attract, they approach each other and, every few years, actually pass and trade orbits. This strange dance creates speculation that Epimetheus and Janus were once joined and later split from each other. Pictured above, the two moons were photographed rounding their orbits just outside of Saturn's F ring. The above image was taken in early September by the robot Cassini spacecraft, also orbiting Saturn.

APOD: 2005 August 24 - Epimetheus: A Small Moon of Saturn
Explanation: How did Epimetheus form? No one is yet sure. To help answer that question, this small moon has recently been imaged again in great detail by the robot spacecraft Cassini now orbiting Saturn. Epimetheus sometimes orbits Saturn in front of Janus, another small satellite, but sometimes behind. The above false-color image, taken during mid July, shows a surface covered with craters indicating great age. Epimetheus spans about 115 kilometers across. Epimetheus does not have enough surface gravity to restructure itself into a sphere.

APOD: 2005 April 29 - Small Moon Epimetheus
Explanation: Small saturnian moon Epimetheus (ep-ee-MEE-thee-us) is at most 116 kilometers across. Its cratered surface and irregular shape are highlighted by dramatic shadows in this composite close-up image from the Cassini spacecraft. However, orbiting 91,000 kilometers above Saturn's cloud tops, Epimetheus is not alone. Similar in size, saturnian moon Janus occupies an orbit separated from Epimetheus' by only about 50 kilometers. The two actually approach each other once every four years, but instead of colliding, the moons deftly exchange orbits and move apart again! In fact, co-orbiting Epimetheus and Janus both consist mostly of porous water ice and could have formed from the breakup of a single parent body. The small moons are also believed to play a role in maintaining the outer edge of Saturn's A ring.

APOD: 2004 July 21 - A Shadow on the Rings of Saturn
Explanation: This picture of Saturn could not have been taken from Earth. No Earth based picture could possibly view the night side of Saturn and the corresponding shadow cast across Saturn's rings. Since Earth is much closer to the Sun than Saturn, only the day side of the planet is visible from the Earth. Rather, this picture was taken by the robot Cassini spacecraft that began orbiting Saturn earlier this month. The dark western limb of Saturn looms large on the image right, while complex concentrations of small ring particles reflect sunlight on the image left. Saturn's enigmatic F ring is visible around the outside, showing mysterious knots. The small moon Epimetheus, only about 100 kilometers across, can also been seen on the far left. Cassini is scheduled to drop a probe toward the largest moon Titan in December.

APOD: October 18, 1998 - Saturns Rings Seen Sideways
Explanation: Saturn's rings are actually very thin. This picture from the Hubble Space Telescope was taken on August 6, 1995 when the rings lined up sideways as seen from Earth. Saturn's largest moon Titan is seen on the left, and Titan's shadow can be seen on Saturn's cloud tops! Titan itself looks a brownish color because of its thick atmosphere. Four other moons of Saturn can be seen just above the ring plane, which are, from left to right: Mimas, Tethys, Janus, and Enceladus. If you look carefully, you will note that the dark band across the planet is actually the shadow of the rings, and is slightly displaced from the real rings - which are best seen away from the planet. Saturn's rings are not solid - they are composed of ice chunks which range in size from a grain of sand to a house.

APOD: May 24, 1997 - Saturn's Rings Seen Sideways
Explanation: Saturn's rings are actually very thin. This picture from the Hubble Space Telescope was taken on August 6, 1995 when the rings lined up sideways as seen from Earth. Saturn's largest moon Titan is seen on the left, and Titan's shadow can be seen on Saturn's cloud tops! Titan itself looks a brownish color because of its thick atmosphere. Four other moon's of Saturn can be seen just above the ring plane, which are, from left to right: Mimas, Tethys, Janus, and Enceladus. If you look carefully, you will note that the dark band across the planet is actually the shadow of the rings, and is slightly displaced from the real rings - which are best seen away from the planet. Saturn's rings are not solid - they are composed of ice chunks which range in size from a grain of sand to a house.

APOD: May 12, 1996 - Tracking Saturn's Moons
Explanation: These five pairs of Hubble Space Telescope images track some of Saturn's moons as they orbit the ringed planet. A pair of images was taken every 97 minutes on November 21, 1995 with the Wide Field Planetary Camera-2, the normally bright ring system appearing nearly edge-on. In the top pair, the large bright moon Dione hangs above center while the smaller moons Pandora, Prometheus, and Mimas (top right image) appear near the planet's disk close to the outer ring. By the second and third pair of images, moons Rhea and Epimetheus have joined the dance. During the Saturn ring plane crossings, the reduction in light from the edge-on rings provided an opportunity for astronomer's to explore Saturn's complex moon system and search for elusive undiscovered satellites.

APOD: April 29, 1996 - Saturn's Rings Seen Sideways
Explanation: Saturn's rings are actually very thin. This picture from the Hubble Space Telescope was taken on August 6, 1995 when the rings lined up sideways as seen from Earth. Saturn's largest moon Titan is seen on the left, and Titan's shadow can be seen on Saturn's cloud tops! Titan itself looks a brownish color because of its thick atmosphere. Four other moon's of Saturn can be seen just above the ring plane, which are, from left to right: Mimas, Tethys, Janus, and Enceladus. If you look carefully, you will note that the dark band across the planet is actually the shadow of the rings, and is slightly displaced from the real rings - which are best seen away from the planet. Saturn's rings are not solid - they are composed of ice chunks which range in size from a grain of sand to a house.