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Moon of Goddard Space Flight Center (GSFC) and Saturn
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Natural Saturn On The Cassin
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| Title |
Natural Saturn On The Cassini Cruise |
| Explanation |
What could you see approaching Saturn [ http://www.jpl.nasa.gov/cassini/Kids/stories/ ] aboard an interplanetary cruise [ http://www.jpl.nasa.gov:80/cassini/Mission/cruise.html ] ship? Your view would likely resemble this subtly shaded image [ http://oposite.stsci.edu/pubinfo/pr/1998/28/b.html ] of the gorgeous ringed gas giant. Processed by the Hubble Heritage project [ http://heritage.stsci.edu/ ], the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn [ http://heritage.stsci.edu/ public/Oct22/saturn/saturntable.html#caption ] with cloud bands, storms [ http://antwrp.gsfc.nasa.gov/apod/ap951018.html ], nearly edge-on rings [ http://antwrp.gsfc.nasa.gov/apod/ap981018.html ], and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently enroute [ http://www.jpl.nasa.gov/cassini/ ] - the Cassini spacecraft, launched in 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and scheduled to arrive at Saturn [ http://www.jpl.nasa.gov/cassini/today/ ] in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960727.html ], Cassini will tour the Saturnian system [ http://www.hawastsoc.org/solar/eng/saturn.htm ], conducting a remote, robotic exploration with software and instruments designed by [ http://www.jpl.nasa.gov/cassini/Partners/ ] denizens of planet Earth. But where is Cassini now [ http://www.jpl.nasa.gov/cassini/today/ ]? Still about 980 million kilometers from Saturn, last Sunday the spacecraft flew by asteroid 2685 Masursky [ http://www.jpl.nasa.gov/cassini/MoreInfo/ sigevents/sigevent000128.html ]. |
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Stereo Saturn
| Title |
Stereo Saturn |
| Explanation |
Get out your red/blue glasses [ http://img.arc.nasa.gov/archive/desert96/redblue.html ] and launch [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] yourself into this stereo [ http://cass.jsc.nasa.gov/research/stereo_atlas/SS3D.HTM ] picture of Saturn! The picture is actually composed from two images recorded weeks apart by the Voyager 2 spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] during its visit to [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] the Saturnian System in August of 1981. Traveling at about 35,000 miles per hour, the spacecraft's changing viewpoint from one image to the next produced this exaggerated but pleasing stereo effect [ http://antwrp.gsfc.nasa.gov/apod/ap970404.html ]. Saturn is the second largest planet [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/saturn.html ] in the Solar System, after Jupiter. Its spectacular ring system [ http://ringmaster.arc.nasa.gov/saturn/saturn.html ] is so wide that it would span the space between the Earth and Moon. Although they look solid here, Saturn's [ http://antwrp.gsfc.nasa.gov/apod/ap000129.html ] rings consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders. |
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Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://www.seds.org/nineplanets/nineplanets/mercury.html ]'s old surface is heavily cratered [ http://liftoff.msfc.nasa.gov/Academy/SPACE/SolarSystem/Meteors/Craters.html ] like many moons. Mercury [ http://www.solarviews.com/eng/mercury.htm ] is larger than most moons but smaller than Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap990806.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap990304.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap960717.html ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ]. Mercury is much denser and more massive than any moon, though, because it is made mostly of iron. In fact, the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ] is the only planet more dense. A visitor to Mercury's surface [ http://antwrp.gsfc.nasa.gov/apod/ap960121.html ] would see some strange sights. Because Mercury [ http://www.oulu.fi/~spaceweb/textbook/mercury.html ] rotates exactly three times every two orbits around the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap951004.html ], and because Mercury [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-mercury.html ]'s orbit is so elliptical, a visitor to Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap990102.html ] might see the Sun [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/interv.html ] rise, stop in the sky, go back toward the rising horizon [ http://antwrp.gsfc.nasa.gov/apod/ap990619.html ], stop again, and then set quickly over the other horizon. From Earth [ http://antwrp.gsfc.nasa.gov/apod/ap980530.html ], Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ] cause it to be visible only for a short time just after sunset or just before sunrise. |
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Sky and Planets
| Title |
Sky and Planets |
| Explanation |
On February 10th, an evocative [ http://www.jps.net/ssumner/ ] evening sky above Rocklin, California, USA inspired astrophotographer Steve Sumner to record this remarkable sight - five planets and the Moon. Near its first quarter phase, the bright Moon [ http://lunar.arc.nasa.gov/ ] was intentionally overexposed but Saturn [ http://www.jpl.nasa.gov/cassini/ ], Jupiter [ http://galileo.jpl.nasa.gov/ ], Mars [ http://mars.jpl.nasa.gov/ ], and Mercury [ http://sd-www.jhuapl.edu/MESSENGER/ ] (and, of course, planet Earth's [ http://www.earth.nasa.gov/ ] horizon) are all clearly visible in the deepening twilight. Notably absent in this grouping of naked-eye planets is Venus [ http://antwrp.gsfc.nasa.gov/apod/ap990903.html ] which is still putting in an early appearance as the morning star [ http://ispec.scibernet.com/station/morn_star.html ]. This month, Mercury has joined Venus in the dawn twilight while Saturn, Jupiter, and Mars still shine brightly in the western sky at nightfall [ http://www.skypub.com/sights/sights.shtml ] making another gorgeous close grouping with the crescent Moon [ http://www.inconstantmoon.com/ ]. |
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Slightly Beneath Saturn's Ri
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| Title |
Slightly Beneath Saturn's Ring Plane |
| Explanation |
When orbiting Saturn, be sure to watch for breathtaking superpositions of moon [ http://antwrp.gsfc.nasa.gov/apod/ap051003.html ]s, rings [ http://antwrp.gsfc.nasa.gov/apod/ap040117.html ], and shadow [ http://antwrp.gsfc.nasa.gov/apod/ap040803.html ]s. One such picturesque vista [ http://photojournal.jpl.nasa.gov/catalog/PIA08146 ] was visible recently to the robot Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini-Huygens ] now orbiting Saturn. In late February, Cassini captured Rhea [ http://en.wikipedia.org/wiki/Rhea_%28moon%29 ], the second largest moon of Saturn, while looking up from slightly beneath Saturn's expansive ring [ http://antwrp.gsfc.nasa.gov/apod/ap051219.html ] plane. Signature dark gaps [ http://www.planetary.org/saturn/rings.html ] are visible in the nearly edge-on rings. A shadow of Saturn's F ring [ http://antwrp.gsfc.nasa.gov/apod/ap041217.html ] cuts across the cratered ice-moon. Cassini is scheduled [ http://saturn.jpl.nasa.gov/operations/saturn-tour.cfm ] to continue sending back images from the orbit of Saturn until at least 2008. |
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Venus, Moon, and Neighbors
| Title |
Venus, Moon, and Neighbors |
| Explanation |
Rising before the Sun on February 2nd, astrophotographer [ http://pages.prodigy.net/pam.orman/JoeGallery.html ] Joe Orman anticipated [ http://pages.prodigy.net/pam.orman/JoeAlmanac2000.html ] this apparition of the bright morning star [ http://ispec.scibernet.com/station/morn_star.html ] Venus near a lovely crescent Moon above a neighbor's house in suburban Phoenix, Arizona, USA. Fortunately, the alignment of bright planets and the Moon is one of the most inspiring sights in the night sky [ http://www.skypub.com/sights/skyevents/0004skyevents.html ] and one that is often easy to enjoy and share without any special equipment. Take tonight [ http://spacescience.com/headlines/y2000/ast30mar_1m.htm ], for example. Those blessed with clear skies can simply step outside near sunset and view a young crescent Moon very near three bright planets in the west Jupiter [ http://galileo.jpl.nasa.gov/ ], Mars [ http://mars.jpl.nasa.gov/mgs/ ], and Saturn [ http://www.jpl.nasa.gov/cassini/ ]. Jupiter will be the unmistakable brightest star near the Moon with a reddish Mars just to Jupiter's north and pale yellow Saturn directly above. Of course, these sky shows [ http://drumright.ossm.edu/astronomy/conjunctions.html ] create an evocative picture [ http://antwrp.gsfc.nasa.gov/apod/ap000310.html ] but the planets and Moon just appear to be near each other -- they are actually only approximately lined up and lie in widely separated orbits. Unfortunately, next month's highly publicized alignment of planets [ http://www.griffithobs.org/SkyAlignments.html ] on May 5th will be lost from view in the Sun's glare but such planetary alignments [ http://www.skypub.com/news/special/whypanic.html ] occur repeatedly and pose no danger [ http://www.badastronomy.com/bad/misc/planets.html ] to planet Earth. |
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Descent Panorama of Saturn's
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| Title |
Descent Panorama of Saturn's Titan |
| Explanation |
You're the first spacecraft ever to descend to Titan -- what do you see? Immediately after the Huygen's probe [ http://en.wikipedia.org/wiki/Huygens_probe ] pierced the cloud deck of Saturn [ http://en.wikipedia.org/wiki/Saturn_%28planet%29 ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?titan ] last January, it took a unique series of pictures of one of the Solar System [ http://www.windows.ucar.edu/our_solar_system/solar_system.html ]'s most mysterious moon's. Those pictures have recently been digitally stitched together to create spectacular panoramas and a dramatic descent movie [ http://photojournal.jpl.nasa.gov/catalog/PIA08117 ]. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08114 ] is a panoramic fisheye view Huygen's obtained from about five kilometers above Titan's surface [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ]. The digital projection makes the local surface, mostly flat, appear as a ball, but allows one to see in all directions. Huygen's eventual landing site [ http://antwrp.gsfc.nasa.gov/apod/ap050518.html ] was in the large dark area below, just right of the center. This relatively featureless, dark, sandy basin appears to be surrounded by light colored hills to the right and a landscape fractured by streambeds and canyons [ http://antwrp.gsfc.nasa.gov/apod/ap050124.html ] above. Recent evidence [ http://uanews.org/cgi-bin/WebObjects/UANews.woa/16/wa/MainStoryDetails?ArticleID=12614 ] indicates that Titan's lakebeds and streambeds are usually dry but sometimes filled with a flashflood of liquid methane [ http://en.wikipedia.org/wiki/Methane ] from rare torrents of methane rain [ http://www.astrobio.net/news/article1413.html ]. |
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Saturn in Blue and Gold
| Title |
Saturn in Blue and Gold |
| Explanation |
Why is Saturn partly blue? The above picture [ http://photojournal.jpl.nasa.gov/catalog/PIA08166 ] of Saturn approximates what a human [ http://en.wikipedia.org/wiki/Human ] would see if hovering close to the giant ringed world. The above picture [ http://photojournal.jpl.nasa.gov/catalog/PIA08166 ] was taken in mid-March by the robot Cassini spacecraft [ http://www.esa.int/esaMI/Cassini-Huygens/SEM9D2HHZTD_0.html ] now orbiting Saturn [ http://www.nineplanets.org/saturn.html ]. Here Saturn's majestic rings [ http://en.wikipedia.org/wiki/Saturn%27s_rings ] appear directly only as a thin vertical line. The rings show their complex structure in the dark shadows they create on the image left. Saturn's fountain moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ], only about 500 kilometers across, is seen as the bump in the plane of the rings. The northern hemisphere of Saturn can appear partly blue [ http://science.nasa.gov/headlines/y2005/17feb_bluesaturn.htm ] for the same reason that Earth's skies can appear blue [ http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html ] -- molecules in the cloudless portions of both planet's atmospheres are better at scattering blue light than red. When looking deep into Saturn's clouds [ http://antwrp.gsfc.nasa.gov/apod/ap051010.html ], however, the natural gold hue of Saturn's clouds becomes dominant. It is not known why "southern" Saturn does not show the same blue hue -- one hypothesis holds that clouds are higher there. It is also not known [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004cosp.meet..466W ] why Saturn's clouds are colored [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ] gold. |
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Planets Above The Clouds
| Title |
Planets Above The Clouds |
| Explanation |
Clouds scatter the faint orange rays of the setting sun [ http://antwrp.gsfc.nasa.gov/apod/ap000115.html ] in the foreground of this breathtaking photograph from the summit [ http://www.ifa.hawaii.edu/mko/mko.html ] of Mauna Kea, Hawaii [ http://antwrp.gsfc.nasa.gov/apod/ap980725.html ]. Taken on April 7th, this skyscape features a dramatic lunar and planetary alignment [ http://antwrp.gsfc.nasa.gov/apod/ap000406.html ]. An overexposed crescent moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ] dominates the celestial scene, but the bright "star" just below and to its right is Saturn [ http://www.jpl.nasa.gov/cassini/Kids/stories/ ] while further below Saturn is a close pairing of brilliant Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] and a fainter, yellowish Mars [ http://marsnt3.jpl.nasa.gov/education/students.html ]. Red giant star Aldebaran [ http://www.bo.astro.it/copernic/alde-eng.html ] is almost directly above the moon near the top of the image and the bright blue stars of the Pleiades cluster [ http://www.aao.gov.au/images.html/captions/uks018.html ] are visible about midway up and to the right of the moon-Aldebaran line. The good news is that planetary alignments [ http://www.skypub.com/news/special/whypanic.html ] like this one do not portend [ http://tech-two.mit.edu/Shakespeare/Tragedy/macbeth/ macbeth.html ] disasters, are relatively common, and can clearly make inspirational viewing for casual stargazers and astronomers alike. The bad [ http://www.badastronomy.com/bad/misc/planets.html ] news is that the world is not going to end because of the highly publicized planetary alignment [ http://www.griffithobs.org/SkyAlignments.html ] occurring tomorrow, May 5th -- so you probably will have to go to work [ http://www.nasa.gov/newsinfo/alignment.html ]! |
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Ancient Craters on Saturn's
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| Title |
Ancient Craters on Saturn's Rhea |
| Explanation |
Saturn's ragged moon Rhea has one of the oldest surfaces known. Estimated as changing little in the past billion years, Rhea [ http://en.wikipedia.org/wiki/Rhea_%28moon%29 ] shows craters [ http://en.wikipedia.org/wiki/Impact_crater ] so old they no longer appear round ? their edges have become compromised by more recent cratering. Like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap051113.html ], Rhea's rotation is locked on Saturn, and the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08173 ] shows part of Rhea's surface [ http://antwrp.gsfc.nasa.gov/apod/ap051213.html ] that always faces Saturn. Rhea's leading surface is more highly cratered than its trailing surface. Rhea [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?rhea ] is composed mostly of water-ice but is thought to have a small rocky core. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08173 ] was taken by the robot Cassini spacecraft [ http://www.esa.int/esaMI/Cassini-Huygens/SEM9D2HHZTD_0.html ] now orbiting Saturn. Cassini swooped past Rhea two months ago and captured the above image from about 100,000 kilometers away. Rhea [ http://www.nineplanets.org/rhea.html ] spans 1,500 kilometers making it Saturn's second largest moon after Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060215.html ]. Several surface features on Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap050215.html ] remain unexplained including large light patch [ http://antwrp.gsfc.nasa.gov/apod/ap050530.html ]es. |
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Crescent Rhea Occults Cresce
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| Title |
Crescent Rhea Occults Crescent Saturn |
| Explanation |
Soft hues, partially lit orbs, a thin trace of the ring, and slight shadows highlight this understated view of the majestic surroundings of the giant planet Saturn. Looking nearly back toward the Sun, the robot Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini-Huygens ] now orbiting Saturn captured crescent phases [ http://antwrp.gsfc.nasa.gov/apod/ap060618.html ] of Saturn [ http://www.nineplanets.org/saturn.html ] and its moon Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap060530.html ] in color a few months ago. As striking as the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA07806 ] is, it is but a single frame from a recently released 60-frame silent movie where Rhea can be seen gliding in front of its parent world. Since Cassini was nearly in the plane of Saturn's rings [ http://pds-rings.seti.org/saturn/ ], the normally impressive rings are visible here only as a thin line [ http://antwrp.gsfc.nasa.gov/apod/ap051219.html ] across the image center. Cassini has now passed the official half-way mark of its mission around Saturn, but is well situated to complete another two years [ http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=670 ] investigating this complex and surprising system. |
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Planets In The Sun
| Title |
Planets In The Sun |
| Explanation |
Today [ http://science.nasa.gov/headlines/y2000/ast02may_1.htm ], all five naked-eye planets [ http://www.seds.org/nineplanets/nineplanets/ ] (Mercury, Venus, Mars, Jupiter, Saturn) plus the Moon and the Sun [ http://helios.gsfc.nasa.gov/ sun.html ] will at least approximately line-up. As viewed [ http://drumright.ossm.edu/astronomy/conjunctions.html ] from planet Earth, they will be clustered within about 26 degrees, the closest alignment for all these celestial bodies [ http://science.nasa.gov/headlines/y2000/ ast30mar_1m.htm#alignments ] since February 1962, when there was a solar eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap990818.html ]! Such planetary alignments [ http://www.griffithobs.org/SkyAlignments.html ] are not dangerous, except of course that the Sun might hurt your eyes when you look at it [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ]. So it might be easier [ http://sohowww.nascom.nasa.gov/hotshots/ ] to appreciate today's solar system [ http://space.jpl.nasa.gov/ ] spectacle if |
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Methane Rain Possible on Tit
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| Title |
Methane Rain Possible on Titan |
| Explanation |
Might it rain cold methane on Saturn's Titan? Recent analyses [ http://www.nature.com/news/2006/060724/full/060724-7.html ] of measurements taken by the Huygen's probe [ http://antwrp.gsfc.nasa.gov/apod/ap060131.html ] that landed on Titan [ http://en.wikipedia.org/wiki/Titan_%28moon%29 ] in 2005 January indicate that the atmosphere is actually saturated with methane [ http://en.wikipedia.org/wiki/Methane ] at a height of about 8 kilometers. Combined with observations of a damp surface [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ] and lakes [ http://antwrp.gsfc.nasa.gov/apod/ap060731.html ] near the poles, some astrobiologists conclude that at least a methane drizzle [ http://www.nasa.gov/centers/ames/news/releases/2006/06_57AR.html ] is common on parts of Titan. Other astrobiologists reported [ http://www.nature.com/nature/journal/v442/n7101/abs/nature04933.html ] computer models of the clouded moon that indicate that violent methane storms might even occur, complete with flash floods carving channels [ http://antwrp.gsfc.nasa.gov/apod/ap060508.html ] in the landscape. The later scenario is depicted in the above drawing of Titan. Lightning [ http://antwrp.gsfc.nasa.gov/apod/ap040818.html ], as also depicted above, might well exist on Titan but has not been proven. The findings [ http://www.planetary.org/blog/article/00000658/ ] increase speculation that a wet Titanian surface [ http://www.astrobio.net/news/article1766.html ] might be hospitable to unusual forms of life [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..178..274M ]. |
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The Last Moon Shot
| Title |
The Last Moon Shot |
| Explanation |
In 1865 Jules Verne [ http://www.interlog.com/~anash/najvs.html ] predicted the invention of a space capsule that could carry people. In his science fiction story "From the Earth to the Moon" [ http://JV.Gilead.org.il/pg/moon/ ], he outlined his vision of a cannon in Florida so powerful that it could shoot a "Projectile-Vehicle" [ http://www.nasm.edu/galleries/gal109/NEWHTF/ITM6201.HTM ] carrying three adventurers to the Moon [ http://www.hq.nasa.gov/office/pao/History/ ap11ann/eagle.html ]. Over 100 years later, NASA [ http://www.hq.nasa.gov/pao/History/history.html ], guided by Wernher Von Braun [ http://history.msfc.nasa.gov/vonbraun/index.html ]'s vision, produced the Saturn V rocket [ http://www.apollosaturn.com/ ]. From a spaceport in Florida [ http://www.ksc.nasa.gov/ksc.html ], this rocket turned Verne's fiction into fact, launching 9 Apollo Lunar missions and allowing 12 astronauts to walk on the Moon [ http://www.hq.nasa.gov/office/pao/History/alsj/ ]. Pictured [ http://images.jsc.nasa.gov/images/pao/AS17/10075937.htm ] is the last moon shot, Apollo 17 [ http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo17info.html ], awaiting a night launch in December of 1972. Spotlights play on the rocket and launch pad while the full Moon looms [ http://cass.jsc.nasa.gov/moon.html ] in the background. Humans have not walked on [ http://www.hq.nasa.gov/office/pao/History/alsj/ apollo.epilog.html ] on the lunar surface since. [ http://ilewg.jsc.nasa.gov/ ] |
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Bright Cliffs Across Saturn'
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| Title |
Bright Cliffs Across Saturn's Moon Dione |
| Explanation |
What causes the bright streaks on Dione? Recent images of this unusual moon by the robot Cassini spacecraft [ http://saturn.jpl.nasa.gov/overview/mission.cfm ] now orbiting Saturn [ http://www.nineplanets.org/saturn.html ] are helping to crack the mystery. Close inspection of Dione's trailing hemisphere, pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08256 ], indicates that the white wisps are composed of deep ice cliffs [ http://antwrp.gsfc.nasa.gov/apod/ap051026.html ] dropping hundreds of meters. The cliffs may indicate that Dione has undergone some sort of tectonic surface [ http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html ] displacements in its past. The bright ice-cliffs run across some of Dione [ http://en.wikipedia.org/wiki/Dione_%28moon%29 ]'s many craters, indicating that the process [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1984Icar...59..205M ] that created them occurred later than the impacts [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] that created those craters. Dione [ http://www.nineplanets.org/dione.html ] is made of mostly water ice but its relatively high density indicates that it contains much rock [ http://en.wikipedia.org/wiki/Rock_and_roll ] inside. Giovanni Cassini [ http://www.seds.org/messier/xtra/Bios/cassini.html ] discovered Dione in 1684. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08256 ] was taken at the end of July from a distance of about 263,000 kilometers. Other high resolution image [ http://antwrp.gsfc.nasa.gov/apod/ap951009.html ]s of Dione were taken by the passing Voyager spacecraft [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] in 1980. |
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Moon And Venus Share The Sky
| Title |
Moon And Venus Share The Sky |
| Explanation |
July is drawing to a close and in the past few days, some early morning risers [ http://antwrp.gsfc.nasa.gov/apod/ap990714.html ] could have looked east and seen a crescent Moon sharing the pre-dawn [ http://science.nasa.gov/headlines/y2000/ast25jul_1m.htm ] skies with planets Jupiter and Saturn. Planet Mercury will also pass about 2 degrees from the thin waning crescent Moon [ http://aa.usno.navy.mil/AA/faq/docs/moon_phases.html ] just before sunrise near the eastern horizon on Saturday, July 29. And finally, on the evening of July 31st, Venus will take its turn near the crescent Moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ]. But this time it will be a day-old crescent Moon near the western horizon, shortly after sunset [ http://antwrp.gsfc.nasa.gov/apod/ap000507.html ]. In fact [ http://pages.prodigy.net/pam.orman/JoeAlmanac2000.html ], on July 31 (August 1 Universal Time) the Moon will occult [ http://www.skypub.com/sights/occultations/lunar/ 0001lunarocc.html ] (pass in front of) Venus for northwestern observers [ http://www.skypub.com/sights/images2000/ 0008moonvenus_big.jpg ] in North America. This telescopic picture taken on 31 December 1997, shows a lovely young crescent Moon and brilliant crescent Venus in [ http://antwrp.gsfc.nasa.gov/apod/ap990903.html ] the early evening sky near Bursa, Turkey [ http://www.mersina.com/Turkey/Marmara/Bursa/index.html ]. And what about the Sun? On Sunday, July 30, a partial eclipse of the Sun [ http://sunearth.gsfc.nasa.gov/eclipse/extra/ PSE2000Jul31.html ] will be visible from some locations [ http://sunearth.gsfc.nasa.gov/eclipse/OH/ PSE2000Jul.gif ] in North America. |
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Earth from Saturn
| Title |
Earth from Saturn |
| Explanation |
What's that pale blue dot in this image taken from Saturn? Earth [ http://antwrp.gsfc.nasa.gov/apod/ap010204.html ]. The robotic Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/index.cfm ] looked back toward its old home world earlier this month as it orbited Saturn [ http://en.wikipedia.org/wiki/Saturn_(planet) ]. Using Saturn itself to block the bright Sun [ http://antwrp.gsfc.nasa.gov/apod/ap030530.html ], Cassini imaged a faint dot on the right of the above photograph [ http://photojournal.jpl.nasa.gov/catalog/PIA08324 ]. That dot is expanded on the image inset, where a slight elongation in the direction of Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap030526.html ] is visible [ http://antwrp.gsfc.nasa.gov/apod/ap980904.html ]. Vast water oceans make Earth's reflection of sunlight somewhat blue [ http://www.sciam.com/askexpert_question.cfm?articleID=000CCDD2-DD07-1C71-9EB7809EC588F2D7 ]. Earth is home to over six billion humans [ http://desip.igc.org/populationmaps.html ] and over one octillion [ http://en.wikipedia.org/wiki/Octillion ] Prochlorococcus [ http://sciam.com/article.cfm?chanID=sa022&articleID=0005BE47-0078-1FA8-807883414B7F0000 ]. |
|
In the Shadow of Saturn
| Title |
In the Shadow of Saturn |
| Explanation |
In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/index.cfm ] now orbiting Saturn [ http://antwrp.gsfc.nasa.gov/apod/saturn.html ] recently drifted in giant planet's shadow [ http://antwrp.gsfc.nasa.gov/apod/ap040926.html ] for about 12 hours and looked back toward the eclipsed Sun [ http://antwrp.gsfc.nasa.gov/apod/ap010408.html ]. Cassini saw a view unlike any other. First, the night side of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap060912.html ] is seen to be partly lit by light reflected from its own majestic ring system [ http://www.planetary.org/saturn/images_saturn_rings.html ]. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn and slightly scattering [ http://www.daviddarling.info/encyclopedia/F/forward_scattering.html ] sunlight, in the above exaggerated color image [ http://photojournal.jpl.nasa.gov/catalog/PIA08329 ]. Saturn's rings light up so much that new rings [ http://photojournal.jpl.nasa.gov/catalog/PIA08322 ] were discovered, although they are hard to see in the above image. Visible in spectacular detail, however, is Saturn's E ring [ http://www.planetary.org/explore/topics/saturn/rings.html ], the ring created by the newly discovered ice-fountains [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] of the moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap050906.html ], and the outermost ring visible above. Far in the distance [ http://antwrp.gsfc.nasa.gov/apod/ap060927.html ], visible on the image left just above the bright main rings, is the almost ignorable pale blue dot [ http://en.wikipedia.org/wiki/Pale_Blue_Dot ] of Earth. |
|
The Surface of Titan
| Title |
The Surface of Titan |
| Explanation |
If sailing the hydrocarbon [ http://chemscape.santafe.cc.fl.us/chemscape/glossary/hdef.htm#24 ] seas of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ], beware of gasoline rain. Such might be a travel advisory [ http://travel.state.gov/travel_warnings.html ] issued one future day for adventurers visiting Titan [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html http://www.seds.org/nineplanets/nineplanets/titan.html ], the largest moon of Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ]. New images of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap951021.html ]'s surface were released [ http://despa.obspm.fr/planeto/titan_pueo.html ] last week from the Canada-France Hawaii Telescope [ http://www.cfht.hawaii.edu/ ] featuring the finest details [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999DPS....31.4103C ] yet resolved. Peering into Titan [ http://ispec.scibernet.com/student-pages/saturn/titan.html ]'s thick smog [ http://www.aqmd.gov/smog/inhealth.html ] atmosphere with infrared [ http://www.us-gemini.noao.edu/public/infrared.html ] light, complex features interpreted as oceans, glaciers [ http://uanews.opi.arizona.edu/cgi-bin/WebObjects/ScienceResearch.woa/wo/XoEuK0m1padNGJ00ob/0.11.0.3?ArticleID=1926 ], and rock became visible. The high-resolution infrared image pictured above [ http://despa.obspm.fr/planeto/titan_pueo.html ] was made possible using an unblurring [ http://antwrp.gsfc.nasa.gov/apod/ap000725.html ] technique called adaptive optics [ http://www.lyot.obspm.fr/adaptive_optics.html ]. The interplanetary probe Cassini [ http://www.jpl.nasa.gov/cassini/ ] will reach Saturn and Titan in 2004 to better explore [ http://antwrp.gsfc.nasa.gov/apod/ap970829.html ] this unusual world. |
|
Janus: Potato Shaped Moon of
…
| Title |
Janus: Potato Shaped Moon of Saturn |
| Explanation |
Janus is one of the stranger moons of Saturn. First, Janus [ http://www.planetary.org/explore/topics/saturn/janus.html ] travels in an unusual orbit around Saturn where it periodically trades places with its sister moon Epimetheus [ http://antwrp.gsfc.nasa.gov/apod/ap050429.html ], which typically orbits about 50 kilometers away. Janus [ http://en.wikipedia.org/wiki/Janus_%28moon%29 ], although slightly larger than Epimetheus [ http://antwrp.gsfc.nasa.gov/apod/ap050824.html ], is potato [ http://en.wikipedia.org/wiki/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 [ http://antwrp.gsfc.nasa.gov/apod/ap051123.html ] and Telesto [ http://antwrp.gsfc.nasa.gov/apod/ap060222.html ]. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08296 ], Janus was captured in front of the cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap051010.html ] of Saturn [ http://en.wikipedia.org/wiki/Saturn ] in late September. |
|
Mountains of Titan
| Title |
Mountains of Titan |
| Explanation |
Peering through [ http://www.jpl.nasa.gov/news/news.cfm?release=2006-147 ] the thick, hazy atmosphere of Saturn's largest moon, an infrared camera onboard the Cassini [ http://saturn.jpl.nasa.gov/home/index.cfm ] spacecraft recorded this view of the tallest mountains ever seen on Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060508.html ]. Captured during a flyby in late October, the high resolution, false-color mosaic [ http://photojournal.jpl.nasa.gov/catalog/PIA09032 ] shows a mountain range about 150 kilometers long and about 1.5 kilometers high - likened to the Sierra Nevada [ http://en.wikipedia.org/wiki/Sierra_Nevada_(US) ] mountain range of the western United States, planet Earth [ http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=11270 ]. Along Titan's mountain ridges lie bright deposits, thought to be methane [ http://www.astrobio.net/news/article1886.html ] snow or other organic material. The icy [ http://antwrp.gsfc.nasa.gov/apod/ap050610.html ] mountains of Titan were probably formed like Earth's mid-ocean ridges, from material welling up [ http://www.pbs.org/wgbh/aso/tryit/tectonics/ divergent.html ] to fill gaps created as surface tectonic plates [ http://www.ucmp.berkeley.edu/geology/tectonics.html ] spread apart. |
|
The Ecliptic Plane
| Title |
The Ecliptic Plane |
| Explanation |
The Plane of the Ecliptic is well illustrated in this picture from the 1994 lunar prospecting Clementine spacecraft. Clementine's star tracker camera image reveals (from right to left) the Moon [ http://lunar.arc.nasa.gov/ ] lit by Earthshine, the Sun's corona [ http://antwrp.gsfc.nasa.gov/apod/ap960530.html ] rising over the Moon's dark limb, and the planets Saturn [ http://www.jpl.nasa.gov/cassini/ ], Mars [ http://mars.jpl.nasa.gov/ ], and Mercury [ http://sd-www.jhuapl.edu/MESSENGER/ ]. The ecliptic plane is defined as the imaginary plane containing the Earth's orbit around the Sun. In the course of a year, the Sun's apparent path [ http://www.astro.wisc.edu/~dolan/constellations/extra/Zodiac.html ] through the sky lies in this plane. The Solar System's [ http://space.jpl.nasa.gov/ ] planetary bodies all tend to lie near this plane, since they were formed from the Sun's spinning, flattened, proto-planetary disk [ http://antwrp.gsfc.nasa.gov/apod/ap990611.html ]. The snapshot above nicely captures a momentary line-up looking out along this fundamental plane of our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap990505.html ]. |
|
Cassini Spacecraft Approache
…
| Title |
Cassini Spacecraft Approaches Jupiter |
| Explanation |
A new spacecraft has entered the outer Solar System: Cassini [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ]. Launched in 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and bound for Saturn in 2004, Cassini sent back the above image [ http://ciclops.lpl.arizona.edu/ciclops/Images_jupiter.html ] last week while approaching the giant planet Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]. Cassini [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ] joins the Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/mission.html] currently in orbit around Jupiter in studying the gas giant and its moons. In fact, observations [ http://www.jpl.nasa.gov/releases/2000/glextended.html ] involving both spacecraft [ http://www.jpl.nasa.gov/jupiterflyby/ ] simultaneously are planned in the coming months. This color picture [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02972 ] was taken when Cassini was 81.3 million kilometers from Jupiter. The alternating dark and bright bands characteristic of Jupiter's cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] can be easily seen. Jupiter's moon Europa [ http://antwrp.gsfc.nasa.gov/apod/ap000825.html ] is also seen at the far right of the image casting a round shadow on the planet. |
|
New Moons For Saturn
| Title |
New Moons For Saturn |
| Explanation |
Which planet has the most moons? For now, it's Saturn. Four newly discovered [ http://www.eso.org/outreach/press-rel/pr-2000/ phot-29-00.html ] satellites bring the ringed planet's total to twenty-two, just edging out Uranus' [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ] twenty-one for the most known [ http://www.eso.org/outreach/press-rel/pr-2000/ phot-19-00.html ] moons in the solar system. Of course, the newfound Saturnian satellites [ http://www.nasm.edu/ceps/etp/saturn/satmoons.html ] are not large [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html ] and photogenic [ http://antwrp.gsfc.nasa.gov/apod/ap000129.html ]. The faint S/2000 S 1, the first discovered in the year 2000, is the tiny dot indicated at the lower right of this August 7th image made with the ESO 2.2 meter telescope at La Silla, Chile [ http://www.ls.eso.org/index.html ]. (An eye-catching spiral galaxy at the upper left is in the very distant background!) Unlike Saturn's larger moons whose almost circular orbits lie near the planet's equatorial plane, all four newly discovered moons have irregular [ http://www.obs-nice.fr/gladman/urhome.html ], skewed orbits drifting far from the planet. With sizes in the 10 to 50 kilometer range, they are are likely captured asteroids. The international team of astronomers involved in the discoveries hopes to get many observations of the tiny satellites [ http://www.obs-nice.fr/saturn/ ] allowing accurate orbital computations before Saturn is [ http://www.jpl.nasa.gov/cassini/ ] lost in the solar glare around March 2001. The team has also found several other irregular satellite candidates which are now being followed. Saturn's only previously known irregular satellite is Phoebe [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ phoebe.html ], discovered over 100 years ago by W. H. Pickering, |
|
A Year of Extraterrestrial F
…
| Title |
A Year of Extraterrestrial Fountains and Flows |
| Explanation |
The past year was extraordinary for the discovery of extraterrestrial fountains and flows -- some offering new potential in the search for liquid water and the origin of life beyond planet Earth.. Increased evidence was uncovered that fountains [ http://antwrp.gsfc.nasa.gov/apod/ap060608.html ] spurt not only from Saturn's moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ], but from the dunes of Mars [ http://antwrp.gsfc.nasa.gov/apod/ap060823.html ] as well. Lakes were found on Saturn's moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060731.html ], and the residual of a flowing liquid was discovered on the walls of Martian craters [ http://antwrp.gsfc.nasa.gov/apod/ap061212.html ]. The diverse Solar System [ http://en.wikipedia.org/wiki/Solar_system ] fluidity may involve forms of slushy water-ice, methane [ http://scifun.chem.wisc.edu/chemweek/methane/methane.html ], or sublimating [ http://en.wikipedia.org/wiki/ Sublimation_%28physics%29 ] carbon dioxide [ http://scifun.chem.wisc.edu/chemweek/CO2/CO2.html ]. Pictured above [ http://antwrp.gsfc.nasa.gov/apod/ap061231.html http://photojournal.jpl.nasa.gov/catalog/PIA09028 ], the light-colored path below the image center is hypothesized to have been created sometime in just the past few years by liquid water flowing [ http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html ] across the surface of Mars [ http://antwrp.gsfc.nasa.gov/apod/mars.html ]. |
|
Liquid Lakes on Saturn's Tit
…
| Title |
Liquid Lakes on Saturn's Titan |
| Explanation |
Why would some regions on Titan reflect very little radar? The leading explanation is that these regions are lakes, possibly composed of liquid methane. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA09102 ] is a false-color synthetic radar map of a northern region of Titan [ http://saturn.astrobio.net/news/article50.html ] taken during a flyby of the cloudy moon [ http://antwrp.gsfc.nasa.gov/apod/ap040810.html ] by the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini-Huygens ] last July. On this map, which spans about 150 kilometers across, dark regions reflect relatively little of the broadcast radar [ http://earth.rice.edu/mtpe/geo/geosphere/topics/remotesensing/25_radar.html ] signal. Images like this show Titan [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ] to be only the second body in the Solar System [ http://space.jpl.nasa.gov/ ] to possess liquids on the surface. Future observations from Cassini during Titan flybys [ http://saturn.jpl.nasa.gov/operations/saturn-tour.cfm ] will further test the methane [ http://en.wikipedia.org/wiki/Methane ] lake hypothesis, as comparative wind effects on the regions are studied. |
|
Jupiter Eyes Ganymede
| Title |
Jupiter Eyes Ganymede |
| Explanation |
Who keeps an eye [ http://ciclops.lpl.arizona.edu/ciclops/ images_jupiter.html ] on the largest moon in the Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ]? This moon, visible on the lower right, is Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and the planet it orbits, Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ], seems to be keeping a watchful eye, as its Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap960802.html ] appears serendipitously nearby. This recently released [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02837 ] enhanced-contrast image from the robot spacecraft Cassini [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] captures new details of the incredible intricacies of Jupiter's complex cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] patterns. Features as small as 250 kilometers can be seen. Counter-clockwise rotating high-pressure white ovals [ http://antwrp.gsfc.nasa.gov/apod/ap990105.html ] that are similar to the Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap001123.html ] appear in the red band below the spot. Between these spots are darker low-pressure systems [ http://www.usatoday.com/weather/wlowpres.htm ] that rotate clockwise. The hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] and helium [ http://pearl1.lanl.gov/periodic/elements/2.html ] that compose most of Jupiter's clouds is nearly invisible - the trace chemicals that give Jupiter these colors remain unknown [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ]. The Cassini spacecraft [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ] is using Jupiter [ http://www.hawastsoc.org/solar/eng/jupiter.htm ] to pull it [ http://www.science.nasa.gov/newhome/headlines/ast24jun99_1.htm#gravityassist ] toward Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], where it is scheduled [ http://www.jpl.nasa.gov/cassini/Mission/cruise.html ] to arrive in 2004. |
|
Jupiter, Europa, and Callist
…
| Title |
Jupiter, Europa, and Callisto |
| Explanation |
As the robot Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] rounds Jupiter [ http://www.jpl.nasa.gov/galileo/jupiter/jupiter.html ] on its way toward Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], it has taken a sequence of images [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] of the gas giant with its four largest moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. Previously released images have highlighted Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap001212.html ] and Io [ http://antwrp.gsfc.nasa.gov/apod/ap001226.html ]. Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02861 ] are the two remaining Galilean satellites [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ]: Europa [ http://www.hawastsoc.org/solar/eng/europa.htm ] and Callisto [ http://cass.jsc.nasa.gov/pub/research/outerp/call.html ]. Europa [ http://www.jpl.nasa.gov/galileo/moons/europa.html ] is the bright moon superposed near Jupiter's Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap001123.html ], while Callisto is the dark moon near the frame edge. Callisto [ http://www.jpl.nasa.gov/galileo/moons/callisto.html ] is so dark that it would be hard to see here if its brightness was not digitally enhanced. Recent evidence indicates [ http://www.jpl.nasa.gov/galileo/news/release/press001216.html ] 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 [ http://es.rice.edu/ES/humsoc/Galileo/Catalog/Files/roemer.html ] was able to make the first accurate estimation of the speed of light [ http://www.stats.uwaterloo.ca/~rwoldfor/papers/sci-method/paperrev/node4.html ]. |
|
Eclipse and Ecliptic
| Title |
Eclipse and Ecliptic |
| Explanation |
When [ http://www.inconstantmoon.com/cyc_phas.htm ] a Full Moon lies near the ecliptic there can be a lunar eclipse [ http://en.wikipedia.org/wiki/Lunar_eclipse ]. That cosmic alignment is well illustrated in this composite of eclipse images [ http://spaceweather.com/eclipses/ gallery_03mar07_page6.htm ] recorded last Saturday near Paris, France. The projection of the ecliptic plane [ http://antwrp.gsfc.nasa.gov/apod/ap050503.html ], the plane of planet Earth's orbit around the Sun, is traced by the long blue line running diagonally through the picture. At a small angle to the ecliptic, along the Moon's orbit, are a series of images from the eclipse itself following the Moon [ http://www.phy6.org/stargaze/Shipprc2.htm ] as it moves (down and left) through Earth's shadow [ http://www.pixheaven.net/photo_us.php?nom=070303_shadow ]. A small blue circle centered on the ecliptic outlines the extent of the dark region of the shadow or umbra [ http://antwrp.gsfc.nasa.gov/apod/ap060909.html ]. Above, the principal stars of Leo [ http://www.coldwater.k12.mi.us/lms/planetarium/myth/ leo.html ] are highlighted, while at the far right lies another celestial wanderer that stays close to the ecliptic - Saturn [ http://www.lpod.org/?m=20070305 ]. |
|
Enceladus Creates Saturn's E
…
| Title |
Enceladus Creates Saturn's E Ring |
| Explanation |
The active moon Enceladus appears to be making Saturn's E ring. An amazing picture [ http://ciclops.org/view.php?id=2231 ] showing the moon at work was taken late last year by the Saturn-orbiting Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/ ] and is shown above [ http://photojournal.jpl.nasa.gov/catalog/PIA08321 ]. Enceladus [ http://en.wikipedia.org/wiki/Enceladus_%28moon%29 ] is the dark spot inside the bright flare, right near the center of Saturn's E ring [ http://en.wikipedia.org/wiki/Rings_of_Saturn#E_Ring ]. Streams of ice and water vapor can be seen pouring off Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] into the E ring. The above bright image of the normally faint E-ring [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006Sci...311.1416S ] was made possible by aligning Cassini so that Saturn blocked [ http://antwrp.gsfc.nasa.gov/apod/ap061016.html ] the Sun. From that perspective, small ring particles reflect incoming sunlight [ http://antwrp.gsfc.nasa.gov/apod/ap011030.html ] more efficiently. Cassini has now been orbiting Saturn for almost three years, and is scheduled to swoop [ http://planetary.org/explore/topics/cassini_huygens/tour.html ] by the unexpectedly cryovolcanic [ http://en.wikipedia.org/wiki/Cryovolcano ] Enceladus at least several more times. |
|
Eclipsing the Rings
| Title |
Eclipsing the Rings |
| Explanation |
The March 3rd total lunar eclipse [ http://spaceweather.com/eclipses/gallery_03mar07_page7.htm ] was widely viewed by denizens of planet Earth. But only a day before, well placed observers could also watch [ http://antwrp.gsfc.nasa.gov/apod/ap070309.html ] a lunar occultation of Saturn as the planet passed behind the nearly Full Moon. From Selsey, UK, astronomer Pete Lawrence actually saw Saturn graze the lunar limb, the Moon's bright surface dramatically eclipsing [ http://www.lpod.org/?m=20070305 ] a substantial part of the gas giant's spectacular [ http://antwrp.gsfc.nasa.gov/apod/ap070306.html ] rings. In this summary [ http://www.digitalsky.org.uk/occultations/ 20070302_occultation-summary.jpg ] view of the grazing occultation [ http://en.wikipedia.org/wiki/Grazing_lunar_occultation ], south is up and Saturn's position is shown every 90 seconds in a composite of images constructed from video frames. The frames were all recorded near the occultation event [ http://www.lunar-occultations.com/iota/iotandx.htm ], then combined and adjusted to compensate for the large difference in brightness between Saturn and the lunar surface [ http://www.flickr.com/photos/ltvt/411691250/ ]. |
|
New Horizons at Io
| Title |
New Horizons at Io |
| Explanation |
Spewed from a volcano [ http://volcano.und.edu/volcanoes.html ], a complex plume rises over 300 kilometers above the horizon of Jupiter's moon Io in this image from cameras onboard the New Horizons [ http://pluto.jhuapl.edu/index.php ] spacecraft. The volcano, Tvashtar [ http://www.planetaryexploration.net/jupiter/io/ lava_fountains.html ], is marked by the bright glow [ http://antwrp.gsfc.nasa.gov/apod/ap000606.html ] (about 1 o'clock) at the moon's edge, beyond the terminator or night/day shadow line. The shadow of Io cuts across the plume itself. Also capturing stunning details on the dayside surface, the high resolution image [ http://pluto.jhuapl.edu/gallery/missionPhotos/pages/ 031307.html ] was recorded when the spacecraft was 2.3 million kilometers from Io. Later it was combined with lower resolution color data [ http://pluto.jhuapl.edu/gallery/missionPhotos/pages/ 032807.html ] by astro-imager Sean Walker to produce this sharp portrait of the solar system's most active moon [ http://www.nineplanets.org/io.html ]. Outward bound at almost 23 kilometers "per second", the New Horizons spacecraft should cross the orbit of Saturn in June next year, and is ultimately destined [ http://pluto.jhuapl.edu/mission/passingplanets/ passingPlanets_current.php ] to encounter Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap060624.html ] in 2015. |
|
Nashville Four Planet Skylin
…
| Title |
Nashville Four Planet Skyline |
| Explanation |
So far this February, evening skies [ http://antwrp.gsfc.nasa.gov/apod/ap000504.html ] have been blessed with a glorious Moon and three bright planets, Venus [ http://www.library.utoronto.ca/utel/rp/poems/ longfe10.html ], Jupiter, and Saturn. But just last week, on January 30th, an extreme wide-angle lens allowed astrophotographer Larry Koehn to capture this twilight view of Moon and four planets above [ http://www.seds.org/nineplanets/nineplanets/ see.html ] Nashville, Tennessee, USA. These major solar system [ http://space.jpl.nasa.gov/ ] bodies lie along the ecliptic plane [ http://antwrp.gsfc.nasa.gov/apod/ap001014.html ] and so follow a diagonal line through the picture. Starting near the upper left corner is bright Jupiter [ http://starchild.gsfc.nasa.gov/docs/StarChild/ solar_system_level2/jupiter.html ], which takes on a slightly triangular shape due to the lens distortion. Just below and right of Jupiter is Saturn [ http://www.jpl.nasa.gov/cassini/english/kids/ saturn_in_sky.html ]. Continuing along the diagonal toward the lower right is an overexposed, six day old Moon [ http://www.inconstantmoon.com/ ] and brilliant Venus seemingly embedded in clouds. The fourth planet pictured is Mercury. Notoriously hard to see from planet Earth because it never wanders far from the Sun, Mercury is [ http://antwrp.gsfc.nasa.gov/apod/ap991111.html ] visible just above the lower right corner. The line from Jupiter to Mercury spans about 92 degrees across the Nashville sky. |
|
Liquid Sea on Saturn's Titan
| Title |
Liquid Sea on Saturn's Titan |
| Explanation |
What is this vast dark region on Titan? Quite possible a sea of liquid hydrocarbons [ http://en.wikipedia.org/wiki/Hydrocarbon ]. The region was imaged earlier this month when the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini_spacecraft ] swooped past Saturn's cloudy moon and illuminated part of it with radar. The dark region in the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA09211 ] reflected little radar, an effect expected were the dark surface [ http://antwrp.gsfc.nasa.gov/apod/ap070207.html ] relatively flat, as expected for a liquid. Other indications that the vast dark area is liquid include the coastline-like topology [ http://antwrp.gsfc.nasa.gov/apod/ap050124.html ] of the brighter regions, which appear to include islands, inlets [ http://antwrp.gsfc.nasa.gov/apod/ap971108.html ], and tributary channels. The uninterrupted smoothness of much of the dark sea may indicate that the sea runs deep, with speculation [ http://photojournal.jpl.nasa.gov/catalog/PIA09211 ] holding a depth estimate of tens of meters. A hydrocarbon sea [ http://photojournal.jpl.nasa.gov/catalog/PIA08930 ] on Titan [ http://en.wikipedia.org/wiki/Titan_%28moon%29 ] holds particular interest for exobiologists [ http://exobiology.nasa.gov/ssx/exobiology.html ] as it might be a place where life could develop. In 2005 the Huygens probe landed on Titan and returned the first surface image [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ]s. Cassini will continue to explore Titan, as 13 more flybys [ http://saturn.jpl.nasa.gov/operations/saturn-tour.cfm ] are planned. |
|
Looking Back at an Eclipsed
…
| Title |
Looking Back at an Eclipsed Earth |
| Explanation |
Here is what the Earth looks like during a solar eclipse [ http://www.mreclipse.com/Special/SEprimer.html ]. The shadow of the Moon [ http://antwrp.gsfc.nasa.gov/apod/ap040829.html ] can be seen darkening part of Earth. This shadow [ http://antwrp.gsfc.nasa.gov/apod/ap031127.html ] moved across the Earth [ http://antwrp.gsfc.nasa.gov/apod/earth.html ] at nearly 2000 kilometers per hour. Only observers near the center of the dark circle [ http://antwrp.gsfc.nasa.gov/apod/ap031208.html ] see a total solar eclipse - others see a partial eclipse where only part of the Sun appears blocked by the Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010408.html ]. This spectacular picture [ http://theastropages.com/articles/articles011.htm ] of the 1999 August 11 solar eclipse [ http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html ] was one of the last ever taken from the Mir [ http://antwrp.gsfc.nasa.gov/apod/ap040327.html ] space station. The two bright spots that appear on the upper left are possibly Jupiter and Saturn [ http://theastropages.com/articles/articles011.htm ], although this has yet to be proven. Mir was deorbited [ http://antwrp.gsfc.nasa.gov/apod/ap010323.html ] in a controlled re-entry in 2001. |
|
The Moon's Saturn
| Title |
The Moon's Saturn |
| Explanation |
On May 22nd, just days after sharing the western evening sky with Venus [ http://antwrp.gsfc.nasa.gov/apod/ap070523.html ], the Moon moved on to Saturn [ http://saturn.jpl.nasa.gov/home/index.cfm ] - actually passing in front of the ringed planet when viewed in skies over Europe, northern Africa, and western Asia. Because the Moon and bright planets wander through the sky near the ecliptic plane [ http://antwrp.gsfc.nasa.gov/apod/ap050503.html ], such occultation events [ http://www.lunar-occultations.com/iota/planets/ planets.htm ] are not uncommon, but they are dramatic [ http://antwrp.gsfc.nasa.gov/apod/ap030724.html ], especially in telescopic views. For example, in this sharp image Saturn is captured emerging from [ http://www.tamanti.it/Solar%20Sys/SaturnOccultation.htm ] behind the Moon, giving the illusion that it lies just beyond the Moon's bright edge. Of course, the Moon is a mere 400 thousand kilometers away, compared to Saturn's distance of 1.4 billion [ http://kokogiak.com/megapenny/nine.asp ] kilometers. Taken with [ http://www.kopfgeist.com/besonderes.htm ] a digital camera and 20 inch diameter telescope at the Weikersheim Observatory [ http://www.sternwarte-weikersheim.de/about/ about_set.html ] in southern Germany, the picture is a single exposure adjusted to reduce the difference in brightness between Saturn and the cratered lunar surface. |
|
Red, White, and Blue Sky
| Title |
Red, White, and Blue Sky |
| Explanation |
Contrasting colors in this beautiful sunset sky [ http://www.schursastrophotography.com/10dastro/ vensat070107.html ] were captured on June 30 from Clear Creek Canyon Observatory in central Arizona, USA. The twilight scene includes brilliant [ http://www.digitalsky.org.uk/venus/ shadow-of-venus.html ] Venus as the evening star [ http://www.johnpratt.com/items/astronomy/eve_morn.html ], with a bright Saturn just above it, shining through thin clouds. The two wandering [ http://antwrp.gsfc.nasa.gov/apod/ap070407.html ] planets [ http://antwrp.gsfc.nasa.gov/apod/ap010601.html ] were a mere 1 degree apart or so, about twice the width of the full Moon rising above the eastern horizon on the other side of the sky. In fact, such serene skyviews [ http://www.spaceweather.com/ ] were possible from all over planet Earth as Venus and Saturn approached a conjunction [ http://en.wikipedia.org/wiki/Astronomical_conjunction# Conjunctions_of_planets_in_right_ascension_2005-2020 ]. Regulus, alpha star of the constellation Leo [ http://en.wikipedia.org/wiki/Leo_(constellation) ], is above and to the left of the close planetary pairing. At dusk, lights in tonight's sky will also feature Venus and Saturn low in the west and separated by about 2 degrees. |
|
Saturn The Giant
| Title |
Saturn The Giant |
| Explanation |
Forty years ago today (May 25, 1961) U.S. president John Kennedy announced [ http://history.nasa.gov/moondec.html ] the goal of landing Americans on the Moon by the end of the decade. Kennedy's ambitious speech triggered [ http://www.wamu.org/special/moon.html ] a nearly unprecedented peacetime technological mobilization and one result was the Saturn V [ http://www.hrw.com/science/si-science/earth/spacetravel/ spacerace/SpaceRace/sec300/sec380.html ] moon rocket [ http://kids.msfc.nasa.gov/Rockets/ ]. Its development directed by rocket pioneer Wernher Von Braun, the three stage Saturn V stood [ http://www.hq.nasa.gov/office/pao/History/SP-350/ch-3-1.html ] over 36 stories tall. It had a cluster of five first stage [ http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-000559.html ] engines fueled by [ http://users.commkey.net/Braeunig/space/propel.htm ] liquid oxygen and kerosene which together were capable of producing 7.5 million pounds of thrust. Giant Saturn V rockets ultimately hurled [ http://www.hq.nasa.gov/office/pao/History/SP-4204/ contents.html ] nine Apollo missions [ http://history.nasa.gov/apollo.html ] to the Moon and back again [ http://www.literature.org/authors/verne-jules/ round-the-moon/ ] with six landing on the lunar surface [ http://www.hq.nasa.gov/office/pao/History/alsj/ ]. The first landing, by Apollo 11 [ http://history.nasa.gov/ap11ann/ introduction.htm ], occurred on July 20, 1969 achieving Kennedy's goal. Bathed in light, this Saturn V [ http://www.apollosaturn.com/frame-sv.htm ] awaits an April 11, 1970 launch on the third lunar landing mission, Apollo 13 [ http://antwrp.gsfc.nasa.gov/apod/ap010519.html ]. |
|
Planets over Pony Express La
…
| Title |
Planets over Pony Express Lake |
| Explanation |
Beautiful sunset sky colors [ http://webexhibits.org/causesofcolor/14B.html ] are reflected in Pony Express [ http://www.ponyexpress.org/history.htm ] Lake in this twilight skyview [ http://www.pbase.com/missouri_skies/image/82364390 ] from northern Missouri, USA, planet Earth. Recorded on Monday, a two day old crescent Moon and brilliant planet Venus shine through thin clouds. Joining the conjunction [ http://antwrp.gsfc.nasa.gov/apod/ap070704.html ] on the right of the Moon's sunlit crescent is fellow wanderer [ http://www.nasm.si.edu/ceps/etp/discovery/ disc_ancient.html ] Saturn, with Regulus, alpha star of the constellation Leo, above and right of Venus. Moonlight and Venus light [ http://www.digitalsky.org.uk/venus/shadow-of-venus.html ] streak the almost-calm lake waters. |
|
Unusual Cratering on Saturn'
…
| Title |
Unusual Cratering on Saturn's Dione |
| Explanation |
Why does one half of Dione have more craters than the other? Start with the fact that Saturn [ http://en.wikipedia.org/wiki/Saturn ]'s moon Dione always has one side that faces Saturn, and always has one side that faces away. This is similar to Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap051113.html ]. This tidal locking [ http://en.wikipedia.org/wiki/Tidal_locking ] means that one side of Dione [ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Dione ] always leads as the moon progresses in its orbit, while the other side always trails. Dione [ http://en.wikipedia.org/wiki/Dione_%28moon%29 ] should therefore have undergone a significant amount of impacts on its leading half. But the current leading half of Dione [ http://antwrp.gsfc.nasa.gov/apod/ap060905.html ] is less cratered than the trailing half! A possible explanation is that some impacts were so large they spun Dione [ http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2034.pdf ], sometimes changing the part that suffered the highest impact rate before the moon's spin again became locked. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08956 ], it is the top part of Dione that appears significantly more cratered than the bottom half. |
|
Solar System Web Cam
| Title |
Solar System Web Cam |
| Explanation |
Ranging throughout the solar system [ http://space.jpl.nasa.gov/ ], these pictures all have something in common. They were taken with an 8 inch diameter telescope, a size popular with amateur astronomy buffs, and slightly modified "web cam" of the type widely used to send images out over the internet. The results are clearly remarkable for [ http://www.djcash.demon.co.uk/astro/webcam/webcam.htm ] such inexpensive and readily available equipment. Each sharp image was produced from 20 to 30 frames which were digitally stacked and processed using free software [ http://utopia.ision.nl/users/rjstek/english/software/ index.htm ]. Until recently, digital imaging for amateur astronomers required a specialized camera [ http://www.wvi.com/~rberry/cookbook.htm ], but the advent of low-light video surveillance cameras and web cams now presents other options for relatively bright [ http://www.astrabio.demon.co.uk/QCUIAG/ac/3dmoon.htm ] solar system objects. Want to try some unconventional [ http://www.astrabio.demon.co.uk/QCUIAG/ ] web cam astronomy? Geoff Chester, Public Affairs Officer at the U.S. Naval Observatory [ http://www.usno.navy.mil ], offers these images and an account of his own adventures [ http://www.usno.navy.mil/pao/QuickCamAstro.shtml ] from a suburban front lawn near Washington D.C. |
|
Iapetus: 3D Equatorial Ridge
| Title |
Iapetus: 3D Equatorial Ridge |
| Explanation |
This bizarre, equatorial ridge extending across and beyond the dark, leading hemisphere of Iapetus [ http://www.nineplanets.org/iapetus.html ] gives the two-toned [ http://antwrp.gsfc.nasa.gov/apod/ap070914.html ] Saturnian [ http://en.wikipedia.org/wiki/ Saturn%27s_moons_in_fiction#Iapetus ] moon a distinct walnut shape. With red/blue [ http://photojournal.jpl.nasa.gov/Help/ VendorList.html#Glasses ] glasses you can check out a remarkable stereo composition of this extraordinary feature -- based on close-up images from this week's Cassini spacecraft flyby [ http://hownow.brownpau.com/archives/2007/09/ iapetus_flyover_gif/ ]. In fact, the ridge's combination of equatorial symmetry and scale, about 20 kilometers wide and reaching up to 20 kilometers above the surface, is not known to be duplicated anywhere else in our solar system. The unique feature was discovered in [ http://saturn.jpl.nasa.gov/multimedia/images/ image-details.cfm?imageID=1270 ] Cassini images from 2004. It appears to be heavily cratered and therefore ancient, but the origin of the equatorial ridge [ http://en.wikipedia.org/wiki/ Iapetus_%28moon%29#The_equatorial_ridge ] on Iapetus [ http://en.wikipedia.org/wiki/ 2001:_A_Space_Odyssey_(novel)#Differences_with_the_film ] remains a mystery. |
|
4,000 Kilometers Above Satur
…
| Title |
4,000 Kilometers Above Saturn's Iapetus |
| Explanation |
What does the surface of Saturn's mysterious moon Iapetus look like? To help find out, the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini_spacecraft ] now orbiting Saturn [ http://www.nineplanets.org/saturn.html ] was sent soaring last week just 2,000 kilometers from the unique equatorial ridge of the unusual walnut-shaped [ http://antwrp.gsfc.nasa.gov/apod/ap050201.html ] two-toned moon [ http://antwrp.gsfc.nasa.gov/apod/ap060103.html ]. The above image [ http://antwrp.gsfc.nasa.gov/apod/ap070919.html http://photojournal.jpl.nasa.gov/catalog/PIA08372 ] from Cassini is from about 4,000 kilometers out and allows objects under 100-meters across to be resolved. Cassini found an ancient and battered landscape [ http://antwrp.gsfc.nasa.gov/apod/ap051213.html ] of craters, sloping hills, and mountains as high as 10 kilometers and so rival [ http://en.wikipedia.org/wiki/Everest ] the 8.8-kilometer height of Mt. Everest [ http://antwrp.gsfc.nasa.gov/apod/ap070408.html ] on Earth. Just above the center of this image [ http://photojournal.jpl.nasa.gov/catalog/PIA08372 ] is a small bright patch where an impacting rock might have uncovered deep clean water ice. Space scientists [ http://www.aas.org/dps/ ] will be studying flyby images like this for clues to the origin of Iapetus' unusual shape [ http://antwrp.gsfc.nasa.gov/apod/ap070915.html ] and coloring [ http://antwrp.gsfc.nasa.gov/apod/ap070914.html ] with particular emphasis because no more close flybys [ http://saturn.jpl.nasa.gov/news/events/iapetus/index.cfm ] of the enigmatic world are planned. APOD editor to review best space pictures in Philadelphia next Wednesday [ http://www.rittenhouseastronomicalsociety.org/ ] |
|
Iapetus in Black and White
| Title |
Iapetus in Black and White |
| Explanation |
Iapetus, Saturn's [ http://saturn.jpl.nasa.gov/science/moons/ moonDetails.cfm?pageID=7 ] third largest moon, is a candidate for the strangest moon of Saturn. Tidally locked [ http://en.wikipedia.org/wiki/Tidal_locking ] in its orbit around the ringed gas giant, Iapetus is sometimes called the yin-yang moon [ http://www.planetary.org/news/2007/ 0906_Cassini_Zeroes_in_on_Saturns_YinYang.html ] because [ http://en.wikipedia.org/wiki/Image:Yin_yang.svg ] its leading hemisphere is very dark, reflecting about 5 percent of the Sun's light, while its trailing hemisphere is almost as bright as snow. This recent Cassini [ http://www.nasa.gov/mission_pages/cassini/media/ cassini20070912.html ] spacecraft flyby image [ http://photojournal.jpl.nasa.gov/catalog/PIA08374 ] is one of the closest views ever. It spans about 35 kilometers across a cratered transition [ http://www.planetary.org/blog/article/00001130/ ] zone between bright and dark terrain. Iapetus itself has a density close to that of water ice, but the detailed reflective properties of the dark material suggest an organic composition. Honoring the moon's discoverer, the dark terrain is called Cassini [ http://messier.obspm.fr/xtra/Bios/cassini.html ] Regio. |
|
The Great Basin on Saturn's
…
| Title |
The Great Basin on Saturn's Tethys |
| Explanation |
Some moons wouldn't survive the collision. Tethys [ http://en.wikipedia.org/wiki/Tethys_%28moon%29 ], one of Saturn's larger moons [ http://www.nineplanets.org/saturn.html ] at about 1000 kilometers in diameter, survived the collision, but sports today the expansive impact crater [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] Odysseus. Sometimes called the Great Basin [ http://antwrp.gsfc.nasa.gov/apod/ap060208.html ], Odysseus [ http://en.wikipedia.org/wiki/Odysseus_%28crater%29 ] occurs on the leading hemisphere of Tethys [ http://en.wikipedia.org/wiki/Tethys_%28mythology%29 ] and shows its great age by the relative amount of smaller craters that occur inside its towering walls [ http://antwrp.gsfc.nasa.gov/apod/ap050315.html ]. Another large crater, Melanthius [ http://en.wikipedia.org/wiki/Melanthius ], is visible near the moon's terminator [ http://antwrp.gsfc.nasa.gov/apod/ap050611.html ]. The density of Tethys is similar to water-ice [ http://www.lsbu.ac.uk/water/phase.html ]. The above digitally enhanced image [ http://photojournal.jpl.nasa.gov/catalog/PIA09017 ] was captured in July by the robot Cassini spacecraft [ http://saturn.jpl.nasa.gov/operations/index.cfm ] in orbit around Saturn as it swooped past the giant ice ball [ http://www.chemistry.org/portal/a/c/s/1/feature_tea.html?DOC=teachers%5Ctea_megacryometeors.html ]. |
|
The 47 Ursae Majoris System
| Title |
The 47 Ursae Majoris System |
| Explanation |
Watching and waiting [ http://exoplanets.org/ ], astronomers have uncovered the presence of more than 70 planets orbiting stars other than the Sun. So far almost all these extrasolar planets [ http://cfa-www.harvard.edu/planets/ ] have crazy elongated orbits, lie uncomfortably close to their parent stars, or are found in bizarre, inhospitable systems. Yet a reported new planet [ http://www.nsf.gov/od/lpa/news/press/01/ pr0164.htm ] discovery indicates for the first time that a nearby sun-like star, 47 Ursae Majoris (47 UMa), has at least two planets in nearly circular orbits more reminiscent of Jupiter [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ jupiterfact.html ] and Saturn [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ saturnfact.html ] in our own familiar Solar System [ http://www.jpl.nasa.gov/basics/bsf1-1.html ]. The planets are too distant and faint to be photographed directly. Still, 13 years of [ http://exoplanets.org/esp/47uma/47uma.shtml ] spectroscopic observations of 47 UMa have revealed the wobbling [ http://exoplanets.org/doppler.html ] signature of a second planet intertwined with [ http://exoplanets.org/esp/47uma/47uma.shtml ] one previously known. In this artist's illustration [ http://extrasolar.spaceart.org/extrasol.html ], the worlds of 47 UMa [ http://antwrp.gsfc.nasa.gov/apod/ap971005.html ] hang over the rugged volcanic landscape of a hypothetical moon. The moon orbits the newly discovered planet [ http://exoplanets.org/esp/47uma/47uma_announce.html ], imagined here with Saturn-like rings, while the previously known planet is visible as a tiny crescent, close to the yellowish star. Closer still to 47 UMa is another tiny dot, a hypothetical [ http://www.fourmilab.to/terranova/ terranova.html ] Earth-like water world [ http://antwrp.gsfc.nasa.gov/apod/ap980530.html ]. About 51 light-years distant, 47 UMa can be found in planet Earth's sky near the Big Dipper [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Ursa_Major.html ]. |
|
Enceladus Ice Geysers
| Title |
Enceladus Ice Geysers |
| Explanation |
Ice geysers erupt on Enceladus [ http://en.wikipedia.org/wiki/Enceladus_%28moon%29 ], bright and shiny inner moon of Saturn. Shown in this false-color image [ http://photojournal.jpl.nasa.gov/catalog/PIA08386 ], a backlit view of the moon's southern limb, the majestic, icy plumes were discovered by [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] instruments on the Cassini Spacecraft during close encounters with Enceladus in November of 2005. Eight source locations [ http://saturn.jpl.nasa.gov/news/ press-release-details.cfm?newsID=780 ] for these geysers have now been identified along substantial surface fractures [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ] in the moon's south polar region. Researchers suspect the geysers arise [ http://photojournal.jpl.nasa.gov/catalog/PIA07799 ] from near-surface pockets of liquid water with temperatures [ http://lamar.colostate.edu/~hillger/temps.htm ] near 273 kelvins (0 degrees C). That's hot when compared to the distant moon's surface temperature of 73 kelvins (-200 degrees C). The cryovolcanism [ http://en.wikipedia.org/wiki/Cryovolcanism ] is a dramatic sign that tiny, 500km-diameter Enceladus is surprisingly [ http://saturn.jpl.nasa.gov/news/ press-release-details.cfm?newsID=662 ] active. Enceladus ice geysers also likely produce Saturn's faint but extended E ring [ http://www.planetary.org/saturn/rings.html ]. |
|
Bright Planets, Crescent Moo
…
| Title |
Bright Planets, Crescent Moon |
| Explanation |
Early risers are currently enjoying the sight [ http://stardate.org/nightsky/planets/ ] of dazzling Venus [ http://www.nineplanets.org/venus.html ], near the eastern horizon as the morning star [ http://www.windows.ucar.edu/tour/link=/venus/ morning_star.html&edu=high ]. Recorded on October 7, this predawn skyview [ http://www.usno.navy.mil/pao/sky/sky_week.shtml ] does feature Venus at the upper right. It also includes a crescent Moon and Saturn (lower left). In fact, holding your fist at arms length would have easily covered [ http://chandra.harvard.edu/photo/scale.html ] both planets and the Moon in this 5 degree wide field. Earthshine [ http://antwrp.gsfc.nasa.gov/apod/ap020419.html ], sunlight reflected from planet Earth's dayside, illuminates features on the lunar nightside. A close inspection of Saturn itself reveals a nearby pinpoint of light corresponding to Saturn's [ http://saturn.jpl.nasa.gov/science/moons/index.cfm ] large moon Titan. Though the Moon has moved on, the tight triangle [ http://www.spaceweather.com/images2007/12oct07/ skymap_north.gif ] formed by Venus, Saturn, and Regulus (top), alpha star in the constellation Leo, will continue to look impressive in early morning skies over the next few days. Early bird astrophotographer Jay Ouellet also described Mars as [ http://www.spaceweather.com/images2007/11oct07/ skymap_north_mars.gif ] a "brilliant red diode" in his dark country sky east of Quebec City, Canada. Count the Stars: The Great World Wide Star Count [ http://www.windows.ucar.edu/citizen_science/starcount/ ] |
|
The Strange Trailing Side of
…
| Title |
The Strange Trailing Side of Saturn's Iapetus |
| Explanation |
What has happened to Saturn's moon Iapetus? Vast sections of this strange world [ http://en.wikipedia.org/wiki/Iapetus_%28moon%29 ] are dark as coal [ http://en.wikipedia.org/wiki/Coal ], while others are as bright as ice. The composition of the dark material is unknown, but infrared [ http://science.hq.nasa.gov/kids/imagers/ems/infrared.html ] spectra [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] indicate that it possibly contains some dark form of carbon [ http://periodic.lanl.gov/elements/6.html ]. Iapetus also has an unusual equatorial ridge [ http://antwrp.gsfc.nasa.gov/apod/ap050201.html ] that makes it appear like a walnut [ http://www.whfoods.com/genpage.php?tname=foodspice&dbid=99 ]. To help better understand this mysterious moon, NASA [ http://www.nasa.gov/about/highlights/index.html ] directed the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini_spacecraft ] orbiting Saturn to swoop within 2,000 kilometers [ http://antwrp.gsfc.nasa.gov/apod/ap070919.html ] just last month. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08384 ], from about 75,000 kilometers out, Cassini's trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is always trailing [ http://en.wikipedia.org/wiki/Tidal_locking ]. A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an older crater [ http://antwrp.gsfc.nasa.gov/apod/ap060530.html ] of similar size. The dark material [ http://antwrp.gsfc.nasa.gov/apod/ap070914.html ] is seen increasingly coating the easternmost part of Iapetus [ http://antwrp.gsfc.nasa.gov/apod/ap060103.html ], darkening craters and highlands alike. Close inspection [ http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ ] indicates that the dark coating typically faces the moon's equator. Whether Iapetus' colors are the result of unusual [ http://antwrp.gsfc.nasa.gov/apod/ap061114.html ] episodes of internal volcanism [ http://antwrp.gsfc.nasa.gov/apod/ap051002.html ] or external splattering [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] remains unknown. This and other images from Cassini's Iapetus flyby [ http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1270 ] are being studied for even greater clues. |
|
Moon Occults Saturn
| Title |
Moon Occults Saturn |
| Explanation |
On September 18, 1997, many stargazers in the U. S. [ http://antwrp.gsfc.nasa.gov/apod/ap000708.html ] were able to watch a lovely early morning lunar occultation [ http://www.skypub.com/sights/occultations/occultations.shtml ] as a bright Moon [ http://jrscience.wcp.muohio.edu/lab/MoonLab.html ] passed in front of Saturn. Using a 1.2 meter reflector [ http://cfa-www.harvard.edu/cfa/oir/FLWO/FLWO/48/48.html ], astronomer Kris Stanek had an excellent view of this [ http://cfa-www.harvard.edu/~kstanek/Saturn/ ] dream-like event from the Whipple Observatory [ http://linmax.sao.arizona.edu/help/FLWO/whipple.html ] atop Arizona's Mount Hopkins [ http://cfa-www.harvard.edu/flwo/visitcenter.html ]. This animated gif image was constructed by Wes Colley from 4 frames taken by Stanek at 35 second intervals as the ringed planet emerged from behind the Moon's [ http://antwrp.gsfc.nasa.gov/apod/ap970916.html ] dark limb. While lunar occultations [ http://www.skypub.com/sights/occultations/lunar/ 0101lunarocc.html ] of fairly bright stars and planets are not extremely rare events, their exact timing [ http://www.lunar-occultations.com/iota/iotandx.htm ] depends critically on the observer's location. For observers in western North America [ http://www.lunar-occultations.com/iota/0910sat.htm ], the Moon will next occult Saturn on Monday morning, September 10 [ http://www.lunar-occultations.com/iota/0910sat.htm ]. |
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