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Images of Uranus and Goddard Space Flight Center (GSFC)
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Lightning on Earth
| Title |
Lightning on Earth |
| Explanation |
Nobody knows what causes lightning. It is known that charges [ http://physics.bu.edu/~duffy/PY106/Charge.html ] slowly separate in some clouds [ http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml ] causing rapid electrical discharges [ http://www.eng.tau.ac.il/Pages/Departments/Inter/edp_lab/ ] (lightning), but how electrical charges [ http://physicsstudio.indstate.edu/java/potential/ProyectI.html ] get separated in clouds [ http://www.geo.mtu.edu/department/classes/ge406/tjbrabec/cloud.html ] remains a topic of much research. Nevertheless, lightning [ http://wvlightning.com/info.html ] bolts are common in clouds during rainstorms, and on average 6000 lightning bolts occur between clouds and the Earth every minute. Above [ http://www.noao.edu/image_gallery/html/im0426.html ], several lightning strokes were photographed behind Kitt Peak National Observatory [ http://www.noao.edu/outreach/kpoutreach.html ] in Arizona [ http://www.state.az.us/ ]. Lightning [ http://bondo.wsc.mass.edu/dept/garp/faculty/lightn.htm ] has also been found on the planets Venus [ http://www.lpl.arizona.edu/~hansell/lightning/poster.html ], Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap971216.html ], Saturn [ http://learn.jpl.nasa.gov/projectspacef/bkg130b.html ], and Uranus [ http://www.spacetoday.org/SolSys/Uranus/Uranus.html ]. NASA [ http://www.nasa.gov/ ] launched the TRMM mission [ http://trmm.gsfc.nasa.gov/news.html ] in 1997 that continues to measure rainfall and lightning [ http://thunder.msfc.nasa.gov/primer/ ] on planet Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ]. |
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Eight Planets and New Solar
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| Title |
Eight Planets and New Solar System Designations |
| Explanation |
How many planets are in the Solar System? This popular question now has a new formal answer according the International Astronomical Union [ http://en.wikipedia.org/wiki/International_Astronomical_Union ] (IAU): eight. Last week, the IAU voted [ http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html ] on a new definition for planet [ http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html ] and Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap010319.html ] did not make the cut. Rather, Pluto was re-classified as a dwarf planet [ http://en.wikipedia.org/wiki/Dwarf_planet ] and is considered as a prototype for a new category of trans-Neptunian objects [ http://en.wikipedia.org/wiki/Trans-Neptunian_object ]. The eight planets now recognized by the IAU are: Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap040912.html ], Venus [ http://antwrp.gsfc.nasa.gov/apod/ap040516.html ], Earth [ http://antwrp.gsfc.nasa.gov/apod/ap050102.html ], Mars [ http://antwrp.gsfc.nasa.gov/apod/ap060730.html ], Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap050911.html ], Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap041225.html ], Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap010826.html ], and Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap010821.html ]. Solar System objects now classified as dwarf planets are: Ceres [ http://antwrp.gsfc.nasa.gov/apod/ap060821.html ], Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap060624.html ], and the currently unnamed 2003 UB313 [ http://antwrp.gsfc.nasa.gov/apod/ap060207.html ]. Planets, by the new IAU definition, must be in orbit around the sun, be nearly spherical, and must have cleared the neighborhood around their orbits. The demotion of Pluto [ http://www.nineplanets.org/pluto.html ] to dwarf planet status is a source of continuing dissent [ http://www.badastronomy.com/bablog/2006/08/18/colbert-takes-neil-tyson-down/ ] and controversy [ http://newswire.ascribe.org/cgi-bin/behold.pl?ascribeid=20060818.063045&time=07%2006%20PDT&year=2006&public=0 ] in the astronomical community. |
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Titania's Trenches
| Title |
Titania's Trenches |
| Explanation |
British astronomer Sir William Herschel [ http://star.arm.ac.uk/history/herschel.html ] discovered Titania and Oberon in January of 1787. He wasn't reading Shakespeare's [ http://the-tech.mit.edu/Shakespeare/works.html ]"A Midsummer Night's Dream" though, he was making the first telescopic observations of moons of the planet Uranus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/uranus.html ] (a planet which he himself discovered in 1781 [ http://www-groups.dcs.st-and.ac.uk/~history/ HistTopics/Neptune_and_Pluto.html ]). In January of 1986, nearly 200 years later, NASA's robot explorer Voyager 2 became the only spacecraft to visit the remote Uranian [ http://antwrp.gsfc.nasa.gov/apod/ap990531.html ] system [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ]. Above is Voyager's highest resolution picture of Titania [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00039 ], Uranus' largest moon. The picture is a composite of two images recorded from a distance of 229,000 miles. The icy, rocky world [ http://antwrp.gsfc.nasa.gov/apod/ap960304.html ] is seen to be covered with impact craters. A prominent system of fault valleys, some nearly 1,000 miles long, is visible as trench-like features near the terminator (shadow line). Deposits of highly reflective material which may represent frost can be seen along the sun-facing valley walls. The large impact crater near the top, known as Gertrude [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/uranus/titacrat.html ], is about 180 miles across. At the bottom the 60 mile wide fault valley, Belmont Chasma [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/uranus/titachas.html ], cuts into crater Ursula. Titania itself [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/wall/titania.html ] is 1,000 miles in diameter. |
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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, |
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Steep Cliffs on Mars
| Title |
Steep Cliffs on Mars |
| Explanation |
Vertical cliffs of nearly two kilometers occur near the North Pole of Mars. Also visible in the above image [ http://www.esa.int/SPECIALS/Mars_Express/SEMLF6D3M5E_1.html ] of the Martian North Polar Cap [ http://antwrp.gsfc.nasa.gov/apod/ap021224.html ] are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash [ http://volcanoes.usgs.gov/Products/Pglossary/ash.html ]. The cliffs are thought to border volcanic caldera [ http://antwrp.gsfc.nasa.gov/apod/ap040526.html ]. Although the sheer drop [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ] of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System [ http://www.nineplanets.org/overview.html ], including the 3.4-kilometer depth of Colca Canyon [ http://www.bootsnall.com/articles/02-08/where-is-the-deepest-canyon-in-the-world-arequipa-peru.html ] on Earth and the 20 kilometer depth of Verona Rupes [ http://en.wikipedia.org/wiki/Verona_Rupes ] on Uranus' moon Miranda [ http://astrogeology.usgs.gov/Projects/BrowseTheGeologicSolarSystem/MirandaBack.html ]. The above image [ http://www.esa.int/SPECIALS/Mars_Express/SEMLF6D3M5E_0.html ], digitally reconstructed into a perspective view [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005LPI....36.1769S ], was taken by the High Resolution Stereo Camera [ http://berlinadmin.dlr.de/Missions/express/kamera/kameraeng.shtml ] on board the ESA [ http://www.esa.int/ ]'s robotic Mars Express spacecraft [ http://www.esa.int/esaSC/120379_index_0_m.html ] currently orbiting Mars [ http://www.nineplanets.org/mars.html ]. |
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Verona Rupes: Tallest Known
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| Title |
Verona Rupes: Tallest Known Cliff in the Solar System |
| Explanation |
Could you survive a jump off the tallest cliff in the Solar System? Quite possibly. Verona Rupes [ http://en.wikipedia.org/wiki/Verona_Rupes ] on Uranus [ http://www.nineplanets.org/uranus.html ]' moon Miranda [ http://www.nineplanets.org/miranda.html ] is estimated to be 20 kilometers deep -- ten times the depth of the Earth's Grand Canyon [ http://www.nps.gov/grca/ ]. Given Miranda [ http://en.wikipedia.org/wiki/Miranda_%28moon%29 ]'s low gravity, it would take about 12 minutes for a thrill-seeking adventurer [ http://video.google.com/videoplay?docid=2090669779765584576 ] to fall from the top, reaching the bottom at the speed of a racecar -- about 200 kilometers per hour. Even so, the fall might be survivable given proper airbag [ http://www.howstuffworks.com/airbag.htm ] protection. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA00044 ] of Verona Rupes was captured by the passing Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap020831.html ] 2 robotic spacecraft in 1986. How the giant cliff was created remains unknown, but is possibly related to a large impact [ http://antwrp.gsfc.nasa.gov/apod/ap050308.html ] or tectonic [ http://en.wikipedia.org/wiki/Extensional_tectonics ] surface motion. |
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Uranus: The Tilted Planet
| Title |
Uranus: The Tilted Planet |
| Explanation |
Uranus is the third largest planet in our Solar System [ http://www.nineplanets.org/overview.html ] after Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap010826.html http://www.solarviews.com/eng/saturn.htm ]. Uranus [ http://www.nineplanets.org/uranus.html ] is composed mostly of rock and ices, but with a thick hydrogen [ http://chemlab.pc.maricopa.edu/periodic/h.html ] and helium [ http://antwrp.gsfc.nasa.gov/apod/ap010120.html ] atmosphere. The blue hue of Uranus' atmosphere arises from the small amount of methane [ http://scifun.chem.wisc.edu/chemweek/methane/methane.html ] which preferentially absorbs red light. This picture [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01360 ] was snapped by the Voyager 2 spacecraft [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] in 1986 - the only spacecraft ever to visit Uranus. Uranus [ http://antwrp.gsfc.nasa.gov/apod/uranus.html ] has many moons [ http://antwrp.gsfc.nasa.gov/apod/ap990531.html ] and a ring system [ http://antwrp.gsfc.nasa.gov/apod/ap971126.html ]. Uranus, like Venus [ http://antwrp.gsfc.nasa.gov/apod/venus.html ], has a rotation axis that is greatly tilted and sometimes points near the Sun. It remains an astronomical mystery why Uranus' axis [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1991LPIP...22...59S ] is so tilted. Uranus and Neptune [ http://antwrp.gsfc.nasa.gov/apod/neptune.html ] are quite similar: Uranus is slightly larger but less massive. |
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Jupiter's Rings
| Title |
Jupiter's Rings |
| Explanation |
Astronomers using NASA's Voyager [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] spacecraft to search for a ring system around Jupiter discovered these faint rings in 1979. Unlike Saturn's bright rings which are composed of chunks of rock and ice, Jupiter's rings [ http://ringside.arc.nasa.gov/www/jupiter/jupiter.html ] appear to consist of fine particles of dust. One possibility is that the dust is produced by impacts with Jupiter's inner moons. This false color image has been computer enhanced. The gas giant planets, Jupiter, Saturn, Uranus, and Neptune are all known to have rings. For more information about planetary ring systems see the Planetary Rings Node [ http://ringside.arc.nasa.gov/ ]. Tomorrow's picture: A Volcanic Moon |
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Neptune: Big Blue Giant
| Title |
Neptune: Big Blue Giant |
| Explanation |
This picture was taken by the Voyager 2 [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] spacecraft in 1986 - the only spacecraft ever to visit Neptune. Neptune [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/neptune.html ] will be the farthest planet from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] until 1999, when the elliptical orbit of Pluto will cause it to once again resume this status. Neptune [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/neptune.html ], like Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ], is composed mostly of liquid water, methane and ammonia, is surrounded by a thick gas atmosphere of mostly hydrogen and helium, and has many moons and rings. Neptune [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-neptune.html ]'s moon Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] is unlike any other and has active volcanoes. The nature of Triton [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/triton.html ]'s unusual orbit around Neptune is the focus of much discussion and speculation. Tomorrow's picture: Pluto: The Frozen Planet |
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Venus: Earth's Sister Planet
| Title |
Venus: Earth's Sister Planet |
| Explanation |
This picture in visible light was taken by the Galileo [ http://nssdc.gsfc.nasa.gov/planetary/galileo.html ] spacecraft. Venus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/venus.html ] is very similar to Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ] in size and mass - and so is sometimes referred to as Earth's sister planet - but Venus has a quite different climate. Venus' [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/venus.html ] thick clouds and closeness to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] (only Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap950814.html ] is closer) make it the hottest planet - much hotter than the Earth. Humans could not survive there, and no life of any sort has ever been found. When Venus [ http://nssdc.gsfc.nasa.gov/photo_gallery/PhotoGallery-Venus.html ] is visible it is usually the brightest object in the sky after the Sun and the Moon. More than 20 spacecraft have visited Venus including Venera 9, which landed on the surface, and Magellan [ http://stardust.jpl.nasa.gov/mveg/guide.html ], which used radar to peer through the clouds and make a map of the surface. There are still many things about Venus's unusual atmosphere that astronomers don't understand. Tomorrow's picture: Uranus: The Tilted Planet |
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Uranus' Moon Miranda
| Title |
Uranus' Moon Miranda |
| Explanation |
NASA's robot spacecraft Voyager 2 passed the planet Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] and its moons in 1986. While the cloud tops of Uranus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/uranus.html ] proved to be rather featureless, the surface of Miranda [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/miranda.html ], the innermost of Uranus [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/uranus.html ]' large moons, showed several interesting features. Voyager 2 passed closer to Miranda [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/miranda.html ] than to any Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] body and hence photographed it with the clearest resolution. Miranda's heavily cratered terrain shows grooves like Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] and several valleys and cliffs. Miranda is made of a roughly equal mix of ice and rock. Miranda was discovered by Gerard Kuiper in 1948. |
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Uranus' Moon Ariel: Valley W
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| Title |
Uranus' Moon Ariel: Valley World |
| Explanation |
What formed Ariel [ http://bang.lanl.gov/solarsys/ariel.htm ]'s valleys? This question presented itself when Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 2 passed this satellite of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in January 1986. Speculation [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990Icar%2E%2E%2E87%2E%2E110T&db_key=AST ] includes that heating caused by the ancient tides of Uranus caused moonquakes and massive shifting of the moon's surface. In any event, a huge network of sunken valleys was found to cover this frozen moon, and some unknown material now coats the bottoms of many of these channels. Ariel [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ariel.html ] is the second closest to Uranus outside of Miranda [ http://antwrp.gsfc.nasa.gov/apod/ap951224.html ], and is composed of roughly half water ice and half rock. Ariel was discovered by William Lassell [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/help.html#lassell ] in 1851. |
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Two Hours Before Neptune
| Title |
Two Hours Before Neptune |
| Explanation |
Two hours before closest approach to Neptune [ http://www.nineplanets.org/neptune.html ] in 1989, the Voyager 2 [ http://vraptor.jpl.nasa.gov/voyager/vgrfaqs.html ] robot spacecraft snapped this picture [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-neptune.html ]. Clearly visible for the first time were long light-colored cirrus [ http://www.bham.ac.uk/geography/met/clouds/h1.htm ]-type clouds floating high in Neptune's atmosphere [ http://nssdc.gsfc.nasa.gov/photo_gallery/caption/neptune_clouds.txt ]. Shadows of these clouds can even be seen on lower cloud decks. Most of Neptune's atmosphere [ http://antwrp.gsfc.nasa.gov/apod/ap960507.html ] is made of hydrogen [ http://chemlab.pc.maricopa.edu/periodic/h.html ] and helium [ http://chemlab.pc.maricopa.edu/periodic/He.html ], which is invisible. Neptune's blue color therefore comes from smaller amounts of atmospheric methane [ http://www.epa.gov/ghginfo/ ], which preferentially absorbs red light. Neptune [ http://pds.jpl.nasa.gov/planets/welcome/neptune.htm ] has the fastest winds in the Solar System [ http://www.nineplanets.org/overview.html ], with gusts reaching 2000 kilometers per hour. Speculation [ http://www.berkeley.edu/news/berkeleyan/1999/1006/diamonds.html ] holds that diamonds [ http://www.sdnhm.org/exhibits/diamonds/facts.html ] may be created in the dense hot conditions that exist under the clouds-tops of Uranus [ http://spacelink.msfc.nasa.gov/Instructional.Materials/Curriculum.Support/Space.Science/Our.Solar.System/Uranus/ ] and Neptune. |
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Uranus' Largest Moon: Titani
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| Title |
Uranus' Largest Moon: Titania |
| Explanation |
Titania's tortured terrain is a mix of valleys and craters. NASA's interplanetary robot spacecraft Voyager [ http://spacelink.msfc.nasa.gov/NASA.Projects/Planetary.Probes/Voyager/Mission.Summary ] 2 passed this moon of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in 1986 and took the above photograph. The photograph was then transmitted back to earth by radio [ http://www.science.uwaterloo.ca/physics/p13news/number_2/maxnew-2.html ]. The valleys of Titania [ http://bang.lanl.gov/solarsys/titania.htm ] resemble those on Ariel [ http://antwrp.gsfc.nasa.gov/apod/ap960303.html ] indicate that Titania underwent some unknown tumultuous resurfacing event in its distant past. Although Titania [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/titania.html ] is Uranus' largest moon, it is still much smaller than Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] - the largest moon of Uranus' sister planet Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap950817.html ]. Titania is essentially a large dirty iceball that orbits Uranus - it is composed of about half water-ice and half rock. Titania was discovered by William Hershel [ http://www.dsi.unimi.it/Users/Students/amoroso/sun/fortunes/life-e.html ] in 1787. |
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Uranus's Moon Oberon: Impact
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| Title |
Uranus's Moon Oberon: Impact World |
| Explanation |
Oberon is the most distant and second largest moon of Uranus. Discovered by William Herschel [ http://www.adventure.com/library/encyclopedia/space/herschls.html ] in 1787, the properties of the world remained relatively unknown until the robot spacecraft Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 2 passed it during its flyby of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in January 1986. Compared to Uranus' moons Ariel [ http://antwrp.gsfc.nasa.gov/apod/ap960303.html ], Titania [ http://antwrp.gsfc.nasa.gov/apod/ap960304.html ], and Miranda [ http://antwrp.gsfc.nasa.gov/apod/ap951224.html ], Oberon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/oberon.html ] is heavily cratered, and in this way resembles Umbriel [ http://antwrp.gsfc.nasa.gov/apod/ap960407.html ]. Like all of Uranus' large moons, Oberon [ http://bang.lanl.gov/solarsys/oberon.htm ] is composed of roughly half ice and half rock. Note that Oberon has at least one large mountain, visible on the limb at the lower left, that rises 6 km off the surface. |
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Uranus's Moon Umbriel: A Mys
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| Title |
Uranus's Moon Umbriel: A Mysterious Dark World |
| Explanation |
Why is Umbriel so dark? This dark moon reflects only half the light of other Uranus' [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] moons such as Ariel [ http://antwrp.gsfc.nasa.gov/apod/ap960303.html ]. And what is that bright ring at the top? Unfortunately, nobody yet knows. These questions presented themselves when Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 2 passed this satellite of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] in January 1986. Voyager found an old surface with unusually large craters, and determined Umbriel [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/umbriel.html ]'s composition to be about half ice and half rock. Umbriel [ http://bang.lanl.gov/solarsys/umbriel.htm ] is the fourth largest and third most distant of Uranus' five large moons. Umbriel was discovered in 1851 by William Lassell [ http://www.ast.cam.ac.uk/~naw96/lassell/lassell.htm ]. |
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Uranus' Ring System
| Title |
Uranus' Ring System |
| Explanation |
The rings of Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] are thin, narrow, and dark compared to other planetary ring systems. Brightened artificially by computer, the ring particles reflect as little light as charcoal, although they are really made of ice chucks darkened by rock. This false-color, infrared picture [ http://www.stsci.edu/pubinfo/PR/96/15/A.html ] from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ] taken in July 1995 shows the rings in conjunction to the planet. The infrared [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#infrared ] light allows one to see detail in different layers of Uranus' [ http://antwrp.gsfc.nasa.gov/apod/lib/uranus.html ] atmosphere, which has been digitally enhanced with false color. Three other planets in our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] are known to have rings: Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950802.html ], Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ], and Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap950817.html ]. Four of Uranus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/uranus.html ]' moons are visible outside the ring plane. The rings of Uranus [ http://ringside.arc.nasa.gov/www/uranus/uranus.html ] were discovered from ground-based observations in 1977. |
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Alpha Centauri: The Closest
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| Title |
Alpha Centauri: The Closest Star System |
| Explanation |
The closest star system to the Sun is the Alpha Centauri system [ http://monet.physik.unibas.ch/~schatzer/Alpha-Centauri.html ]. Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star [ http://cassfos02.ucsd.edu/public/nearest.html ]. The bright stars Alpha Centauri A and B form a close binary as they are separated by only 23 times the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ]- Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960521.html ] distance - slightly greater than the distance between Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] and the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ]. In the above picture, the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light. The Alpha Centauri system is not visible in much of the northern hemisphere. Alpha Centauri A, also known as Rigil Kentaurus [ http://www.astro.wisc.edu/~dolan/constellations/hr/5459.html ], is the brightest star in the constellation of Centaurus [ http://galileo.gmu.edu/constellation/CEN.html ] and is the fourth brightest star [ http://www.entrenet.com/mizar/brt_star.html ] in the night sky. Sirius [ http://www.astro.wisc.edu/~dolan/constellations/hr/2491.html ] is the brightest even thought it is more than twice as far away. By an exciting coincidence, Alpha Centauri A is the same type of star as our Sun, causing many to speculate that it might contain planets that harbor life. |
|
Ringed Planet Uranus
| Title |
Ringed Planet Uranus |
| Explanation |
Yes it does look like Saturn, but Saturn is only one of four [ http://antwrp.gsfc.nasa.gov/apod/ap020616.html ] giant [ http://antwrp.gsfc.nasa.gov/apod/ap020215.html ] ringed [ http://antwrp.gsfc.nasa.gov/apod/ap981020.html ] planets [ http://ringmaster.arc.nasa.gov/neptune/neptune.html ] in our Solar System. And while Saturn has the brightest rings, this system of rings and moons actually belongs to planet Uranus, imaged here [ http://www.eso.org/outreach/press-rel/pr-2002/ phot-31-02.html ] in near-infrared light by the Antu [ http://antwrp.gsfc.nasa.gov/apod/ap000707.html ] telescope at the ESO Paranal Observatory in Chile. Since gas giant Uranus' [ http://www.seds.org/nineplanets/nineplanets/uranus.html ] methane-laced atmosphere absorbs sunlight at near-infrared wavelengths the planet appears substantially darkened, improving the contrast between the otherwise relatively bright planet and the normally faint rings. In fact, the narrow Uranian rings [ http://ringmaster.arc.nasa.gov/uranus/ uranus.html ] are all but impossible to see in visible light with earthbound telescopes and were discovered [ http://tdc-www.harvard.edu/occultations/ uranus25/ ] only in 1977 as careful astronomers noticed the then unknown rings blocking light from background stars. The rings are thought to be younger than 100 million years and may be formed of debris from the collision of a small moon with a passing comet or asteroid-like object. With moons [ http://antwrp.gsfc.nasa.gov/apod/ap000930.html ] named for characters [ http://antwrp.gsfc.nasa.gov/apod/ap990227.html ] in Shakespeare's plays, the distant ringed world Uranus [ http://vraptor.jpl.nasa.gov/voyager/vgrur_fs.html ] was last visited in 1986 by the Voyager 2 spacecraft. |
|
NGC 5882: A Small Planetary
…
| Title |
NGC 5882: A Small Planetary Nebula |
| Explanation |
Will most stars one day look like this? Pictured above is the planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/lib/planetary.html ] NGC 5882, captured [ http://scivax.stsci.edu/~hamilton/nuggets/HST_NUGGETS.HTML ] by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ]. Although planetary nebulae [ http://zebu.uoregon.edu/~imamura/208/feb22/feb22.html ] can appear similar to planets like Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] and Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap950817.html ], they are actually gas [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] clouds surrounding stars typically hundreds of light years away. Planetary nebula [ http://home.cc.umanitoba.ca/~umbole/pneb.html ] form when a typical star [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#star ] completes fusion [ http://fusedweb.pppl.gov/default.html ] in its core and ejects an outer envelope of gas - usually about 10 percent of the star's initial mass. This gas shell dims in about 50,000 years - short compared to the lifetimes of stars [ http://xalph.ast.cam.ac.uk/public/niel/scales.html ]. Therefore, although only about 1000 planetary nebula [ http://wonka.physics.ncsu.edu/www/Astro/Research/Plneb/ ] are known in our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960213.html ], it is thought that most stars go through this phase. Green light is emitted when oxygen [ http://web.cetlink.net/~yinon/o.html ] ions acquire electrons from the surrounding gas. |
|
Alpha Centauri: The Closest
…
| Title |
Alpha Centauri: The Closest Star System |
| Explanation |
The closest star system to the Sun is the Alpha Centauri system [ http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html ]. Of the three stars in the system, the dimmest -- called Proxima Centauri [ http://antwrp.gsfc.nasa.gov/apod/ap020715.html ] -- is actually the nearest star [ http://antwrp.gsfc.nasa.gov/apod/ap010318.html ]. The bright stars Alpha Centauri [ http://www.astro.uiuc.edu/~kaler/sow/rigil-kent.html ] A and B form a close binary [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] as they are separated by only 23 times the Earth- Sun distance [ http://neo.jpl.nasa.gov/glossary/au.html ] - slightly greater than the distance between Uranus [ http://www.nineplanets.org/uranus.html ] and the Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ]. In the above picture [ http://www.eso.org/outreach/press-rel/pr-2003/pr-05-03.html ], the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light. The Alpha Centauri system [ http://www.eso.org/outreach/press-rel/pr-2003/pr-05-03.html ] is not visible in much of the northern hemisphere. Alpha Centauri A, also known as Rigil Kentaurus [ http://www.astro.wisc.edu/~dolan/constellations/hr/5459.html ], is the brightest star in the constellation of Centaurus [ http://www.astronomical.org/constellations/cen.html ] and is the fourth brightest star in the night sky. Sirius [ http://antwrp.gsfc.nasa.gov/apod/ap000611.html ] is the brightest even thought it is more than twice as far away. By an exciting coincidence, Alpha Centauri [ http://www.solstation.com/stars/alp-cent3.htm ] A is the same type of star as our Sun [ http://www.nineplanets.org/sol.html ], causing many to speculate [ http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html ] that it might contain planets that harbor life. |
|
Lightning on Jupiter
| Title |
Lightning on Jupiter |
| Explanation |
Does lightning occur only on Earth? Spacecraft in our Solar System have detected radio signals consistent with lightning [ http://wwwghcc.msfc.nasa.gov/lisotd.html ] on other planets, including Venus [ http://www.seds.org/nineplanets/nineplanets/venus.html ], Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ], Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ], and Neptune [ http://www.seds.org/nineplanets/nineplanets/neptune.html ]. In the above photograph [ http://galileo.ivv.nasa.gov/callisto/050197.html ], optical flashes from Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970109.html ] were photographed recently by the Galileo orbiter [ http://galileo.ivv.nasa.gov/mission.html ]. Each of the circled dots indicates lightning [ http://www.nofc.forestry.ca/~kanderso/ltgfaq.html ]. The numbers label lines of latitude [ http://www.met.fsu.edu/explores/latlon.html ]. The size of the largest spot is about 500 kilometers across and might be high clouds illuminated by several bright lightning strokes. |
|
An Auroral Ring on Jupiter
| Title |
An Auroral Ring on Jupiter |
| Explanation |
Do other planets have aurora? Terrestrial [ http://work.ucsd.edu:5141/cgi-bin/http_webster?terrestrial ] and spacecraft observations have found evidence for aurora on Venus [ http://www.seds.org/nineplanets/nineplanets/venus.html ], Mars [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://www.seds.org/nineplanets/nineplanets/mars.html ], Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ], Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ], and Neptune [ http://www.seds.org/nineplanets/nineplanets/neptune.html ]. In the above false-color photograph [ http://galileo.ivv.nasa.gov/callisto/043097.html ], a good portion of an auroral ring [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996BAAS%2E%2E%2E28%2E2123P&db_key=AST&nosetcookie=1 ] was captured recently in optical light by the Galileo spacecraft [ http://galileo.ivv.nasa.gov/spacecraft.html ] in orbit around Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://antwrp.gsfc.nasa.gov/cgi-bin/cossc/apod_search?jupiter ]. Auroral rings [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://www.geo.mtu.edu/weather/aurora/ ] encircle a planet's magnetic pole, and result from charged particles spiraling down magnetic field lines. Although the surroundings near Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ] are much different than Earth [ http://antwrp.gsfc.nasa.gov/apod/ap961230.html ], the auroral rings [ http://antwrp.gsfc.nasa.gov/apod/ap970402.html ] appear similar. |
|
Retrograde Mars
| Title |
Retrograde Mars |
| Explanation |
Why would Mars appear to move backwards? Most of the time, the apparent motion of Mars [ http://www.nineplanets.org/mars.html ] in Earth's sky [ http://antwrp.gsfc.nasa.gov/apod/ap010827.html ] is in one direction, slow but steady in front of the far distant stars. About every two years, however, the Earth passes Mars [ http://antwrp.gsfc.nasa.gov/apod/ap030902.html ] as they orbit around the Sun. During the most recent such pass in August, Mars loomed [ http://antwrp.gsfc.nasa.gov/apod/ap030828.html ] particularly large and bright [ http://antwrp.gsfc.nasa.gov/apod/ap030827.html ]. Also during this time, Mars appeared to move backwards in the sky, a phenomenon called retrograde motion [ http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html ]. Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop [ http://mars.jpl.nasa.gov/allabout/nightsky/nightsky04.html ] in the sky. At the top of the loop, Earth passed Mars and the retrograde motion [ http://astron.berkeley.edu/~ay7/html/homework/hw1/node3.html ] was the highest. Retrograde motion [ http://antwrp.gsfc.nasa.gov/apod/ap011220.html ] can also be seen for other Solar System [ http://www.nineplanets.org/overview.html ] planets. In fact, by coincidence, the dotted line to the right of the image center is Uranus doing the same thing. |
|
Solar System Portrait
| Title |
Solar System Portrait |
| Explanation |
On another Valentine's Day [ http://www.poets.org/poems/poems.cfm?prmID=1166 ] (February 14, 1990), cruising four billion miles from the Sun, the Voyager 1 [ http://antwrp.gsfc.nasa.gov/apod/ap031120.html ] spacecraft looked back to make this first ever family portrait [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00451 ] of our Solar System. The complete portrait is a 60 frame mosaic [ http://nssdc.gsfc.nasa.gov/photo_gallery/ photogallery-solarsystem.html ] made from a vantage point 32 degrees above the ecliptic plane [ http://antwrp.gsfc.nasa.gov/apod/ap001014.html ]. Voyager's wide angle camera frames sweep through the inner Solar System (far left) linking up with gas giant Neptune, at the time the Solar System's [ http://www.seds.org/nineplanets/nineplanets/overview.html ] outermost planet (scroll right). Positions [ http://nssdc.gsfc.nasa.gov/image/planetary/solar_system/ family_diagram.jpg ] for Venus, Earth [ http://www.seds.org/billa/psc/pbd.html ], Jupiter, Saturn, Uranus, and Neptune are indicated by the corresponding letters while the Sun is the bright spot near the center of the circle of frames. The inset frames [ http://antwrp.gsfc.nasa.gov/apod/ap980517.html ] for each of the planets are from Voyager's narrow field camera. Unseen in the portrait are Mercury [ http://www.psrd.hawaii.edu/Jan97/Mercury Unveiled.html ], too close to the Sun to be detected, and Mars, unfortunately hidden by sunlight scattered in the camera's optical system. Small, faint Pluto's [ http://antwrp.gsfc.nasa.gov/apod/ap011018.html ] position was not covered. |
|
Irregular Moons Discovered A
…
| Title |
Irregular Moons Discovered Around Uranus |
| Explanation |
Where did these two irregular moons of Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ] originate? Last week two previously undiscovered moons [ http://www.cita.utoronto.ca/~gladman/utpress.html ] of the distant gas planet were confirmed [ http://cfa-www.harvard.edu/iauc/06700/06765.html ], the first in irregular orbits. All fifteen previously known moons [ http://www.seds.org/nineplanets/nineplanets/uramoons.html ] of Uranus [ http://bang.lanl.gov/solarsys/uranus.htm ] are 'regular', circling near the planet's equator. Most of these were discovered by the passing Voyager 2 spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] in 1986. These newly discovered moons [ http://www.news.cornell.edu/science/Oct97/new_moons.hrs.html ] are thought to be odd-shaped and about 100 km across. They are considered irregular, though, because they orbit in odd directions and far from Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ]. If Uranus' irregular moons have the same origin as those orbiting Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ], Saturn [ http://pds.jpl.nasa.gov/planets/welcome/saturn.htm ], and Neptune [ http://spacelink.msfc.nasa.gov/Instructional.Materials/Curriculum.Materials/Sciences/Astronomy/Our.Solar.System/Neptune/ ], then they were probably caught from orbits around the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960518.html ]. Moons like this are discovered by their motion. One of these moons is shown above [ http://www.cita.utoronto.ca/~gladman/ ] as the circled point of light moving from left to right. (To stop the movie from repeating, click "stop" on most browsers.) |
|
A Sky Full Of Planets
| Title |
A Sky Full Of Planets |
| Explanation |
Look up tonight [ http://www.cnn.com/TECH/9712/01/heavenly.show.ap/ ]. Just after sunset, the crescent moon and all five "naked-eye" planets (Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap971130.html ], Venus [ http://antwrp.gsfc.nasa.gov/apod/ap971014.html ], Mars [ http://antwrp.gsfc.nasa.gov/apod/ap970528.html ], Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap971030.html ], and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap970829.html ]) will be visible (depending on your latitude), lying near our solar system's ecliptic plane [ http://antwrp.gsfc.nasa.gov/apod/ap970927.html ]. Venus and Jupiter will shine brilliantly as the brightest "stars" in the sky, but Mercury will be near the horizon and hard to see. A pair of binoculars will also reveal Uranus and Neptune and observers with a telescope and a good site may even be able to glimpse faint Pluto just above the Western horizon in the fading twilight (not shown on the chart above). Enjoy this lovely spectacle any clear night [ http://www.skypub.com/whatsup/dec97sky.html ] through about December 8. A similar gathering is expected in May 2000 [ http://www.skypub.com/special/alignmnt/whypanic.html ] but the planets will be hidden from view by the solar glare. A night sky as full of planets as this one will occur again though ... in about 100 years. |
|
Uranian Moons, Rings, And Cl
…
| Title |
Uranian Moons, Rings, And Clouds |
| Explanation |
The giant planet Uranus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/uranus.html ] is faint and featureless when viewed in visible light [ http://antwrp.gsfc.nasa.gov/apod/ap971115.html ]. But this pair [ http://oposite.stsci.edu/pubinfo/PR/97/36/a-js.html ] of near-infrared mosaics [ http://oposite.stsci.edu/pubinfo/PR/97/36.html ] from the Hubble Space Telescope's NICMOS camera [ http://www.stsci.edu/ftp/instrument_news/NICMOS/nicmos_dvlp.html ] reveals moons, rings, and clouds of this distant gas planet [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html ]. The color coded images highlight different atmospheric layers - blue represents the deepest layers while the highest cloud features have a reddish tinge. Racing around the planet, high, bright clouds are seen to move substantially between the two pictures taken only ninety minutes apart. Ring systems [ http://antwrp.gsfc.nasa.gov/apod/ap960430.html ] are a common to the solar system's [ http://antwrp.gsfc.nasa.gov/apod/ap961214.html ] giant planets. Here the main Uranian ring [ http://ringside.arc.nasa.gov/www/uranus/uranus.html ] seems to vary in width and is clearly brightest near the top. The eight specks beyond the ring system are small Uranian moons [ http://www.seds.org/nineplanets/nineplanets/uramoons.html ] which also show counter-clockwise motion [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ] over ninety minutes as traced by the arrows [ http://antwrp.gsfc.nasa.gov/apod/ap970131.html ] on the right hand image. |
|
Hamlet of Oberon
| Title |
Hamlet of Oberon |
| Explanation |
What's in a name? [ http://the-tech.mit.edu/Shakespeare/Quotes/bart.RJ.html#22 ] Since 1919, the International Astronomical Union [ http://www.intastun.org ] has been charged with the task [ http://the-tech.mit.edu/Shakespeare/Quotes/bart.LoveLost.html#3 ] of establishing "conventional" nomenclature [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/nomen.html ] for planets, satellites, and surface features. For the remote Uranian system [ http://antwrp.gsfc.nasa.gov/apod/ap971126.html ] of moons, namesakes from Shakespearean works [ http://the-tech.mit.edu/Shakespeare/works.html ] have been chosen. Thus Oberon [ http://antwrp.gsfc.nasa.gov/apod/ap960408.html ], king of the mid-summer night fairies, is also Uranus' most distant and second largest moon [ http://antwrp.gsfc.nasa.gov/apod/ap970111.html ]. Hamlet is the tragically dark, large and princely crater on its surface [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/uranus/obercrat.html ] (right of center). The above image represents known surface features of Oberon [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/wall/oberon.html ] and was constructed by the U.S. Geological Survey (USGS) based on data from NASA's robot explorer Voyager 2 [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ]. In 1986, Voyager 2 flew through the Uranian system [ http://vraptor.jpl.nasa.gov/voyager/vgrur_fs.html ] - so far it has been the only spacecraft to do so [ http://nssdc.gsfc.nasa.gov/imgcat/html/mission_page/ UR_Voyager_2_page1.html ]. |
|
Closer To Beta Pic
| Title |
Closer To Beta Pic |
| Explanation |
What did our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap961214.html ] look like as the planets were forming [ http://antwrp.gsfc.nasa.gov/apod/ap961207.html ]? Since the 1980s, astronomers have been pointing toward Beta Pictoris [ http://antwrp.gsfc.nasa.gov/apod/ap971128.html ], a young, sun-like star a mere 50 light-years distant, as a likely example. Beta Pic is surrounded by a disk of dust [ http://antwrp.gsfc.nasa.gov/apod/ap960119.html ] which we view nearly edge-on. The dust disk shines by reflected starlight and has been examined with ever increasing detail to search for signs [ http://hrssun.gsfc.nasa.gov/ghrsgh/02b.html ] of planetary formation. The trick is to follow the disk [ http://www.ifa.hawaii.edu/~jewitt/beta.html ] as close in to the star as possible, without being overwhelmed by the direct starlight. To make this Hubble Space Telescope image [ http://oposite.stsci.edu/pubinfo/pr/1998/03/a-js.html ], a coronagraph [ http://www.mpia-hd.mpg.de/MPIA/Projects/STARS/members/ kalas/corona.html ] was used to block the direct starlight and achieve the closest view yet. The false color picture shows [ http://oposite.stsci.edu/pubinfo/pr/1998/03/pr-gsfc.html ] the inner section of the dusty disk to within nearly 1.5 billion miles of the star itself, about the scale of the orbit of Uranus. The obvious warp is indirect evidence [ http://oposite.stsci.edu/pubinfo/pr/1998/03/ ] that a planet now orbits this young sun [ http://antwrp.gsfc.nasa.gov/apod/ap970611.html ], slightly inclined to the disk. The planet's gravitational pull would produce the visible distortion. |
|
Lightning on Earth
| Title |
Lightning on Earth |
| Explanation |
Nobody knows what causes lightning. It is known that charges [ http://physics.bu.edu/~duffy/PY106/Charge.html ] slowly separate in some clouds [ http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml ] causing rapid electrical discharges [ http://van.hep.uiuc.edu/van/qa/section/Electricity_and_Magnets/Stuff_that_Sparks/20020722034338.htm ] (lightning), but how electrical charges [ http://www.sciencemadesimple.com/static.html ] get separated in clouds [ http://www.geo.mtu.edu/department/classes/ge406/tjbrabec/cloud.html ] remains a topic of much research. Nevertheless, lightning [ http://wvlightning.com/info.html ] bolts are common in clouds during rainstorms, and on average 6000 lightning bolts occur between clouds and the Earth every minute. Above [ http://www.astro.umd.edu/openhouse/gallery/2004-07KPNO/index.html ], several lightning strokes were photographed under a starry sky behind Kitt Peak National Observatory [ http://www.noao.edu/outreach/kpoutreach.html ] near Tucson, Arizona [ http://www.state.az.us/ ]. Lightning [ http://www.nationalgeographic.com/lightning/ ] has also been found on the planets Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap971216.html ], Saturn [ http://news.bbc.co.uk/2/hi/science/nature/3920597.stm ], and Uranus [ http://www.spacetoday.org/SolSys/Uranus/UranusVoyager.html ]. NASA [ http://www.nasa.gov/ ] launched the TRMM mission [ http://trmm.gsfc.nasa.gov/ ] in 1997 that continues to measure rainfall and lightning [ http://thunder.msfc.nasa.gov/primer/ ] on planet Earth [ http://antwrp.gsfc.nasa.gov/apod/ap010204.html ]. |
|
A Sharper View of a Tilted P
…
| Title |
A Sharper View of a Tilted Planet |
| Explanation |
These sharp views [ http://www2.keck.hawaii.edu/news/science/uranus/ index.html ] of tilted gas giant Uranus [ http://www.nineplanets.org/uranus.html ] show dramatic details of the planet's atmosphere and ring system [ http://ringmaster.arc.nasa.gov/uranus/uranus.html ]. The remarkable ground-based images [ http://www.news.wisc.edu/10402.html ] were made using a near-infrared camera and the Keck Adaptive Optics system to reduce the blurring effects of Earth's atmosphere. Recorded in July, the pictures show [ http://www.news.wisc.edu/newsphotos/ uranus2.html ] two sides of Uranus (careful how you pronounce [ http://www.nineplanets.org/say/uranus.au ] that ...). In both, high, white cloud features are seen mostly in the northern (right hand) hemisphere, with medium level cloud bands in green and lower level clouds in blue. The artificial color scheme lends a deep reddish tint to the otherwise faint rings [ http://antwrp.gsfc.nasa.gov/apod/ap030115.html ]. Because of the severe tilt of its rotational axis, seasons on Uranus [ http://www.haydenplanetarium.org/hp/vo/ava/avapages/ P0418uranseas.html ] are extreme and last nearly 21 Earth years on the distant planet [ http://nssdc.gsfc.nasa.gov/ planetary/factsheet/uranusfact.html ]. Uranus is now slowly approaching its southern autumnal equinox - the beginning of fall in the southern hemisphere - in 2007. |
|
Infrared Uranus
| Title |
Infrared Uranus |
| Explanation |
The Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ]'s third largest planet usually looks quite dull. Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ] typically appears as a featureless small spot in a small telescope or a featureless large orb [ http://antwrp.gsfc.nasa.gov/apod/ap971115.html ] in a large telescope. Last August, however, the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap970306.html ] was able to photograph Uranus [ http://oposite.stsci.edu/pubinfo/pr/1998/35/index.html ] in infrared [ http://www.ipac.caltech.edu/Outreach/Edu/discovery.html ] light, where the distant planet better shows its unusual clouds, rings, and moons [ http://antwrp.gsfc.nasa.gov/apod/ap971126.html ]. Recent analysis indicates that clouds seen here in orange appear to circle Uranus [ http://www.hawastsoc.org/solar/eng/uranus.htm ] at speeds in excess of 500 kilometers per hour. Comparisons to earlier photographs [ http://antwrp.gsfc.nasa.gov/apod/ap971126.html ] show a slight precession shift in the brightest of Uranus' rings [ http://ringside.arc.nasa.gov/www/uranus/uranus.html ]. Several of Uranus' numerous small moons [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ] are visible. |
|
Steep Cliffs on Mars
| Title |
Steep Cliffs on Mars |
| Explanation |
Vertical cliffs of nearly two kilometers occur near the North Pole of Mars. Also visible in the above image [ http://www.esa.int/SPECIALS/Mars_Express/SEMLF6D3M5E_1.html ] of the Martian North Polar Cap [ http://antwrp.gsfc.nasa.gov/apod/ap021224.html ] are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash [ http://volcanoes.usgs.gov/Products/Pglossary/ash.html ]. The cliffs are thought to border volcanic caldera [ http://antwrp.gsfc.nasa.gov/apod/ap040526.html ]. Although the sheer drop [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ] of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System [ http://www.nineplanets.org/overview.html ], including the 3.4-kilometer depth of Colca Canyon [ http://www.bootsnall.com/articles/02-08/where-is-the-deepest-canyon-in-the-world-arequipa-peru.html ] on Earth and the 20 kilometer depth of Verona Rupes [ http://www.guinnessworldrecords.com/content_pages/record.asp?recordid=54819 ] on Uranus' moon Miranda [ http://astrogeology.usgs.gov/Projects/BrowseTheGeologicSolarSystem/MirandaBack.html ]. The above image [ http://www.esa.int/SPECIALS/Mars_Express/SEMLF6D3M5E_0.html ], digitally reconstructed into a perspective view [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005LPI....36.1769S ], was taken by the High Resolution Stereo Camera [ http://berlinadmin.dlr.de/Missions/express/kamera/kameraeng.shtml ] on board the ESA [ http://www.esa.int/ ]'s robotic Mars Express spacecraft [ http://www.esa.int/esaSC/120379_index_0_m.html ] currently orbiting Mars [ http://www.nineplanets.org/mars.html ]. |
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Miranda, Chevron, and Alonso
| Title |
Miranda, Chevron, and Alonso |
| Explanation |
Miranda [ http://www.seds.org/nineplanets/nineplanets/miranda.html ] is a bizarre world which surely had a tempest [ http://the-tech.mit.edu/Shakespeare/Comedy/tempest/thetempest.html ]uous past. The innermost of the larger Uranian [ http://pds.jpl.nasa.gov/planets/welcome/uranus.htm ] moons, Miranda is almost 300 miles in diameter and was discovered [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ] in 1948 by American planetary astronomer Gerard Kuiper [ http://sofia.arc.nasa.gov/KAO/home/kuiper_bio.html ]. Examined very closely by the Voyager 2 spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] in 1986, this dark and distant world turned out to be [ http://vraptor.jpl.nasa.gov/voyager/vgrur_fs.html ] quite a surprise [ http://www.pbm.com/~lindahl/music_and_dance.html ]. Miranda was found to display [ http://www.seds.org/nineplanets/nineplanets/pxuranus.html#Miranda ] a unique, bewildering variety of [ http://www.shakespeare.mcgill.ca/resources/ ] terrain leading some to suggest that it has been fractured up to 5 times during its evolution. Along with the famous "chevron" feature, the bright V-shaped area just above center, this composite of the highest resolution images of Miranda shows [ http://www.hawastsoc.org/solar/cap/uranus/vmiranda.htm ] wild juxtapositions of ridges and valleys, older cratered and younger smooth surfaces, and shadowy canyons perhaps 12 miles deep. The large crater (below center) is the 15 mile wide crater Alonso [ http://the-tech.mit.edu/Shakespeare/Comedy/tempest/ thetempest.dp.html ]. |
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Aerogel For STARDUST
| Title |
Aerogel For STARDUST |
| Explanation |
On February 7th, this honey comb [ http://stardust.jpl.nasa.gov/photo/spacecraft1.html ] of aluminum cells filled with aerogel [ http://www.Aerogels.com/ ] was launched on the STARDUST [ http://stardust.jpl.nasa.gov/ ] mission to interplanetary space. STARDUST's goal is to capture dust from a comet's tail and return to planet Earth - the first sample return [ http://stardust.jpl.nasa.gov/spacecraft/capsule.html ] mission to a comet [ http://encke.jpl.nasa.gov/ ]! This structure represents about 1,000 square centimeters of area for collecting dust trailing within 150 kilometers of the nucleus of P/Wild-2 [ http://stardust.jpl.nasa.gov/comets/wild1.html ]. Comet P/Wild-2 is new to the inner Solar System. Having spent its life in orbit between Jupiter and Uranus, this comet was deflected in 1974 by a close encounter with Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap980801.html ] and now orbits between Jupiter and Earth. Dust from P/Wild-2 should impact the aerogel at high speeds and come to rest leaving carrot-shaped [ http://antwrp.gsfc.nasa.gov/apod/ap981121.html ] tracks in this amazingly tough, transparent, ultra-low density [ http://stardust.jpl.nasa.gov/spacecraft/aerogel.html ] material. Returning to Earth by parachute in 2006, the cometary dust sample will be analyzed for clues to [ http://stardust.jpl.nasa.gov/science/sd-value.html ] the formation and primordial composition of our Solar System. |
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A Solar System Portrait
| Title |
A Solar System Portrait |
| Explanation |
As the Voyager 1 spacecraft [ http://vraptor.jpl.nasa.gov/voyager/vgrfaqs.html ] headed out of our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap980517.html ], it looked back and took a parting family portrait [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-solarsystem.html ] of the Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ] and planets. From beyond Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap990213.html ], our Solar System looks like a bright star surrounded by faint dots. In the above picture [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA00451 ], the Sun is so bright it is blocked out for contrast. The innermost dots visible, labeled E and V for Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ] and Venus [ http://www.nasm.edu/ceps/RPIF/VENUS/rpifvenus.html ], are particularly hard to discern. Gas giants Jupiter [ http://www.jpl.nasa.gov/galileo/Jovian.html ] (J) and Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ] (S) are much more noticeable. The outermost planets visible are Uranus [ http://www.hawastsoc.org/solar/eng/uranus.htm ] (U) and Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap980221.html ] (N). Each planet is shown labeled and digitally enhanced in an inset image. Voyager 1 is only one of four human-made objects to leave our Solar System, the other three being Voyager 2, and Pioneer 10 and Pioneer 11. |
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Uranus' Moon 18
| Title |
Uranus' Moon 18 |
| Explanation |
The discovery was there for the taking. An image of Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ] taken by Voyager [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] 2 as it passed the giant planet 13 years ago apparently recorded a moon that had since gone unnoticed. The image on which Uranus' 18th moon was discovered was freely available [ http://www-pdsimage.JPL.NASA.GOV/PDS/public/jukebox.html ] from NASA. Erich Karkoschka (U. Arizona [ http://science.opi.arizona.edu/ ]) noticed the moon when comparing a 1986 photo to a recent [ http://oposite.stsci.edu/pubinfo/pr/1998/35/index.html ] one taken by the Hubble Space Telescope [ http://www.stsci.edu/hst/ ]. The newly identified moon is hard to see but marked in the above photograph [ http://science.opi.arizona.edu/lasso.acgi?-database=science.fp3&-layout=Fields&-response=%2f%7escience%2fcurrentdetails.htm&-recid=34354&-search ]. Also visible are many other Uranian moons [ http://www.seds.org/nineplanets/nineplanets/uramoons.html ] and background stars. The moon is the 18th known around Uranus [ http://www.hawastsoc.org/solar/eng/uranus.htm ], tying it with Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ] for the most around any planet. |
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Two Hours Before Neptune
| Title |
Two Hours Before Neptune |
| Explanation |
Two hours before closest approach to Neptune [ http://www.seds.org/nineplanets/nineplanets/neptune.html ] in 1989, the Voyager 2 [ http://vraptor.jpl.nasa.gov/voyager/vgrfaqs.html ] robot spacecraft snapped this picture [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-neptune.html ]. Clearly visible for the first time were long light-colored cirrus [ http://earthsky.worldofscience.com/1998/es980706.html ]-type clouds floating high in Neptune's atmosphere [ http://nssdc.gsfc.nasa.gov/photo_gallery/caption/neptune_clouds.txt ]. Shadows of these clouds can even be seen on lower cloud decks. Most of Neptune's atmosphere [ http://antwrp.gsfc.nasa.gov/apod/ap960507.html ] is made of hydrogen [ http://chemlab.pc.maricopa.edu/periodic/h.html ] and helium [ http://chemlab.pc.maricopa.edu/periodic/He.html ], which is invisible. Neptune's blue color therefore comes from smaller amounts of atmospheric methane [ http://www.epa.gov/ghginfo/ ], which preferentially absorbs red light. Neptune [ http://pds.jpl.nasa.gov/planets/welcome/neptune.htm ] has the fastest winds in the Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ], with gusts reaching 2000 kilometers per hour. Recent speculation [ http://www.urel.berkeley.edu/urel_1/CampusNews/PressReleases/releases/9-30-1999a.html ] holds that diamonds [ http://www.sdnhm.org/exhibits/diamonds/facts.html ] may be created in the dense hot conditions that exist under the clouds-tops of Uranus [ http://spacelink.msfc.nasa.gov/Instructional.Materials/Curriculum.Support/Space.Science/Our.Solar.System/Uranus/ ] and Neptune. |
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