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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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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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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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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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Uranian Moons, Rings, And Cl
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| 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. |
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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://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 ]. |
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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. |
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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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