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Earth and 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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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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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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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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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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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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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 ]. |
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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. |
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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. |
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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 ]. |
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A Year of Extraterrestrial F
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| 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 ]. |
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Liquid Lakes on Saturn's Tit
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| 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. |
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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 ]. |
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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/ ]. |
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Nashville Four Planet Skylin
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| 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. |
|
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. |
|
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. |
|
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/ ] |
|
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 ]. |
|
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/ ] |
|
A Portrait of Saturn from Ti
…
| Title |
A Portrait of Saturn from Titan |
| Explanation |
This artistic portrait [ http://sci.esa.int/content/searchimage/ searchresult.cfm?aid=12&cid=387&ooid=18425 ] of Saturn [ http://www.otenet.gr/everyday/ saturday.html ] depicts how it might look from Titan [ http://www.seds.org/nineplanets/nineplanets/ titan.html ], Saturn's largest moon. In the foreground sits ESA's Huygens probe [ http://sci.esa.int/home/huygens/index.cfm ], which will be released by NASA's Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] and parachute to Titan's surface. Cassini will [ http://www.jpl.nasa.gov/cassini/english/ ] reach Saturn in 2004 and release the Huygens probe [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ probe.html ] later that year. Titan [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html ] is one of only two moons in the Solar System [ http://space.jpl.nasa.gov ] to have an atmosphere. It has been suggested Titan might have gasoline-like lakes and an atmospheric chemistry like that [ http://www.llnl.gov/str/Macintosh.html ] found on early Earth. The Cassini spacecraft was launched in October 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and has now traveled beyond Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap010808.html ]. |
|
Moon Over Mongolia
| Title |
Moon Over Mongolia |
| Explanation |
Fighting clouds and the glow of city lights, a young Moon shines over the western horizon of Mongolia's [ http://www.mol.mn/ ] capital, Ulaan-Baatar [ http://www.cia.gov/cia/publications/factbook/geos/ mg.html ]. The thin sunlit crescent [ http://www.allthesky.com/various/earthshine.html ] is about 2 days old and strongly over exposed in this image taken on March 10, 1997. The night side of the Moon is also visible due to earthshine [ http://www.bbso.njit.edu/Research/EarthShine/ ] - sunlight reflected from the Earth to the Moon. Just below the Moon, bright Saturn [ http://nssdc.gsfc.nasa.gov/photo_gallery/ photogallery-saturn.html ] shines through the clouds. Skygazers [ http://www.spaceweather.com/planets/gallery_nov01.html ] will have a chance to watch the Moon actually pass in front [ http://antwrp.gsfc.nasa.gov/apod/ap010908.html ] of the ringed planet in February, March, and April this year. In fact, an excellent lunar occultation of Saturn will be visible from parts of North America on February 20th [ http://skyandtelescope.com/observing/objects/occultations/ article_297_1.asp ] as Saturn disappears behind the dark limb of a first quarter Moon. Some may even take this opportunity to search for Saturn's lost ring [ http://www.lunar-occultations.com/iota/planets2002/ 0221ring.htm ]. |
|
Ski Enceladus
| Title |
Ski Enceladus |
| Explanation |
A small inner moon of Saturn [ http://csep10.phys.utk.edu/astr161/lect/saturn/moons.html ], Enceladus is only about 500 kilometers in diameter. But the cold, distant world does reflect over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as new-fallen snow. Seen here [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00347 ] in a mosaic of Voyager [ http://vraptor.jpl.nasa.gov/voyager/ vgrsat_fs.html ] 2 images from 1981, Enceladus [ http://solarsystem.nasa.gov/features/planets/saturn/ enceladus.html ] shows a variety of surface features and very few impact craters - indicating that it is an active world even though this ice moon should have completely cooled off long ago [ http://www.sciam.com/explorations/010697sagan/ 010697sagan1.html ]. In fact the fresh, resurfaced appearance of Enceladus suggests that an internal mechanism, perhaps driven by tidal pumping, generates heat and supplies liquid water to geysers or water volcanos [ http://pirlwww.lpl.arizona.edu/HIIPS/ Cryovolcanism/ ]. Since Enceladus orbits within the tenuous outer E [ http://www.astro.spbu.ru/staff/dikarev/valery/ering.html ] ring [ http://ringmaster.arc.nasa.gov/saturn/ saturn.html#IMAGES ] of Saturn, the moon's surface may be kept snow-bright as it is continuously bombarded with icy ring particles. Eruptions [ http://www.jpl.nasa.gov/cassini/Mission/pix/ enceladus_lg.gif ] on Enceladus itself would in turn supply material to the E ring. Interplanetary [ http://www.jpl.nasa.gov/cassini/Mission/ ] ski [ http://antwrp.gsfc.nasa.gov/apod/ap990401.html ] bums take note: tiny Enceladus has only about one hundredth the surface gravity of planet Earth [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA03439 ]. |
|
Earth Rise
| Title |
Earth Rise |
| Explanation |
During 1968, the Apollo 8 [ http://www.lpi.usra.edu/expmoon/Apollo8/Apollo8.html ] crew flew from the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap001127.html ] to the Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ] and back. The crew, consisting of Frank Borman [ http://www.jsc.nasa.gov/Bios/htmlbios/borman-f.html ], James Lovell [ http://www.jsc.nasa.gov/Bios/htmlbios/lovell-ja.html ], and William Anders [ http://www.jsc.nasa.gov/Bios/htmlbios/anders-wa.html ], were launched atop a Saturn V rocket [ http://www.apollosaturn.com/frame-sv.htm ] on December 21, circled the Moon ten times in their command module, and landed back on Earth on December 27. The Apollo 8 [ http://www.nasm.edu/apollo/AS08/a08.htm ] mission's impressive list of firsts includes: the first humans to journey to the Earth's Moon [ http://www.nineplanets.org/luna.html ], the first manned flight using the Saturn V [ http://antwrp.gsfc.nasa.gov/apod/ap010525.html ], and the first to photograph the Earth from deep space. The famous picture above [ http://images.jsc.nasa.gov/images/pao/AS8/10074963.htm ], showing the Earth rising above [ http://antwrp.gsfc.nasa.gov/apod/ap010713.html ] the Moon's limb as seen from lunar orbit, was a marvelous gift to the world. |
|
The Last Moon Shot
| Title |
The Last Moon Shot |
| Explanation |
In 1865 Jules Verne predicted the invention of a space capsule that could carry people. In his science fiction story "From the Earth to the Moon" [ ftp://ftp.cdrom.com/.22/gutenberg/etext93/moon10.txt ], he outlined his vision of constructing a cannon in Florida so powerful that it could shoot a "Projectile-Vehicle" carrying three adventurers to the Moon. Over 100 years later, NASA, guided by Wernher Von Braun [ http://www.hq.nasa.gov/office/pao/History/Biographies/biosa-d.html ]'s vision, produced the Saturn V rocket [ http://pscinfo.pscni.nasa.gov/online/msfc/spacelink2.html ]. This rocket [ http://antwrp.gsfc.nasa.gov/apod/ap950829.html ] turned Verne's fiction into fact, launching 9 Apollo Lunar missions and allowing 12 astronauts to walk on the Moon. Pictured above is the last moon shot, Apollo 17 [ http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo17info.html ], awaiting a night launch in December of 1972. Spot lights play on the rocket and launch pad while the full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap950903.html ] looms in the background. Humans have not walked on the lunar surface since. [ http://ees5-www.lanl.gov/Apollo/apollo.epilog.html ] Should we return to the Moon? [ http://www.ari.net/back2moon.html ] Tomorrow's picture: White Dwarfs Cool |
|
Skylab Over Earth
| Title |
Skylab Over Earth |
| Explanation |
Skylab [ http://www.ksc.nasa.gov/history/skylab/skylab.html ] was an orbiting laboratory launched by a Saturn V rocket [ http://antwrp.gsfc.nasa.gov/apod/ap950829.html ] in May 1973. Skylab [ http://heasarc.gsfc.nasa.gov/Images/pretty_pictures_skylab.html ] was visited three times by NASA astronauts who sometimes stayed as long as two and a half months. Many scientific tests were preformed on Skylab, including astronomical observations in ultraviolet [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#uv ] and X-ray [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ] light. Some of these observations yielded valuable information about Comet Kohoutek, our Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] and about the mysterious X-ray background - radiation that comes from all over the sky. Skylab fell back to earth on 11 July 1979. Tomorrow's picture: X-Raying the Moon |
|
Titan: Saturn's Smog Moon
| Title |
Titan: Saturn's Smog Moon |
| Explanation |
The largest moon of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ] is a rare wonder. Titan is the only one of Saturn [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/titan.html ]'s moons with an atmosphere, and one of only two moons in the Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] with this distinction (Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap950817.html ]'s Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] is the other). Titan [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/titan.html ]'s thick cloudy atmosphere is mostly nitrogen, like Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ]'s, but contains much higher percentages of "smog-like" chemicals such as methane and ethane. The smog may be so thick that it actually rains "gasoline-like" liquids. The organic nature of some of the chemicals found in Titan's atmosphere cause some to speculate that Titan may harbor life! Because of its thick cloud cover, however, Titan's actual surface properties remain mysterious. Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 1 flew by in 1980 taking the above picture, and recently much has been learned from Hubble Space Telescope observations [ http://www.stsci.edu/pubinfo/PR/94/55.html ]. The Cassini mission [ http://www.jpl.nasa.gov/mip/cassini.html ] currently scheduled for launch in 1997 will map Titan's surface, helping to solve some of its mysteries. |
|
Dusk of the Planets
| Title |
Dusk of the Planets |
| Explanation |
A great grouping of planets [ http://www.nineplanets.org/ ] is now visible [ http://CarnegieScienceCenter.org/exhibits/planet_calendar.asp ] to the west just after sunset. Over the next two weeks, Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap010819.html ], Venus [ http://antwrp.gsfc.nasa.gov/apod/ap010916.html ], Earth, Mars [ http://antwrp.gsfc.nasa.gov/apod/ap010628.html ], Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap020205.html ], and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap020215.html ] -- the innermost six planets of our Solar System [ http://www.nineplanets.org/overview.html ] -- can be seen in a single knowing glance. The image on the left [ http://www.astropix.com/HTML/H_OTHER/PLANETS.HTM ] captured them all in one frame. Connecting the planetary dots delineates the edge-on ecliptic [ http://antwrp.gsfc.nasa.gov/apod/ap990529.html ], the plane in which the planets orbit the Sun [ http://csep10.phys.utk.edu/astr161/lect/retrograde/copernican.html ]. The shot was taken on April 23 near Chatsworth, New Jersey [ http://www.state.nj.us/ ], USA [ http://www.cia.gov/cia/publications/factbook/geos/us.html ], and even includes scattered light from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap000403.html ] and the Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ]. Besides the planets, the Pleiades [ http://antwrp.gsfc.nasa.gov/apod/ap010506.html ] and Hyades [ http://www.astro.uiuc.edu/~kaler/sow/hyades-p.html ] open clusters [ http://www.seds.org/messier/open.html ] of stars are visible [ http://www.planetary.org/html/news/articlearchive/headlines/2002/alignment.htm ]. |
|
Dione's Lagrange Moon Helene
| Title |
Dione's Lagrange Moon Helene |
| Explanation |
Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ]'s moon Helene [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/helene.html ] is very unusual in that it circles Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950801.html ] near the orbit of a bigger moon: Dione [ http://antwrp.gsfc.nasa.gov/apod/ap951009.html ]. Helene is situated in what is called a "Lagrange point" of Dione - a place of stability created by Dione's gravity. Were Helene [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/dione.html#helene ] to stray slightly from its orbit 1/6 ahead of Dione, the larger moon's gravity would cause Helene to move back toward the Lagrange point. Many massive orbital bodies have stable Lagrange points, including the Earth and Moon. Helene was discovered from the ground by P. Laques & J. Lecacheux in 1980. The photograph above was taken by Voyager 2 as it passed Saturn in 1981. NASA's Cassini [ http://newproducts.jpl.nasa.gov/calendar/cassini.html ] mission to Saturn is currently scheduled for launch in October 1997. |
|
Rhea: Saturn's Second Larges
…
| Title |
Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/rhea.html ] is the second largest moon of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ], behind Titan [ http://antwrp.gsfc.nasa.gov/apod/ap950923.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/rhea.html ]'s rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. The above photograph was taken with the Voyager 1 spacecraft in 1980. |
|
Planets Over Stonehenge
| Title |
Planets Over Stonehenge |
| Explanation |
Stonehenge [ http://antwrp.gsfc.nasa.gov/apod/ap990912.html ], four thousand year old [ http://antwrp.gsfc.nasa.gov/apod/ap980408.html ] monument to the Sun [ http://www.hao.ucar.edu/public/education/archeoslides/ index.html ], provides an appropriate setting for this delightful snapshot [ http://www.astrocruise.com/planets.htm ] of the Sun's children [ http://www.seds.org/nineplanets/nineplanets/ ] gathering in planet Earth's sky. While the massive stone [ http://www.amherst.edu/~ermace/sth/poetry.html ] structure dates from around 2000 B.C. [ http://mathforum.org/dr.math/problems/masell10.1.97.html ], this arrangement of the visible planets [ http://skyandtelescope.com/observing/objects/planets/ article_572_1.asp ] was recorded only a few days ago on the evening of May 4th, 2002 A.D. Bright Jupiter stands highest above the horizon at the upper left. A remarkable, almost equilateral triangle [ http://mathforum.org/dr.math/faq/formulas/ faq.triangle.html ] formed by Saturn (left), Mars (top), and Venus (right) is placed just above the stones near picture center. Fighting the glow of the setting sun, Mercury can be spotted closest to the horizon, below and right of the planetary triad. Still easy to enjoy [ http://science.nasa.gov/headlines/y2002/24apr_relax.htm ] for casual sky gazers, this photogenic and slowly shifting planetary grouping [ http://science.nasa.gov/spaceweather/planets/ gallery_may02.html ] will be joined by a young crescent [ http://antwrp.gsfc.nasa.gov/apod/ap020419.html ] Moon beginning Monday, May 13. |
|
Natural Saturn On The Cassin
…
| 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 [ http://heritage.stsci.edu/ ] project, 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, the Cassini spacecraft [ http://saturn.jpl.nasa.gov/cassini/index.shtml ]. Cassini flew by Jupiter [ http://www.jpl.nasa.gov/jupiterflyby/ ] at the turn of the millennium and is scheduled to [ http://saturn.jpl.nasa.gov/cassini/english/where/ ] arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ], Cassini will tour the Saturnian system [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], conducting a remote, robotic exploration with software and instruments designed by [ http://www.jpl.nasa.gov/cassini/Partners/ ] denizens of planet Earth. |
|
Io: Moon Over Jupiter
| Title |
Io: Moon Over Jupiter |
| Explanation |
How big is the Jovian moon Io [ http://www.seds.org/nineplanets/ nineplanets/io.html ]? The most volcanic body [ http://volcano.und.nodak.edu/vwdocs/planet_volcano/ other_worlds.html ] in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite [ http://antwrp.gsfc.nasa.gov/apod/ap010127.html ]. Gliding past Jupiter [ http://www.jpl.nasa.gov/jupiterflyby/ ] at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] of active Io [ http://www.jpl.nasa.gov/galileo/moons/io.html ] with the largest [ http://www.seds.org/nineplanets/nineplanets/ datamax.html ] gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ jupiterfact.html ]. Although in the picture Io [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02879 ] appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ joviansatfact.html ]. That puts it nearly 350,000 kilometers above Jupiter's cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap010215.html ], roughly equivalent to the distance between Earth and Moon [ http://antwrp.gsfc.nasa.gov/apod/ap980904.html ]. The Cassini spacecraft [ http://saturn.jpl.nasa.gov/cassini/english/spacecraft/ ] itself was about 10 million kilometers from Jupiter when recording the image data. |
|
Earth Rise
| Title |
Earth Rise |
| Explanation |
During the 1968 Christmas season Frank Borman, James Lovell, and William Anders flew the Apollo 8 [ http://www.ksc.nasa.gov/history/apollo/apollo-8/ apollo-8.html ] command module From the Earth to the Moon [ http://www.w3.org/hypertext/DataSources/bySubject/ Literature/Gutenberg/etext93/moon10.txt ] and back (launched Dec. 21, achieved 10 lunar orbits, landed Dec. 27). The Apollo 8 [ http://www.nasm.edu/APOLLO/AS08/Apollo8_fact.html ] mission's impressive list of firsts includes, the first manned flight using the Saturn V rocket [ http://antwrp.gsfc.nasa.gov/apod/ap950829.html ], the first humans to journey to the Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap951128.html ], and the first to photograph the Earth from deep space [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ]. The famous picture above [ http://images.jsc.nasa.gov/images/pao/AS8/10074963.htm ], showing the Earth rising above the Moon's limb as seen from lunar orbit, was a marvelous gift to the world. This was astronaut James Lovell's third mission. His last flight would be as commander of Apollo 13 [ http://antwrp.gsfc.nasa.gov/apod/ap950708.html ]. |
|
Stereo Saturn
| Title |
Stereo Saturn |
| Explanation |
Get out your red/blue glasses [ http://mpfwww.jpl.nasa.gov/MPF/mpf/glasses.html ] and launch [ http://beacon.jpl.nasa.gov/exhibits/voyager/ default.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://nssdc.gsfc.nasa.gov/database/ MasterCatalog?sc=1977-076A ] during its visit to [ http://sse.jpl.nasa.gov/missions/sat_missns/ sat-voy2.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. |
|
Voyager Views Titan's Haze
| Title |
Voyager Views Titan's Haze |
| Explanation |
Launched in 1977, 25 years ago [ http://voyager.jpl.nasa.gov/science/ planetary.html ] today, the Voyager 1 [ http://nssdc.gsfc.nasa.gov/database/ MasterCatalog?sc=1977-084A ] spacecraft's historic tour of the outer Solar System took it past Saturn in late 1980. On November 12, 1980, Voyager 1 recorded this view [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA01533 ] looking across the edge of Titan [ http://seds.lpl.arizona.edu/nineplanets/ nineplanets/titan.html ], Saturn's largest moon, from a distance of about 22,000 kilometers. Seen in false color, the moon's [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ] hazy atmosphere [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02238 ] appears orange with further layers of blue haze suspended above. Titan's mostly nitrogen atmosphere, denser than planet Earth's, also contains methane [ http://antwrp.gsfc.nasa.gov/apod/ap020212.html ] and is thought to be laced with more complex hydrogen and carbon compounds. The composition is likened [ http://www.lifeinuniverse.org/noflash/ Titanstate-06-02-01-01.html ] to Earth's atmosphere before life began. Spotted by Voyager [ http://voyager.jpl.nasa.gov/science/ saturn_titan.html ], the detached layers of haze hundreds of kilometers above the surface, along with details of Titan's atmospheric chemistry, have intrigued earth-bound researchers [ http://amesnews.arc.nasa.gov/releases/2002/ 02_93AR.html ] who have recently proposed a model that links seasonal variations in the haze, winds, and sunlight. Their model accounts for [ http://skyandtelescope.com/news/current/ article_716_1.asp ] the early Voyager observations as well as subsequent studies [ http://www.lpl.arizona.edu/~lemmon/titan/ ]. Further tests of the model are anticipated when the Huygens probe [ http://saturn.jpl.nasa.gov/cassini/english/spacecraft/ probe.shtml ], carried by the saturn-bound [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] Cassini spacecraft, enters Titan's atmosphere in 2005. |
|
Cassini Approaches Saturn
| Title |
Cassini Approaches Saturn |
| Explanation |
Cassini, a robot spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/index.cfm ] launched [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] in 1997 by NASA [ http://www.nasa.gov/ ], is close enough now to resolve many rings [ http://antwrp.gsfc.nasa.gov/apod/ap020215.html ] and moons [ http://mars.sgi.com/worlds/CyberMarz/Saturn/HTML/saturnMoons.html ] of its destination planet: Saturn [ http://www.nineplanets.org/saturn.html ]. The spacecraft has closed to about two Earth-Sun separations [ http://einstein.stcloudstate.edu/Dome/constellns/au.html ] from the ringed giant [ http://antwrp.gsfc.nasa.gov/apod/ap011223.html ]. Last month, Cassini [ http://saturn.jpl.nasa.gov/overview/index.cfm ] snapped several images during an engineering test. These images have been combined into the contrast-enhanced color composite pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA02884 ]. Saturn's rings and cloud-tops [ http://antwrp.gsfc.nasa.gov/apod/ap960317.html ] are visible on the far right, while Titan [ http://www.solarviews.com/eng/titan.htm ], its largest moon, is visible as the speck on the lower left. When arriving at Saturn in July 2004, the Cassini orbiter [ http://saturn.jpl.nasa.gov/overview/mission.cfm ] will begin to circle and study the Saturnian system. Several months later, a probe named Huygens [ http://saturn.jpl.nasa.gov/overview/huygens-probe.cfm ] will separate and attempt to land on the surface of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap020905.html ]. |
|
Jupiter, Io and Shadow
| Title |
Jupiter, Io and Shadow |
| Explanation |
Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02860 ] is the innermost of Jupiter's Galilean satellites [ http://www.jpl.nasa.gov/galileo/ganymede/ discovery.html ], Io, superposed in front of the gas giant planet. To the left of Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] is a dark spot that is Io's own shadow. A solar eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap021206.html ] would be seen from within the shadow spot on Jupiter. Viewed from [ http://space.jpl.nasa.gov ] planet Earth, similar shadows of Jupiter's large moons can often be seen crossing [ http://antwrp.gsfc.nasa.gov/apod/ap980202.html ] the giant planet's disk. But during the next several months, the Galilean moons can also be seen crossing in front of each other [ http://skyandtelescope.com/observing/objects/planets/ article_771_1.asp ] as, for a while, their orbits lie nearly edge-on when viewed [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=105&vbody=3&month=12&day=20¢ury=20&decade=0&year=2&hour=21&minute=35&rfov=30&fovmul=-1&bfov=30 ] by earthbound observers. This true-color contrast-enhanced image was taken [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] two years ago by the robot spacecraft Cassini, as it passed Jupiter on its way [ http://antwrp.gsfc.nasa.gov/apod/ap021104.html ] to Saturn in 2004. |
|
Orion Rising
| Title |
Orion Rising |
| Explanation |
Orion always comes up sideways [ http://www.internal.org/view_poem.phtml?poemID=137 ] ... and was caught in the act earlier this month by astronomer Jimmy Westlake, stargazing eastward over the Rocky Mountains north of Leadville, Colorado, USA. To make this gorgeous image, Westlake placed his camera on a tripod for two exposures. The first lasted for 18 minutes allowing the stars to trail [ http://antwrp.gsfc.nasa.gov/apod/ap021115.html ] as they rose above the mountain range. After a minute long pause, the second exposure began and lasted only 25 seconds decorating the end of each trail with a celestial point of light. The three bright stars in Orion's [ http://hou.lbl.gov/~vhoette/OrionNebula/ orion4.html ] belt stand in a nearly vertical line above the mountain peak right of center. Hanging from his belt, the stars and nebulae [ http://antwrp.gsfc.nasa.gov/apod/ap021220.html ] of the Hunter's sword follow the slope down and to the right. A festive yellow-orange Betelgeuse [ http://antwrp.gsfc.nasa.gov/apod/ap001222.html ] is the brightest star above the peak just left of center, but brighter still, planet Saturn shines near the upper left corner. In the foreground on planet Earth [ http://www.alanbeangallery.com/ homeward.html ], a frozen lake and snowy mountains are lit by a four day old crescent Moon. Happy Holidays and Best Wishes from APOD [ http://antwrp.gsfc.nasa.gov/apod/ap_faq.html ]! |
|
Happy Birthday Jules Verne
| Title |
Happy Birthday Jules Verne |
| Explanation |
One hundred seventy-five years ago (on February 8th), Jules Verne [ http://JV.Gilead.org.il/FAQ/index.html ] was born [ http://www.phys.uu.nl/~gdevries/verne/certificate.html ] in Nantes, France. Inspired by [ http://www.phys.uu.nl/~gdevries/verne/verne.html ] a lifelong fascination with machines, Verne wrote [ http://www.math.technion.ac.il/~rl/JulesVerne/works.html ] visionary works about "Extraordinary Voyages" including such terrestrial travels as Around the World in 80 Days [ http://www.fourmilab.ch/etexts/www/tdm80j/ ], Journey to the Centre of the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap021025.html ], and Twenty Thousand Leagues Under the Sea [ http://etext.lib.virginia.edu/toc/modeng/public/ VerTwen.html ]. In 1865 he published the story of three adventurers who undertook a journey From the Earth to the Moon [ http://vesuvius.jsc.nasa.gov/er/seh/index1.htm ]. Verne's characters rode a "projectile-vehicle" [ http://www.nasm.edu/galleries/gal113/ julesverne.jpg ] fired from a huge cannon constructed in Florida, USA. Does that sound vaguely familiar? A century later, the Saturn V rocket [ http://antwrp.gsfc.nasa.gov/apod/ap010525.html ] and NASA's Apollo program [ http://www.hq.nasa.gov/office/pao/History/Apollomon/ Apollo.html ] finally turned this work of fiction into fact, propelling adventuresome [ http://www.hq.nasa.gov/office/pao/History/SP-4214/ cover.html ] trios on what was perhaps Verne's most extraordinary voyage. This dramatic view [ http://www.hq.nasa.gov/office/pao/History/ap11ann/ kippsphotos/apollo.html ] shows the moonbound Apollo 11 space-vehicle riding top a Saturn V rocket as it blasts skyward. Launched from a spaceport [ http://www.ksc.nasa.gov/index.html ] in Florida, the Apollo 11 crew [ http://www.hq.nasa.gov/office/pao/History/ap11ann/ biographies.htm ] traveled to the moon and back again in 1969, making humanity's first landing on the lunar surface [ http://www.hq.nasa.gov/office/ pao/History/alsj/ ]. |
|
Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://www.nineplanets.org/mercury.html ]'s old surface is heavily cratered [ http://liftoff.msfc.nasa.gov/Academy/SPACE/SolarSystem/Meteors/Craters.html ] like many moons. Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap030216.html 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/ap000620.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap021104.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/ap010204.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/sun.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/ap010819.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/ap000320.html ], stop again, and then set quickly over the other horizon [ http://antwrp.gsfc.nasa.gov/apod/ap011209.html ]. From Earth, Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ] causes it to be visible only for a short time just after sunset or just before sunrise. |
|
Galileo Explores Europa
| Title |
Galileo Explores Europa |
| Explanation |
Details of the crazed cracks [ http://newproducts.jpl.nasa.gov/galileo/ganymede/p47183.html ] criss-crossing Europa's frozen surface [ http://antwrp.gsfc.nasa.gov/apod/ap960813.html ] are apparent in this mosaic of the Galileo spacecraft's latest images [ http://newproducts.jpl.nasa.gov/galileo/index.html ] of Jupiter's ice-covered moon. Curious white stripes, also seen by Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], are clearly visible marking the center of the wide dark fractures. One theory suggests that "dirty geysers" erupting along the cracks deposited darker material followed by a flow of cleaner water ice which produced the stripe. The above image [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1996/96-164.txt ] also shows an impact crater about 18.5 miles in diameter surrounded by white ejecta (lower left) and a curving x-pattern at bottom left which suggests fractures between icy plates filled with slush frozen in place. " Is there now or was there ever liquid water [ http://antwrp.gsfc.nasa.gov/apod/ap951118.html ] beneath Europa's surface [ http://antwrp.gsfc.nasa.gov/apod/ap960806.html ]? " These latest results still hold out that possibility -- and so the possibility of life. Europa, along with Mars [ http://antwrp.gsfc.nasa.gov/apod/ap960808.html ] and Saturn's moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap960716.html ] is considered to be one of the few places in our Solar System, beyond [ http://antwrp.gsfc.nasa.gov/apod/ap960701.html ] Earth, where primitive life forms could have developed. Galileo's close flyby of this tantalizing moon is scheduled for December [ http://newproducts.jpl.nasa.gov/galileo/background.html ] of this year. |
|
Farewell Jupiter
| Title |
Farewell Jupiter |
| Explanation |
Next stop: Saturn. The Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/ ], launched from Earth [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] in 1997, has now [ http://saturn.jpl.nasa.gov/operations/present-position.cfm ] swung past Jupiter [ http://www.jpl.nasa.gov/jupiterflyby/ ] and should arrive at Saturn [ http://www.nineplanets.org/saturn.html ] in the year 2004. Pictured to the left [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA03451 ] is a parting shot [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] from Cassini in 2001 January that would not have been possible from Earth: Jupiter showing a crescent phase [ http://antwrp.gsfc.nasa.gov/apod/ap010619.html ]. From the Earth and all points sunward of Jupiter [ http://www.nineplanets.org/jupiter.html ], the gas giant will always appear more fully lit than a crescent [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ]. Recent analysis of Jupiter images [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] taken from Cassini bolsters indications that clouds [ http://antwrp.gsfc.nasa.gov/apod/ap970920.html ] well up from below in the dark colored belts, not the light colored zones [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ], as believed previously. After arriving at Saturn, Cassini [ http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Cassini.html ] will decelerate to orbit [ http://saturn.jpl.nasa.gov/operations/saturn-arrival.cfm ] the ringed world and send a probe [ http://saturn.jpl.nasa.gov/operations/huygens-mission.cfm ] to its enigmatic moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html ]. |
|
Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/mercury.html ]'s old surface is heavily cratered [ http://antwrp.gsfc.nasa.gov/apod/ap950924.html ] like many moons. Mercury [ http://bang.lanl.gov/solarsys/mercury.htm ] is larger than most moons but smaller than Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap960717.html ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap950923.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/ap960819.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/ap960912.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/ap951114.html ], stop again, and then set quickly over the other horizon. From Earth [ http://antwrp.gsfc.nasa.gov/apod/ap951118.html ], Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960727.html ] cause it to be visible only for a short time [ http://www.maths.qmw.ac.uk/~lms/research/skyeye.html#planet ] just after sunset or just before sunrise. |
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