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 Mar. 10, 1999:
Since mid-February the western sky has been a showcase
of bright planets. On Feb. 23, Venus and Jupiter executed a
dazzling
conjunction seen by millions. Barely two weeks later
Mercury appeared from behind the sun and four planets -- Mercury, Venus, Jupiter, and Saturn --
were visible at the same time in the western sky.
The show is continuing this week, and this time the star, or rather the planet, is Saturn. Right: This rendering by artist Duane Hilton shows the relative positions of Venus and Saturn in the western sky soon after sunset this week. The mountains pictured are part of the Sierra Nevada range in central California. Saturn is visible to the naked eye soon after sunset. To find the ringed planet, it's easiest to "planet-hop" from Venus. Face west-southwest after the sun sets and look just above the horizon. Venus, at magnitude -4.0, will be impossible to miss. Venus is so bright that it is often mistaken for an airplane, but it does not blink or move so it should be easy to identify. Saturn is to the upper left of Venus, approximately 10 degrees away. At magnitude +0.5, it will be easily visible to the naked eye. |
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Saturn is widely regarded as the jewel of the night sky. It's not
the brightest planet as seen from Earth, but it rarely fails to evoke
a gasp of awe when seen through a telescope for the first time.
The reason, of course, is Saturn's spectacular system of rings
spanning over a half a million kilometers in
diameter.
This week Saturn offers an added bonus to sky watchers with access to a small telescope. From Wednesday, March, 10 through Friday March 12, Saturn's largest moon Titan will be visible about 4 ring-lengths west of the planet. |
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Left: An
image of cloud-covered Titan snapped by Voyager 1 when the spacecraft
visited Saturn in 1980. More information
Titan is one of the strangest places in the Solar System. It is larger than the planets Mercury and Pluto, and is one of only two moons known to have a substantial atmosphere (Neptune's moon Triton is the other). Although Titan has been photographed by spacecraft and Earth's most powerful telescopes, its cloud-covered surface remains a mystery. Titan's thick atmosphere is mostly nitrogen, like Earth's, but contains much higher percentages of chemicals such as methane and ethane. The "smog" may be so thick that it actually rains "gasoline-like" liquids. While Titan's surface is normally hidden from view, astronomers have succeeded in peering through the haze by observing Titan at near-infrared wavelengths with the Hubble Space Telescope. At infrared wavelengths, which are longer than visible light, Titan's smog-like atmosphere begins to be transparent enough to allow glimpses of its surface. The bright feature seen in the Hubble image below is about 2,500 miles across, similar in size to Australia. The bright and dark areas might represent oceans, continents, craters, or other features. There is much speculation, but no one knows. 
Right: In 1995
Peter Smith of the University of Arizona Lunar
and Planetary Laboratory and colleagues used the
Hubble Space Telescope to photograph Titan at infrared wavelengths.
They
mapped light and dark features over the surface of the
satellite during nearly a complete 16-day rotation. This image shows
a
prominent bright area they discovered about the size of the continent of
Australia. More information
Many basic questions about Titan may be answered by the Cassini mission, which was launched in 1997 for a rendevous with Saturn in 2004. Once in the Saturn system, the spacecraft will release the European Space Agency's Huygens Probe. The probe will drop into Titan's atmosphere and slowly descend to the surface by parachute. Onboard instruments will measure temperature, pressure, density and energy balance in the atmosphere throughout the descent. As the Huygens probe breaks through the cloud deck, a camera will capture pictures of the Titan panorama. Other instruments will directly measure the organic chemistry in Titan's atmosphere, which is thought to resemble that of early Earth. Instruments will also be used to study properties of Titan's surface remotely, and perhaps even directly if the probe survives the descent and landing. 
Left: An artist's concept of the Huygens Probe as it descends
toward the surface of Titan. Image credit: JPL. JPL Huygens Probe web site
Astronomers will undoubtedly continue their studies of Titan from afar, but Titan is likely to remain an enigma until Cassini reaches Saturn in 2004. For now, star gazers who see a tiny point of light west of Saturn's rings this week must rely on their own imaginations to provide the answers to the mysteries of Saturn's wondrous moon. |
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Cassini Mission web site -- from JPL
Hubble Telescope Photo of Titan -- HST infrared images of Titan, June 1995 Titan: Saturn's Smog Moon -- Astronomy Picture of the Day, Feb. 7, 1999 A glimpse of Titan's surface -- Astronomy Picture of the Day, Oct. 21, 1995 This week's sky at a glance -- from Sky & Telescope The Nine Planets: Saturn -- from SEDS The Nine Planets: Titan -- from SEDS The Solar System Photo Gallery -- from the National Space Science Data Center More NASA Space Science News |
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