Monday, April 30, 2012

Saturn

Many observers consider Saturn to be the most spectacular planet. Its magnificent rings, seen clearly with even small telescopes, provides Saturn a great for over other planets such as Jupiter with its clouds or Mars and its surface features. Saturn is the sixth planet in the solar system and is the furthest away from the sun that we can see with the naked eye.
For the ancients, Saturn was the seventh and last planet. The list included the sun and moon as planets and the Earth was not included. Uranus, though may be seen with the unaided eye was not considered to be a planet in ancient times since it is too faint and moves very slowly. For these reasons Saturn had the honor to be the last planet.
Saturn's movement is slow, completing its orbit around the sun every 30 years. To see Saturn movement in the sky you should watch it every two weeks. At this duration its movement will be noticeable. Currently (May 2012) Saturn is in Virgo near the bright star Spica. Using Spica as a reference fixed star will help to identify the slight movement of Saturn. Saturn is the second largest planet, however its mass is not high (relatively) and its density is only 0.7 (g/cm2) which means that Saturn will float in a very (very) big ocean just like wood.


General information on Saturn (from Wikipedia)
Saturn information
Saturn orbit
Mean distance from sun 1,426,725,413 km
(9.537,070,32 AU)
Orbit time 10,832.327 days (29.657296 years)
Axis tilt 2.488°
Number of moons 60 and some more which are not named yet
Physical attributes
Radius 60,268 Km
Surface area: ‎4.27×1010‎ Sq. KM
Mass: ‎5.6846×1026‎ Kg
Density: 0.6873 g/cm2
Gravity: 8.96 m/sec2,
or 0.914 g
Rotation period: 10 hours, 47 minutes, 6 second
Rotation speed: 9.87 Km/Sec (Equator)
Rotation Axis tilt: 26.73°
Escape velocity: 35.49 Km/sec
Atmosphere
Pressure: 140 K Pascal
Hydrogen More than-93%
Helium More than-5%
Methane 0.2%
Water vapor 0.1%
Ammonia 0.01%
Ethane 0.0005%

Saturn was one of the planets that Galileo watched with his telescope in 1610. Galileo's telescope was not sharp enough and Galileo did not see the rings very well. Galileo saw something like two ears, and that is how he draw it.
Saturn in a draw by Galileo
Saturn in a draw by Galileo
After some years the ears (rings) disappeared and then re-appeared. The reason for this is that the rings plane was parallel to the earth and although the rings are large, there thickness (height) is just about 10 meters. Look from a distance on a sheet of paper with its narrow thin edge toward you, and you will hardly see it. Turn the paper toward you and you will see it clearly. It is the same with the rings which becomes invisible when they face exactly toward earth. The cycle of the rings plane movement is 14 years. After some years Galileo draw the rings of Saturn again, in a way which is more similar to what we usually see.

Saturn in a draw by Galileo
Saturn in a draw by Galileo

Only when telescopes were improved the fine details of the rings were discovered. The origin of the rings is unknown but the best theory is that an old icy moon of Saturn was crashed to millions of small pieces. The real beauty of the rings was discovered only when Pioneer and then Voyager came close enough to Saturn during the late seventies and early eighties.

Saturn from Pioneer 11
Saturn from Pioneer 11. Credit: NASA
Voyager images were much better. The next photo from Voyager 2 taken 21 Million KM from Saturn and shows 3 of its moons.

Saturn from Voyager 2
Saturn from Voyager 2. Credit: Nasa

These days Cassini is orbiting Saturn sending even more amazing photos. We will dedicate Cassini a special article next week.

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