Saturn

SATURN

NAME
God of agriculture or harvest (Greek: Cronus)
ABOUT SATURN
Saturn is the second largest planet. It's famous feature is it's
rings. All the Gas Giants (Jupiter, Saturn, Uranus, Neptune) have
rings but only Saturn's are easily visible. It, like Jupiter is
composed primarily of hydrogen and helium. The density
of Saturn is lower than any other planet. It must have a very
small rocky core. It's density is below that of water so it
would float (if you can find an ocean big enough to put it in).
It rotates in a little over 10 hours, slightly slower than
jupiter which is just under 10 hours. Both planets are slightly
flattened (not quite round) by the centrifugal force from the
speedy rotation.

The rings were first noticed by Galileo who drew Saturn as a
triple planet. It would be about another 50 years before they
were recognized as rings. There are many rings but the three
primary ones were called 'A' , 'B' , and 'C' . They are composed
of small dust and ice particles. Some of the pieces are as large
as a house. There are several gaps in the rings, the largest
being 'Cassini's Division' discovered in 1675 by G. D. Cassini.
It's not certain where the rings came from. The best guess is
that they formed from the breakup of small moons which
eventually scatters particles in it's orbital path. Saturn's
gravity and Saturn's other moon's gravity then play a role in
shaping their appearance.
DISCOVERY DATE
Antiquity
MOONS
Fifty-six as of 7/23/06. The largest is Titan, the only moon in the
solar system with a substantial atmosphere. It will be the
subject of the Cassini space due in 2004. The Cassini
spacecraft will orbit Saturn and launch a probe into Titan's
atmosphere. Titan is fascinating because it is rich with the
organic compounds that is the basis of life.

Another moon is Iapetus. It was a mystery. Astronomers on
earth noticed it always appeared brighter on one side of it's
orbit than the other. Voyager photos revealed it is black on
it's leading hemisphere and white on the other accounting
for the brightness variations seen from earth. The source
of the dark material may be the next moon out, Phoebe. When
hit by meteorites, the blasted material may spiral inward
toward Saturn, collecting on the leading face of the next
moon inward (Iapetus).
OBSERVING - NAKED EYE
Saturn is generally similar in brightness to the brighter
stars in the sky. It can be picked out from stars because
it twinkles much less. All the planets shine with a steadier
light than the stars.
OBSERVING - TELESCOPE
Saturn is one of the best sights in a telescope. Even a cheap
department store telescope will show the magnificent
rings. Cassini's Division is also well seen. Saturn's globe
shows fewer features than Jupiter. The planet is further
away and the contrasts are a lot weaker. Some of the
cloud belts can be seen in it's atmosphere. Fewer than
Jupiter and also more difficult. Occasionally bright spots
will appear like 'The Great White Spot' of several years ago.
As the planet moves around in it's orbit (29 years) it slowly
tilts through our line of sight. This causes the rings to
sometimes appear more in sight. Then twice in it's orbit
the rings will appear edge-on. (this aspect is shown below)

This computer simulation shows Saturn as it would appear from Iapetus, one of it's most distant moons. The time step is about 2 days explaining the stars apparent rapid movement. The stars of course are not moving. They just appear to, as Iapetus circles Saturn. Iapetus orbits Saturn in about 79 days (the length of the animation). From an observer on Iapetus, Saturn's disk would appear about four times the diameter of our moon in our sky. The rings would add still larger dimensions. Iapetus was chosen because it's orbit is inclined enough to see the rings. Other moons orbit in Saturn's plane, meaning the rings would mostly appear edge-on from an observer there.

This computer simulation shows Saturn's changing tilt with respect to Earth. These tilt changes can be followed in a small telescope over it's 29 year orbit. (It's a slow process).

A Hubble Space Telescope image of Saturn's northern hemisphere

A closeup of Saturn's rings from Voyager. The shadow of
the rings can be seen on the planet.

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