Star date: 02:15:99
If you go outside any evening this week, look towards the western sky, and you will see a large bright, yellow point of light. This is the planet Saturn. Saturn was one of the seven "planets" known to ancient races of people. The others were Mercury, Venus, Mars and Jupiter. The Sun and Moon were also considered planets since they seemed to move in relation to the so called "background stars". Although it is only about 1/3 as massive as Jupiter, Saturn is 80% as large. This results in a situation where the density of Saturn is so low that if there were a body of water large enough, Saturn would float like a gigantic bathtub toy.
Saturn is best known for its magnificent system of rings. When Galileo first discovered the rings in the opening years of the 17th century, he believed they looked like a pair of ears encircling the planet. Christian Huygens later showed that the rings were, in fact, in the shape of a ring, encircling Saturn and at no point touching the planet. Today we know the rings to be not a single object, or even a few solid rings, but rather they are the collection of thousands of pebble to boulder size pieces of rock and dust. In fact, if they were one or more solid rings, they would quickly shatter into many separate pieces.
There are two reasons for this. The first reason is that the area inside the ring would be traveling faster the outside region. This is because the closer two bodies are to one another, the faster they revolve around each other. The second reason that solid rings could not hold together is because of tidal forces. The gravitational pull of Saturn on the insides of its ring system is greater than it's gravitational effect on the outer portions of it's rings. It is just such an effect caused by the Moon and the Sun on the Earth which creates the tides. Hence the name "tidal force".
Giovanni Cassini was the first person to spot a gap in the rings; the large gap which has since been known as the Cassini Division. The second largest gap in the rings is known as the Enke Division. The Cassini and the Enke divisions are not the only gaps in the rings, however. The rings of Saturn are actually composed of thousands of little tiny ringlets huddled together forming the appearance from Earth of a few giant rings.
When Voyagers 1 and 2 traveled out to this distant world, their cameras recorded images of the rings which resembled the grooves of a phonograph record. These thousands of ringlets are created and maintained by dozens or perhaps hundreds of small "shepard moons". With their gravity, these tiny moonlets constantly pull on the debris which makes up the rings, and corals them into thin ringlets encircling Saturn.
Saturn looks distinctly yellow when seen under clear skies. Look for it just 10 degrees south of west and about 25 degrees above the horizon at 8 p.m. all this week. It is one of the brightest lights in the sky, and is an easy find in a pair of binoculars or a telescope. Any size telescope can show evidence of the rings, although to see them clearly as even a few rings clearly separated from the planet takes a larger telescope, of about 6" diameter or better.
For all the beauty of it's intricate ring system, there is little detail to be seen when viewing the planet from the Earth with amateur level instruments. Yet, despite this, Saturn continues to be perhaps the most requested celestial sights at star parties. No one forgets their first view of Saturns rings, and when it is visible, it is often the topic of conversation for the amateur astronomers attending the star party.
Currently, there is a new space probe on its way to Saturn. The name of this robotic explorer is Cassini, named after Giovanni Cassini. This spacecraft will deploy a lander named Huygens which will land on the surface of Saturns largest moon, Titan.
Clear skies and good viewing.
"Understanding is joyous" - Carl Sagan
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