Galilean Project Four: Saturn

Galilean Project Four: Saturn

INTRODUCTION. In this Galilean exercise, you yourself will see Galileo's fourth rebuttal to the popular knowledge which said that all things in the universe revolve around the earth.

Even with a very low power telescope or binoculars (that's all Galileo had!) you have seen that Jupiter was more than a pin-prick of light - it was discernably a very small disk. (Hint: the sun is the only star that you will see that is a disk and not just a point of light. (Even with the most powerful land-based telescopes, the next nearest star appears to be just a point of light.) Well-, Saturn (as well as Venus, Mars and Jupiter!) can be seen as something more than a point of light. Indeed, Saturn is really a different delight to see: often it looks like a hard-boiled egg sitting in the middle of a saucer. Saturn's rings are usually very visible (except when they are seen from edge-on). We now know that the rings are composed of small gravels - each one a moon of sorts - but a very small moon. Thus the rings are zillions of moonlets whirling around the main planet. So, while each one is very small, there are so many of them that you can see them - unlike Saturn's larger moons which are so far away in dim sunlight that you cannot see them unless you have a BIG telescope.

Observations of Saturn can be directed at several diffent questions:

Is Saturn "interior" or "exterior" to earth's orbit around the sun?
How is Saturn's orbital plane situated relative to earth's orbital plane?
How are the rings' orbital planes situated relative to Saturn's orbital plane?
How is Saturn's axis oriented relative to its orbital plane?

Question #1: After having gone through the earlier Galilean proofs, you should be well set up to tackle question #1, and should have developed a few "tricks of the trade." You go out in an evening in which Saturn is in the sky. (Saturn is shining only half of the year for reasons you will determine during the course of your observations.) As you stand there, try to imagine where the sun is at that time. If it is about 9 p.m. in the winter, you will be pointing downwards at about 45 degrees in a westward direction. Now you ask if Saturn is in the eastern or western part of the sky. If it is in the eastern sky, it means it MUST be which of the following: close to the sun than we are, or further away? However, you might not be so lucky and you see Saturn in the western part of the sky. The trick you know is to "scope" it to see if it is a crescent or not. And if you see a crescent nestled within the rings, then it MUST be closer or further from the sun than you and your earth platform are? But you might be very unlucky and see Saturn in the western sky as a round disk! Already you have determined using a soccerball Venus in your darkened room with a lightbulb, that a closer planet can appear as a disk, just as can a exterior planet. So what to do? Just be patient and wait three months and then see what you see. What will have happened is that (mostly) the earth has moved to a different position around the sun.

Question #2: This you might have already ascertained if you had previously determined the shape of the solar system. If you haven't done that, you should go back and do that and within that project is included looking at Saturn's orbital plane relative to the positions of the orbital planes of the other planets including that of earth.
Question #3: The answer as to the position of the rings' orbital plane with that of the earth's orbit, is USUALLY an absurdly simple question. If you can see the rings, their plane must be tilted from your plane in order for you to see them. But you happen to be one of the most unlucky persons in the world, and you don't see any rings at all (making it very hard indeed for you to distinguish Saturn from Jupiter - but Jupiter has visible moons using low power). It may just happen that Jupiter is in a position that you are looking at the rings edge-on, and because they are whispy-thin, you see nothing. Sort of like trying to see a piece of paper edge-on from way down your street (but it easily seen if held at right angles to your line of sight). It should be interesting to note that the rings' plane remains constant no matter where Saturn is in its orbit (or stating it in other words: no matter what time of Saturn's year it is). This is shown as a series of pictures at the right.
Question #4: Most students will have to forego answering this project as they will not possess a powerful enough telescope to see the cloud bands on Saturn's surface.

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In summary, by doing the projects on this page you will have shown that both Saturn itself must revolve around the sun and not the earth, and that the constancy of the orientation of the rings supports that conclusion. Thus Galileo put forth his fourth proof.