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Re: A question... many answers
Posted By: Howard, on host 209.86.15.147
Date: Sunday, April 7, 2002, at 17:31:53
In Reply To: A question... posted by Wes on Sunday, April 7, 2002, at 04:51:53:

> Is the earth's orbit stationary with respect to the other planets? All the planets have a pretty much eliptical orbit (at least that's what I've heard, and it would make sense), with the sun as one foci. This means that the second foci could be rotating around the sun (with respect to other planets). Is it? Whenever I see pictures of the solar system the elipses are all pretty lined up, so I was just wondering. There could be reasons for whether they do or don't line up, I'm just wondering which it is.

You could write a whole book about orbital motion in the solar system. In fact, a number of people have done just that. Check around in any university library.

Your question is general enough to require numerous answers. Planets orbit the sun in different planes, but most of them are only a few degrees apart. Pluto, as has been pointed out, has an orbit that is all out of whack. It is far more eliptical than the other planets and is tilted at a drastic angle. My memory wants to say something like 30 degrees from average, but I haven't looked it up lately. It's also true that Pluto spends a couple of decades of it's 248+ years orbit within the orbit of Neptune. The next time it does that is at least two centuries into the future. Planets close to the sun travel faster in their orbits and take less time to complete the round trip. Because planets move in orbits that are less than circular, their distance from the sun varies. At their apogee, they move slower and at their perogee they move faster. The planets have only a small effect on the orbits of other planets, but when they pass close to each other, they may stray slighty from their usual path. This is due to gravitational attraction. The sun, being many times larger than even the largest planets, and having a mass much greater than all the planets put together, has the strongest gravitational field. A good measure of its strength is that it controls Pluto's orbit at a distance of between 3 and 4 billion miles. That's billion with a "b."
Even beyond Pluto, there are comets that are under the control of the sun's gravity.

As far as the second foci of a planet's orbit is a concerned, yes, it will swing around the sun.

There is usually a little confusion about the length of time required to complete an orbit. That is because it is sometimes measured with respect to the sun and sometimes with respect to the background of stars. This also results in confusion about the period of a planet's rotation. The earth rotates on it's axis once in 24 hours with respect to the sun. But with respect to the background stars, it is a little less. This is called a siderial day. Trusting my memory on that, I think it is about three minutes shorter than a solar day.

And did you know that the sun also rotates on it's axis? It takes about 30 days. However the suns poles and equitorial regions don't rotate at the same speed. A ball of gas can do that where a solid object like the earth can't.

When men made that famous landing on the moon almost 33 years ago, I was certain that by now, people would have visited at least one other planet. I am greatly disappointed. I also expected that bigger, better explorations of the moon would continue into this century. Another major disappointment.
Howard

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