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Re: circular orbits and other stuff



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Date: Fri, 20 Feb 1998 10:44:42 -0800
From: Leigh Palmer <palmer@sfu.ca>
Subject: Re: Circular orbits, and other stuff

I have another question for those who teach astronomy. The first
question (how is solar spinning angular momentum transferred to the
revolving planets via magnetic forces?) was not answered. I assume
it is not a simple topic.

It is not a simple topic, but it is sort of a nontopic.

The Sun has negligible angular momentum, so the question is
not really relevant to the solar system.

This is the present situation. According to nebular models, as stated by
Zeilik (chapter 12, 8th edition) the initial distribution of angular
momentum must have been just the opposite to what we now have. Just think
about the contracting cloud of gas (with a fixed spin) which becomes a
flat disk, more or less. The central part has the highest mass and the
largest share of angular momentum. As I am thinking about this again I
realize this is not at all obvious. But that is what the author wrote.
If the young solar system had a different distribution of angular
momentum than now then we do have an intersting topic. Zeilik claims
that the magnetic field can do the transferring.

How do elipticities change when the spin of our Sun is being
transferred to planets?

This question has to do with the fact that planetary orbits are
often nearly circular. The same is true for numerous moons and rings.
Kepler's laws would not be violated if eccentricities of planetary
orbits were very large. Why are most orbits nearly circular?

Tidal dissipation is strongest near periapse, and energy lost
near periapse tends to circularize an orbit.

I do not know anough about tidal dissipation to understand this sentence.
Can you elaborate? I assume I am not alone who does not know what the
periapse is. This word is not in Zeilik's glossary.
Ludwik Kowalski