Quote:
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Originally Posted by Jerry
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Originally Posted by Celestial Mechanic
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Originally Posted by Jerry
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Originally Posted by Celestial Mechanic
Newtonian gravity does not predict a mass distribution--it observes one. Based on Kepler's 3rd law and centuries of observations we know the ratios of G*M of the planets and satellites to G*M of the Sun.
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Wrong! Because of Newton's postulate - the weak equivalence principle, we assume we know the mass of the Sun, and from the orbits of the moon's of the planets, and the perturbations of comets and probes, we predict the masses of the planets. Newton must be close, but we already know from the procession of Mercury's orbit, he is only close. |
Jessica H. Simpson on a mahogany crutch!  Don't you have any skills at reading for comprehension? I wrote that we know the ratios of G*M of the planets and satellites to G*M of the Sun, I did not write that we know the masses. I have bent over backward on this to accomodate your prattle and you still cannot get it right. The product G*M is what we know and all we need to know for Newtonian mechanics in the Solar System. |
I owe you a drink on this one. To first order, Newtonian mechanics are a given. What cannot be assumed is that at each orbital distance, the value of 'G' is equal to 'G' in the Earth - Moon orbit. In fact, if the Pioneer anomaly is not an artifact, the value of 'G' at earth orbit cannot be a cosmic constant. |
Jessica H. Simpson on a mahogany crutch with ivory inlays! You
still do not read for comprehension! Nowhere do I write about any particular value of G, at Earth orbit or otherwise. Say it with me one more time,
we know the ratios of G*M of the planets and satellites to G*M of the Sun.
If we assume G to be constant throughout the Solar System
and we perform a Cavendish experiment on Earth to determine G
and then combine that with the measured value of g on the surface of the Earth we can
infer the masses of the planets and satellites as seen in textbooks. But even if G is not constant it is not a total disaster for celestial mechanics because all we really need are the ratios of G*M for the planets and satellites to the ratio of G*M for the Sun. It does not matter what the actual value of G or M actually is, only the ratio of G(Saturn)*M(Saturn) to G(Sun)*M(Sun) is relevant. Got that?
You owe me a pitcher of margaritas for that one.
01-May-2005, 04:28 AM
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