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Re: Yes, I'm back

From:Christophe Grandsire <christophe.grandsire@...>
Date:Monday, January 20, 2003, 22:25
En réponse à Tim May <butsuri@...>:

> > No it doesn't. Kepler didn't know the mass of the sun. All Kepler's > third law states is that the periods of the planets are proportional > to the 3/2 powers of the major axis lengths of their orbits. You > can't relate that constant of proportionality to the mass of the sun > until you have Newton's law of gravitation.
And as soon as you have it you can. It doesn't mean that the relation changes so much that it cannot be called "Kepler's third law", it just means that we suddenly have a way to calculate the constant that Kepler couldn't himself. (Okay, you can still call
> the derived Newtonian version "Kepler's third law" if you like, but > Kepler never wrote it, and it's not what Peter was referring to.) >
By this kind of arguments, we shouldn't call Newton's laws of movement Newton's! Their current form has little to do with what Newton originally wrote. Yet the basis is still the same and the application too. It's the same for Kepler's third law. The fact that we can now derive the proportion constant doesn't mean the law has changed in any substantial way, or that we should make a difference between Kepler's third law as he originally wrote it and as we know it now. By Jove! It's only a matter of a constant that has become calculable! Christophe. Take your life as a movie: do not let anybody else play the leading role.


Tim May <butsuri@...>