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B Question about Newton -- How did he know masses of various objects, like the Earth, Moon, Sun, etc.

  1. Mar 7, 2017 #1
    How did Newton estimate or know the masses of various objects, like the earth, moon, sun, etc., in order to check his equations? And how about the distances, say to the moon, and sun?

  2. jcsd
  3. Mar 7, 2017 #2


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    Staff: Mentor

    Niklas Koppernigk 1473 - 1543
    Johannes Kepler 1571 - 1630
    Issac Newton 1643 -1727
    Science never takes place in a vacuum. There have been scientists before and there will be after. In this special case, e.g. Kepler's laws have already been know.
  4. Mar 7, 2017 #3


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    He didn't know the masses. Nobody knew these values until Henry Cavendish performed the Cavendish Experiment and measured the value of G in about 1797, more than 50 years after Newton died. Before that, only the product GM was known. This is why the Cavendish Experiment is sometimes referred to as "weighing the Earth". The distances were known, at least approximately. Even the ancient Greeks had a decent estimate of the size of the Earth and the distances to the Sun and Moon.
  5. Mar 11, 2017 #4
    As long as the orbiting body is much less massive than the central body (e.g. the Moon about the Earth to a fair approximation; any planet about the sun) the size and shape of the orbit don't depend on how massive the lighter body is.
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