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Heliocentric and Moon's motion

  1. Aug 17, 2010 #1
    Hello there!

    We know that in geocentric reference, Moon's trajectory is roughly a circle and moves at a mean speed of 3680km/hour.

    But, from a heliocentric frame of reference,
    Moon's trajectory in 1 sideral period isn't a circle but a curvature.

    [PLAIN]http://img22.imageshack.us/img22/6411/mmneg.jpg [Broken]

    Since Moon's circle orbit revolves around the Sun as the Moon revolves around our planet,
    Moon's speed from Sun's viewpoint may be different from 3680km/h.

    So, my question is:

    how long is this curvature in km? What's the MEAN speed of the Moon in heliocentric reference?

    Thank you
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Aug 17, 2010 #2


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    In one sidereal month, the Earth travels about 67 million km. The Moon's heliocentric path would be a approximately be a shallow sine wave 67 million km long and 768,000 km wide from peak to peak.( It would be some 87 times longer than the peak to peak thickness.)

    The mean heliocentric velocity would be equal to that of the Earth's orbital velocity, or ~30 km/sec.

    In addition, the curvature of the Moon's heliocentric path would always be towards the Sun.
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