Re: Nodal regression

From: Thomas Fly (
Date: Thu Dec 04 2003 - 14:48:51 EST

  • Next message: Thomas Fly: "Re: ISS occulting.../precession"

    Robert Matson wrote:
    > On the subject of orbital precession (i.e. nodal regression) you asked:
    > > So, what would account for such a huge precession of the plane of orbit?
    > The earth's equatorial bulge.
    Yeah, I just realized that a minute ago.
    Just as a charged sphere "looks like" a point charge at its center from outside
    the sphere, a spherical object "looks like" a point mass at the center only when
    its density depends solely upon the distance from the center.
    Because of the earth's rotation, it more nearly resembles such a sphere, but
    with a huge mountain range encircling the equator. As the ISS approaches the
    equator from the north, it's deflected downloads (toward the south); as it's
    pulling away from the equator, it's deflected upwards (it's once again deflected
    as it crosses the equator from south to north). The situation is similar to a
    ray of light being slightly shifted in position as it passes at an angle through
    a plate of glass.
    So, as you note, all satellites (except those in an equatorial or polar orbit)
    would be affected; the degree would depend upon their altitude (so Hubble, in a
    higher orbit, would be less deflected).
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