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    Re: Star to star angular measurement, beginner
    From: George Huxtable
    Date: 2005 Mar 12, 18:52 +0000

    >On Mar 11, 2005, at 11:16 PM, Frank Reed wrote:
    >> By the way, parallax, for the Moon, Sun etc. is also an entirely
    >> vertical correction so you can go immediately to the case of lunar
    >> distance calculations from you star-star calculations, if you want.
    >> There's one small issue: the Earth's oblateness yields a slightly
    >> non-vertical component to parallax but that can be dealt with
    >> separately.
    And Mark Bernstein asked-
    >This brings up the question: why is it called "horizontal parallax"?
    And the answer- Because it's the amount of parallax (in a vertical
    direction) that affects an object that's seen horizontally, on the horizon,
    at an altitude of zero degrees. At higher altitudes, the parallax varies as
    cos (alt), becoming zero for an object at the observer's zenith. whan the
    altitude is 90 degrees.
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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