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    Immutable firmament?
    From: Gary LaPook
    Date: 2010 Dec 3, 02:08 -0800

    While we were discussing the H.O. 2102-D I looked at having to periodically re-plott the stars as they move over time. To the ancients the heavens seemed immutable and constant and made out of the fifth element. But comparing the positions of the stars over a relatively short period of 25 years shows that they move considerably. I have attached excerpts from H.O. 249 volume 1 for epoch 1980 and epoch 2005 showing the positions of the stars and also examples of how much the altitudes of the stars will also change due to their motions. For example, looking at Capella, its SHA changes by 28 minutes and its altitude at 34 degrees north and LHA Aries of zero changes by 18 minutes. Most of the change in coordinates is due to the precession of the equinoxes.
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