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    Re: Moon's angular speed
    From: Frank Reed CT
    Date: 2005 Nov 22, 01:22 EST

    Ken Gebhart wrote:
    "Don't you mean 13.2? per  HOUR instead of per day?"
    I probably should have included a little more  preamble. I was refering to
    the rate of the Moon's angular motion among the  stars.
    For example, if I have the Moon's (geocentric) RA and Dec at 10pm  and it's
    RA and Dec at 11pm (or SHA and Dec), how far apart are those two  locations?
    It's obviously not a big deal to calculate that directly if I have  the almanac
    data, but the "little method" I described yields a very good result  with
    almost no calculation. The average change in an hour is 33' of arc. If I  know
    that the HP at the present moment is 56.0', which is 1 minute below the  average
    value of 57.0, that's a decrease of 1.75%. So I double that and get  3.5%. The
    Moon will be moving 3.5% slower than the average speed of 33.0' per  hour. In
    an hour, its position will have changed 31.8 minutes of  arc.
    42.0N 87.7W, or 41.4N  72.1W.

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