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    Re: A lunar in 1845
    From: Ed Popko
    Date: 2019 Jan 2, 03:47 -0800

    Frank,

    Reading these old log book is an art. It's not likely I got this right:

    633. Tuesday May 13, 1845
    Latt by Obs 26 deg 50 min N
    Long by Lunar 67 deg 30 min W


    634. Wednesday May 14, 1845
    Latt by Obs 20 degree 57 min N
    Long by Chron 68 deg 20 min W

    By the way, what are the numbers 633 and 634? Just numer of entry or could it mean consecutive day at sea?



    Assuming the log entries are made at about the same time each day, could the ship have advanced about 356 nautical miles in one day? I made a mistake somewhere in reading or in calculating the distance.

    But on the lunar estimation, the situation might be something like this:

    - the sight is approaching vertical sun-moon alignment
    - observer is inbetween the sun and moon's ground point and on a great circle through those points (or near so)
    - corner cosine correction for bodies is approaching zero as the sun-zenith-moon triangle collapses to a vertical line
    - lunar distance is almost totally the sun and moon semidiameters and moon's HP. Corner cosines effect becoming zero.
    - refraction estimates might be ignored
    - LDs approaching 90 degrees, moon's altitude is less important, less impact on actual clearing required accurcy of altitudes is less

    Ed

       
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