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    Re: Question to Frank
    From: Frank Reed CT
    Date: 2005 Apr 27, 02:57 EDT

    Ken M wrote:
    "Perhaps another for latitude  might be included in the minimum making the
    number of sights equal to a lunar  taken with simultaneous altitudes of the
    Good point, and it  brings up something maybe interesting about a standard
    late 18th/early 19th  century lunar observation with simultaneous altitudes.
    Although they didn't  think of them that way at the time, we today can analyze
    these lunar  observations as ordinary line of position sights plus the lunar
    distance sight.  So you can get latitude and longitude out of them if the
    navigators have chosen  to record both altitudes. The altitudes give us two lines of
    position crossing  in a point --an ordinary fix-- and an error of the lunar
    distance of a minute of  arc simply shifts that fix east or west by about 30
    minutes of arc. This point  of view can be useful for analyzing historical lunar
    observations. I've got a  detailed lunar observation from 1809 where the
    navigator is in sight of land (he  has misidentified it but it is certainly the
    southernmost island of the  Maldives). He says he has taken his lunar observation
    about 3 leagues southeast  of the main body of the island and by analyzing
    the observation for both  latitude and longitude, it turns out that his
    observation was accurate to within  a few miles in both latitude and longitude. It's
    as exact as one could possibly  hope.
    42.0N 87.7W, or 41.4N  72.1W.

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