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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
bodies."

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.

-FER
42.0N 87.7W, or 41.4N  72.1W.
www.HistoricalAtlas.com/lunars

   

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