NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Question to Frank
From: Frank Reed CT
Date: 2005 Apr 27, 02:57 EDT
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 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