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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant Positions versus Map Datums?
From: Bill Noyce
Date: 2002 Jan 18, 11:25 AM
From: Bill Noyce
Date: 2002 Jan 18, 11:25 AM
> He also goes on (p. 83) to give a formula for the difference between > geocentric latitude (assuming a spherical earth) and geographic > latitude (using the local vertical; what is plotted on charts). It > reaches a maximum of 11'32" at 45 degrees latitude. 11.5 miles sounds like a lot. Fortunately, a sextant measures using the local vertical, so it would give geographic latitude. The geocentric latitude would only be used for parallax measurements, as far as I can see. Bowditch gives a formula for adjusting the Moon's parallax based on latitude and (altitude or azimuth, can't remember), but it's quite small, as I recall.
