Re: Sextant Positions versus Map Datums?
Subject: Re: Sextant Positions versus Map Datums?
From: Noyce, Bill (William.Noyce@XXX.XXX)
Date: Fri Jan 18 2002 - 13:25:05 EST
> 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.
