NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: lat/long from meridian passage
From: George Huxtable
Date: 2011 Jan 26, 10:08 -0000
From: George Huxtable
Date: 2011 Jan 26, 10:08 -0000
Gary wrote- "A simple way to deal with the changing declination for determining LAN is to adjust your course to account for the movement of the sun." But (as he adds later) that is useful only for courses that are due East or West. In which case, isn't he adding an extra layer of complication that navigators would really be better-off forgetting about? He continued- "The sun changes declination fastest around the equinoxes and then it is only at the rate of one knot north or south. Right now the sun is moving north at a rate of 0.2 knots." No, the Sun has picked up Northerly speed since midwinter and right now is moving North at just over 0.6 knots. ================ All this complication demonstrates the futility of trying to obtain a precise longitude from Sun observations made anywhere near noon. Noon is the time for measuring latitude, as navigators have traditionally done throughout history. Longitude is best measured by Sun altitude observations taken well away from noon, in early morning or late afternoon, as navigators have traditionally done ever since longitude measurement became possible. George. contact George Huxtable, at george{at}hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.