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.
