NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
A Lunar alternative?
From: Peter Fogg
Date: 2003 Oct 2, 15:59 +1000
From: Peter Fogg
Date: 2003 Oct 2, 15:59 +1000
In his book 'Along the Clipper Way' Francis Chichester includes the story of
how the ship 'Alert' found its way, with difficulty, around Cape Horn in
mid-winter sometime before 1840. He then muses about the difficulties of
observing and working a "lunar" then goes on:
"...and then suddenly thought of a simple solution which I will explain
briefly: make a simultaneous observation of the sun and the moon for
altitude when the moon is nearly east or west. From this compute a sun-moon
fix, using a guessed-at GMT. Now compute a second fix from the same
observation but using a GMT which differs from the first by half an hour or
an hour. Now establish the latitude by a meridian altitude of the sun or any
other body as it crosses the meridian. This observation does not require
accurate time. Now join the two sun-moon fixes and the point where the line
joining them, produced if necessary, cuts the known latitude must be the
correct longitude at the time of the observation. Knowing the longitude
enables you also to know the correct GMT at the time of the sun-moon fix.
I fear the accuracy of this method, which depends on the rate of
movement of the moon in its orbit, would be poor, but it could be a most
valuable observation ...."
