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 ...."