NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dip
From: Frank Reed CT
Date: 2004 Dec 1, 00:42 EST
From: Frank Reed CT
Date: 2004 Dec 1, 00:42 EST
Alex E wrote:
"their main
conclusions seem to imply that the refraction
near the horizon (and thus the dip) is uncertain
to more than 1/2 of a degree."
conclusions seem to imply that the refraction
near the horizon (and thus the dip) is uncertain
to more than 1/2 of a degree."
Picture the Sun sitting on the horizon while you're standing on the deck of
a boat. Follow the lightrays back to the visible horizon and back to the limb of
the Sun. The lightray from the horizon you're seeing only has a short trip of a
few miles and it passes through only small changes in air density (under average
conditions). The lightray from the Sun's limb has the same path for the last
couple of miles but before that it has travelled all the way down through the
atmosphere (well beyond your visible horizon) and passed through a big gradient
in atmospheric density. That much longer trip yields lots or refraction and also
plenty of uncertainty in the net refraction.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
[ ] Mystic, Connecticut
[X] Chicago, Illinois
