NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Lunar by altitudes
From: Bruce Stark
Date: 2002 Feb 26, 15:12 EST
From: Bruce Stark
Date: 2002 Feb 26, 15:12 EST
I just got signed on to the List, and probably shouldn't jump in so soon. The idea of comparing the altitude of the moon with that of one or more other bodies to get Greenwich time has been around almost continually for at least two centuries. It's such an appealing idea that many of the best navigation authorities have been blind-sided by it. First: Consider what you know about the reliable accuracy of altitudes taken from the sea horizon, especially from a small boat. You will be combining the errors of several such altitudes. Second: Consider what it is you are trying to do. You are trying to measure the moon's position in her orbit, NOT the rotation of the earth. If your latitude is less than 30� there may be times when you'll actually see the moon when her orbital motion is perpendicular to the horizon. At higher latitudes, never. The moon's is always within about 5� of the ecliptic. Her enlightened limb points to the sun and shows the path of her orbit. How often do you see the moon when her horns are pointing straight up or straight down? Bruce Stark