NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Artificial Sights"
From: Bruce Stark
Date: 2003 Mar 20, 20:01 EST
From: Bruce Stark
Date: 2003 Mar 20, 20:01 EST
I gave up on getting to that Yahoo list a lot quicker than George did. I expect the observations being taken were "equal altitudes." You'll find an explanation of them in most any nineteenth century navigation manual. The idea was that by taking them at different times, preferably five or more days apart, you could find the chronometer's rate of gain or loss. If you were at a known longitude you got the error on Greenwich time also. Lewis and Clark took lots of these observations, and worked at least one on their own. A calculation has to be made to find the "equation of equal altitudes," to adjust for the sun's change of declination between morning and afternoon sessions. Some time back the Navigator's Newsletter published a paper of mine showing an equal altitudes observation the captains took, and worked, at their "Bald-pated Prairie" camp on the Missouri. You can work it yourself, if you like, to see if you get the same chronometer error they got. The necessary pages of the 1804 Nautical Almanac are there, as are tables for finding the equation of equal altitudes. No reason you can't use those tables with the present Almanac, and try the observation yourself. Bruce
