NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Thomas Jefferson and Lunar Obs.
From: George Huxtable
Date: 2005 Mar 26, 23:36 +0000
From: George Huxtable
Date: 2005 Mar 26, 23:36 +0000
In my recent contribution on this topic, I wrote- "This method presumes that Moon GHA was tabulated with sufficient accuracy and at small enough time intervals. This wasn't really true for the early Nautical Almanacs; mine, for 1767, provides Moon GHA only to an accuracy of one arc-minute, and at 12 hour intervals. Contrast this with lunar distances, which were tabulated to the arc-second (even if such precision was largely illusory), and at 3-hour intervals. I don't have easy access to the almanacs from 1803, which are relevant to Lewis and Clark's expedition, but expect that some Nav-L reader can kindly advise me how precise the predictions for Moon GHA were then." I referred to the Moon and star motion in terms of hour angle and GHA, because that's a familiar concept to modern navigators. But of course when referring to predictions in early almanacs they were always in terms of Right Ascension, not GHA. Sorry about that confusion. The same question arises, for the Almanacs around 1803. How precisely was the Moon's Right Ascension tabulated, and at what time intervals? George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================