NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar Distances with Alex's SNO-T
From: Alexandre Eremenko
Date: 2006 Nov 1, 09:45 -0500
From: Alexandre Eremenko
Date: 2006 Nov 1, 09:45 -0500
Dear Frank, > If you have a large enough work area (a couple of > hundred feet) and a decent laser, it should be infallible. Unfortunately, I do not have large work area. > Actually, the correct horizon SD > at the time of the observation was 15.9 > (calculated from 27.27% of the HP --you should > always use a calculated SD when > doing lunars). Then you need to augment it for > altitude which gives 16.0 > minutes of arc. The result is then quite a bit closer, but yes, a little off --an > error of 0.14 minutes of arc in the Moon's diameter. Can you just write the formula? > Based on your similar observations you wrote: > "Now I derive from my data IC=0.7 which also seems absurd." > I checked my notes, and that was the IC of that sextant > last time I checked. But this implies that all my observations with this sextant are very much off. (Assuming that it always was 0.7. I adjusted it only once in the very beginning, removed the side error.) Including all test of the index from stars. Returing to my sextant, I always had IC about -.2 to -.4 during the two years I own it. If it really was closer to -0.7, this would explain most of my overshots with star distances. But then how could I be so badly wrong with IC all the time? Including Sun and stars. The reason why Moon test can be unrelibale is that we can never be sure that we use the edge of the Moon, rather than the edge of the shade. On the other hand, I realize that in the two examples we discuss, we both had overshots in 4SD, and confusing the edge with the edge of the shade would give undershot. All this seems very strange. > This is one of the simplest observations you can make > with a sextant. If > it doesn't work, what on Earth could explain the error?? Could you make Sun and Moon tests with my sextant on the same hour and compare? Or maybe a laser test? Alex. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---