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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Easy Lunars in 1790
From: Alexandre Eremenko
Date: 2006 Apr 27, 21:16 -0400
From: Alexandre Eremenko
Date: 2006 Apr 27, 21:16 -0400
Ken, > I don't have those particular calculations > handy as they are at home So can you send them when you come home? I am not asking for any calculations, just the row data: DR coordinates, GMT and the distance, of YOUR observations not Thompson's. > So if Thompson had an almanac based on a better theory of the moon as well > as a calculator to clear his lunar more precisely, his longitude would > only have been off by 4" ;-) Well, this could happen only by coincidence, you cannot measure angles with any sextant consistently wo a fraction of a second. > (the posts are in the archives) we found that his standard deviation was > 20' (in longitude) using the old almanacs and would have been 14' if he > had the JPL data, so not bad but not great. That is 0.5' in the distance. This looks more plausible than 4". This I can also do from land with my sextant, almanac and calculator in good weather. > that he got this sextant in 1792 and there was much rough travel in the > interim (perhaps 30,000 miles by canoe, horseback, dogsled, and foot). > There are instances in his journals where his canoe is overturned in > whitewater and the sextant has to be fished out downstream. If you carry it in a proper box, you are unlikely to bend the frame. It will go out of adjustment, of course, but probably such an experienced person as Thompson would check and adjust his sextant before every observation. Thanks a lot, I will study the data you sent me. But you wrote that you tried to repeat his observations, and I am very curious to see the comparison of your results with his results. Alex.