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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar altitudes
From: George Huxtable
Date: 2003 Apr 17, 06:38 +0100
From: George Huxtable
Date: 2003 Apr 17, 06:38 +0100
Fred Hebard said, about the plot of land-based lunar distances, from the 1850s, that I recently posted- > Also, since George had bragged about the >data being so good, I assume that his data point at 22h 39m 00s 29d 43' >50" was a typo, where the 43' should have been 45', and changed that >point accordingly. Fred deduced my error correctly. Sorry about the typo. ======================= On a separate matter altogether, Jan Kalivoda asked a sensible question, under this thread on lunar altitudes, a few days ago, as follows- >The method of lunar altitudes for finding the GMT seems ideal to me for >the observation above an artificial horizon (ashore, of course). The >problems with dip, with the blurred sea horizon, with the short period of >twighlight would then disappear completely. With an artificial horizon one >can wait through the whole night, until the Moon with a star (not very >distant from the Moon, but their azimuths don't matter too much in this >case) come to the prime vertical. Many occasions can arise through the >month and one could expect better results than with lunar distances, isn't >it? . This could be very important in early days, when the knowledge of >the accurate longitude was an exception outside the Europe and USA (maybe >Caribbean) and the method of combining local time and longitude to obtain >the GMT was therefore unavailable in remote countries. > >Had you anybody heard anything about such usage? I didn't. > >Maybe somebody from the list, who is in possession of a sextant and an >artificial horizon, can try this method? It cannot be too difficult, I >guess (from the desktop). ======================= Because I hadn't read Jan's question carefully enough, my response was completely irrelevant, referring to lunar-distance measurements rather than lunar-altitudes. So once again, sorry about that. I agree that the methods proposed by Chichester and others, using lunar altitudes rather than lunar distances, would have been more appropriate for on-land measurements using a reflecting liquid than they would for sea measurements using the horizon. But like Jan, I have seen no account of such a method in use on land. George Huxtable. ================================================================ 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. ================================================================