NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar Distance in Wikipedia
From: George Huxtable
Date: 2007 Jul 23, 09:55 +0100
From: George Huxtable
Date: 2007 Jul 23, 09:55 +0100
I had quoted the Wikipedia entry on Lunar Distance (Navigation) as- "[edit] Theory If there are two people, one at Greenwich and one 15 degrees West, the time by the sun will be one hour later at 15 degrees West. So, if the person observes the position of the moon at Greenwich at noon and another person observes the moon 15 degrees west of Greenwich at their locally determined noon, then due to the one hour difference, although the sun is at its zenith, the moon would have moved approximately its own diameter across the sky." and Frank replied- | The explanation as it stands is not literally incorrect. It's just | muddled and confusing. What that author is saying is that if I measure | the Sun-Moon lunar distance at my local noon, and another observer, | who by design is 15 degrees in longitude west of me, measures the Sun- | Moon lunar distance at his local noon, then because local noon occurs | an hour later, the Sun-Moon lunar distance will have changed by about | half a degree (the cleared distance, that is). Response from George- It seems to me that it really is literally incorrect, and in more ways than one: not "just" muddled and confusing.. If the author had said what Frank says he was saying, then there would be no argument about it. But he didn't, though that may be what he intended to convey. There's no way in which the time-by-the-sun, at 15 degrees West, can possibly be one hour later than it is at Greenwich. An additional error, which I first missed, but which Frank avoids in his rewording, is the statement that "due to the one hour difference ... the moon would have moved approximately its own diameter across the sky". It doesn't, of course. Like every other body near the ecliptic, the Moon moves about 15 degrees "across the sky" in any hour. It's with respect to the Sun, and the (invisible) star background, that the Moon moves by approximately its own diameter. Thanks to Frank for pointing out the serious abuse of the word "zenith"; another point I had missed on first reading. Frank ended- "Some of the articles are | maintained by informal teams of experts, and their articles are | excellent. Some of the articles are barely maintained at all, and the | content can be amateurish." Well, what about that as a little project for NavList, then? As an "informal team", we may be in as good a position as anyone else to agree a better explanation, between us, than the one that is presently posted. Anyone like to offer a first shot, to be kicked around by the group? To be a Wikipedia entry for "Lunar Distance (navigation)", that goes in under the NavList name, to give it (and us) a bit of credibility. There may well be other material, in the context of navigation, to which we could make some contribution, between us. George. contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---