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Re: Sextant precision
From: Alexandre Eremenko
Date: 2004 Oct 4, 00:05 -0500
From: Alexandre Eremenko
Date: 2004 Oct 4, 00:05 -0500
Dear Henry, I recently mentioned my attempts to measure the index error the way you describe, by comparing Sun's lower limb with its upper limb: (See my message on "star-to-star distances of Wed Sep 29 2004 - 16:02:05 EDT, paragraph 6). This was one of the three methods recommended by the manual to my SNO-T sextant. The other two were a) measuring the distance from a star to itself and b) the horizon method. After many repeated measurements I found the star-to-itself method more precise than the Sun method. This is the case with my sextant, my scopes and my specific observation conditions, I do not generalize this to all situations. (Unfortunately I have no possibility to use real horizon at this time). I can post the numerical data if this is interesting. However I don't know of any other method (other than star-to-star distances) of measuring what you call "centering error" without special equipment. This should answer your sentences: > Unless I have misunderstood the intent, > the purpose thereof, > however, from a purely navigational point of view, > appears somewhat > elusive. and >Interstellar distances, to the best of my somewhat >antiquated knowledge, >were considered a second line method of determining centering error, You say that the better method was: > At one time, an instrument > could be sent off for testing by a system of > collimators, But I don't have a collimator. And many other people don't. Bougainville :-) who used the stars for a similar test, as described in the recent messages: Fri Oct 01 2004 - 00:42:16 EDT and Fri Oct 01 2004 - 10:58:55 EDT Alex.