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Re: � � � Re: Lewis and Clark lunars: more 1803 Almanac data
From: Ken Muldrew
Date: 2004 Apr 22, 09:50 -0600
From: Ken Muldrew
Date: 2004 Apr 22, 09:50 -0600
On 21 Apr 2004 at 21:06, Bruce Stark wrote: > You may have found it, Ken. > > You wrote: "But it's just way too close to > the moon; 15?, in fact. Exactly 15?. Now I can't quite figure out what > error would lead to the captains recording distances that were off by > 15?, but for some reason the fact that there are no minutes or seconds > in the error makes me think it's possible." > > The vernier on Lewis's sextant read to 15" of arc, so I'm almost > certain the numbers on the arc would have been at 15? intervals. Also, > the index mark of the vernier was almost certainly near the right edge > of the "window frame" of the index arm. The 30? or 45? engraving they > should have been reading the additional degrees, minutes and seconds > from would have been outside the "window frame." Inside the frame, > where the serious reading was done, 60? would have appeared. I think this explanation is far more likely than my earlier thought that a magnitude 4.5 star was being mistaken for Aldebaran. There's a nice picture of just such a vernier given in the Mystic Seaport facsimile of Norie's Epitome. Frank Reed posted the URL about a week or two ago, but here's a link to the page in question: http://www.mysticseaport.org/library/initiative/ImPage.cfm?PageNum=2&B ibId=13617&ChapterId=28 (that all has to be on one line). > Perhaps, given the difficulty of reading a vernier sextant by > firelight, or candle lantern, they picked up on the 60?, and counted > from there. I can believe that. Especially given the common error of using the wrong minute when reading their watch. BTW, for anyone who would like to now try reducing their sights to a longitude, the position of Betelgeuse at that time is: RA: 5h 44m 34s Dec: 7? 21.5' Just subtract 15? from all the lunar distances in George's series A and C. \----------------------------+---------------------------------+ o_, O_/ \ Ken Muldrew, PhD | Voice: (403) 220-5976 | <\__/7 <\__ \ Dept. of Cell Biology | Fax: (403) 270-0617 | | / "\ L | University of Calgary | kmuldrew@acs.ucalgary.ca | / / < +-----------------------+---------------------------------+ / / Morning coffee recapitulate phylogeny L/