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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.

   \----------------------------+---------------------------------+
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 O_/ \    Ken Muldrew, PhD      | Voice: (403) 220-5976           |
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 <\__  \  Dept. of Cell Biology | Fax:   (403) 270-0617           |
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