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Frank,

I was specifically referring to recreating the correction table in the
lid of the sextant box.  Those are accurate to 5" or 10" of arc or 0.1'
of arc.  As you indicate, it might be tough to get that close,
especially without a high-powered telescope.

With my Husun "Mate," which has only a 2.5x "star" scope, I find I can
reliably get the index correction to within about 5" of arc with three
rounds of measurements of the sun's semi-diameter.  Superimposing stars
on one another is much tougher for me, and the results vary widely.

I did a few star-star distances, and some were quite strenuous.  My
more accurate distances, whether they be lunars or star-star shots,
have come when the sextant could be held in a more-or-less normal
position.  Below are the data I do have, pasted as a picture, so they
should look OK in the web archive.  Da1-2dd is the de-cleared angular
distance in decimal degrees and Da-Do" is the difference in seconds of
arc between the calculated and observed values.  Da1-2dd was de-cleared
for each observation within a set.

I got better as I went along.  But never replicated the precision and
accuracy of the Sirius-Procyon shots on 2/14.  I don't much believe
that the difference between the 2/14 shots and the second 2/23 shot was
measuring anything real having to do with the sextant.

Fred




On Jan 12, 2004, at 4:17 PM, Frank Reed wrote:

> Fred you wrote:
> "I mentioned star-star distance
> measurements to John Luykx of Navtrak Nauticals (he passed away last
> year, was a Pres of the navigation foundation, American) as a method of
> determining eccentricity and other "uncorrectable" sextant errors.
> John said he thought it might take upwards of 500 observations or sets
> of observations to assemble enough data.? It would be tough.?"
>
> Why do you suppose he thought that? Maybe he was wrong. Have you tried 
> star-star sights yourself?
>
> Another other nice thing about star-star sights is that they give us 
> information about the navigator's limits. If you do a series of these 
> on some specific pair of stars, and you end up with a scatter of 
> errors in the cleared distances, that scatter places a useful limit on 
> all other sextant observations you make.
>
> Frank E. Reed
> [X] Mystic, Connecticut
> [ ] Chicago, Illinois

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