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On Nov 20, 2007, at 12:46 PM, Ken Muldrew wrote:
>
> On 20 Nov 2007 at 12:30, Fred Hebard wrote:
>
>> Yes, for star-to-star distances, you have to correct for spherical
>> aberration when clearing the observed distance, just like the
>> moon.   It's
>> been tried.  The problem is getting a precise star-to-star
>> distances.  I
>> don't believe anybody claims to have solved that  problem.  The only
>> solution seems to be to take it to somebody who  has a calibrating
>> machine,
>> or roll your own if you have access to  tens or hundreds of
>> thousands of
>> dollars of optical equipment.
>
> A clever method for measuring micrometer eccentricity is described
> in a
> message from a couple of years ago here:
>
> http://fer3.com/arc/m2.aspx?i=026728&y=200512
>
> Ken Muldrew.

Yes, but that won't help with scale eccentricity or off-centering of
the pivot.

You can check to see whether the sextant frame looks to be perfectly
flat, not that you can do this easily to high precision.  A bent
frame is a clear indication of a sextant that won't read accurately.





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