NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sextant calibration
From: Brad Morris
Date: 2013 Dec 17, 18:15 -0500
From: Brad Morris
Date: 2013 Dec 17, 18:15 -0500
Hi Alex
Its no secret that to appropriately calibrate to 0.1 arc minutes, the sensitivity of measurement should be an order of magnitude better. So as long as your sextant measurements are good to 0.6 arc seconds, you can calibrate your arc.
In review of Comdr Bauer's book, he indicates that his table of interstellar distances is for sextant practice and for calibrating. I have lots of respect for his knowledge and advice. He, too, must have been aware the in-exact nature of the calibration, since he treats refraction in such a cavalier fashion. Its as if he expects to only calibrate to within a few minutes of arc.
Brad
On Dec 17, 2013 6:07 PM, "Alexandre Eremenko" <eremenko@math.purdue.edu> wrote:
Brad, > Has anyone ever matched the results published on their certificate from a > calibration facility while using star to star distances? Open call: > Anyone? Exactly the same challenge was posted on this list more than 10 years ago (by Frank, if I remember correctly). To my knowledge nobody on this list ever claimed that s/he could do this. Alex. > Brad > On Dec 17, 2013 2:44 PM, "G Becker" wrote: > >> ------------------------------ >> >> I agree. When shooting Polaris in the daylight (not with a sextant) it >> reduces to a distinct tiny white pinpoint, it disappears behind the >> crosshairs. >> >> >> >> -----Original Message----- >> *From:* NavList@fer3.com [mailto:NavList@fer3.com] *On Behalf Of *Peter >> Monta >> *Sent:* Tuesday, December 17, 2013 2:10 PM >> *To:* george{at}gwbeckerpls.com >> *Subject:* [NavList] Re: Sextant calibration >> >> >> ------------------------------ >> >> Hi Brad, >> >> Rather than distinct points, stars are fuzzy blobs. >> >> >> >> It might help to illuminate the entire field with some background >> light---that way the overall contrast of the scene would be reduced, so >> that the eye would see just the bright cores of the stars against a grey >> background. Start with no light, acquire the blobs in the field of >> view, >> then gradually turn up the light source until the stars are maximally >> pointlike, but not so much that they're not easily trackable by eye as >> the >> sextant is swung and adjusted. >> >> The few times I've looked at Venus during the day with binoculars, I've >> been struck with how pointlike it seems against the blue sky. >> >> >> >> I have some camera images of star-star sights---they don't show the >> "fuzzy >> blobs" problem provided the exposure doesn't saturate the stars. At >> some >> point I hope to finish the job of estimating my sextant's arc error >> using >> these images. >> >> Cheers, >> Peter >> >> : http://fer3.com/arc/m2.aspx?i=125795 >> >> : http://fer3.com/arc/m2.aspx?i=125796 >> > > > : http://fer3.com/arc/m2.aspx?i=125798 > > > >
