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Re: H. Hughes and son sextant pat 491
From: Brad Morris
Date: 2019 Dec 4, 11:08 -0500

Hi David

I agree. If you just want to check that your sextant is okay after dropping it, then Cmdr Bauer's star-to-star distances might be okay. Might not even need to correct for refraction. As long as the result is in the ball park, the sextant is likely okay.

With all of the uncertainties in CN, the accuracy and repeatability of your instrument is something that can be known. Sextant calibration is a topic of great interest to me. You correctly assessed that I had mixed star-to-star sextant calibration in with a crude sextant check. For all the talk, I have yet to see anyone complete star to star calibration and publish results.

Cmdr Bauer's table of star-to-star distances is fine for some of the purposes stated. You can assess if your sextant is ruined or generally usable. Practice? Depends upon what you are trying to achieve. How will the beginning student assess his/her results?

A long time ago, when I first picked up a sextant, I found Cmdr Bauer's book to be a good resource. It explained a lot of things to that rank beginner. I have fond memories of the book. As time went on, Navlist has exposed some errors. The history of CN is particularly weak.

Writing is actually very hard. The few pages that Lars, Robin and I produced on Worsley convinced me of that. Any author here will tell you that. Its easier to point out flaws in a tome than to create the tome. Cmdr Bauer's The Sextant Handbook has flaws. At least he created a book, not just criticized the work of others. My fond memories have been cracked. Servicing your sextant, however, remains a solid chapter, which is what Sam was after.

Brad

On Tue, Dec 3, 2019, 12:34 PM David Pike <NoReply_DavidPike@fer3.com> wrote:

Brad Morris you wrote: Cmdr Bauer's star to star distances are uncorrected for refraction. Consequently, they are of little value for the purpose be describes.
Brad
Cdr Bauer’s table, Appendix F in the second edition of his book, is accompanied by a page of explanation where he goes into the effects of refraction and how to minimise it. Moreover, the table itself is entitled ‘For Practice and Sextant Testing’, not ‘For Sextant Calibration’. It seems to me that a lot would depend upon the length of the line joining the two stars, its tilt, and how high in the sky it is. I don’t want to say more until I’ve tried it with a known 'good' sextant. Currently, I’m stuck with clear skies – too cold to go star gazing, a bit warmer – sky obscured, plus a whole load of light pollution from living near a major airport and having a benevolent Council intent upon leaving street lighting on all night. I think the result will depend the user’s attitude to celestial. If like me you’re delighted to get within a couple of miles, and anything less than a mile must be a fluke, then it’ll be OK. If you consider anything greater than a mile to be failure, then you probably need to look elsewhere. DaveP

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