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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Buying a sextant- a cautionary tale.
From: Bill B
Date: 2006 Apr 30, 17:49 -0500
From: Bill B
Date: 2006 Apr 30, 17:49 -0500
Alex wrote > You can do the same with two stars at small distance if the > "off" part of your arc permits. The "off part" of my arc is > 5 degrees. So I can practice this method on any pair of stars > whose distance is less than 5 degrees. Yes, I saw that after my first post. The only difference here being that we are measuring the angular distance of the two limbs of the sun (diameter of the sun/body) on and off the arc, where with 1 pair of stars we are measuring their angular separation (much like a sun where known SD and 4SD helps us determine if our observations are close enough to be valued, we could use 2X the predicted separation as a sanity check). I will have to give that a try. To satisfy my curiosity, what was you IC with traditional sun and stars IE checks vs. your current IC using star pairs. If I recall about -0.2 with traditional methods and -0.7 with star to star? If we really want to get anal about it, for a one-star IE check we are using about the 0 point of the arc and worm gear, and for sun IE checks we are using points on and off the arc approx. 32' away from zero point and 32'/28' respectively on the worm gear. In our cases we have ruled out significant drum/worm gear eccentricity. That leaves us with a problem with the arc, which I suspect may be largely due to transfer of material from the softer worm gear to the arc. If we always do an equal number of clockwise and anti-clockwise checks that transfer should be uniform. If we always do our checks in one direction, wear and transfer will not be uniform, and all it took was an almost microscopic spore to shift my IE 1.'2 minutes on the Astra. Bill