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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: sextant precision.
From: Frank Reed CT
Date: 2005 Jun 22, 06:29 EDT
From: Frank Reed CT
Date: 2005 Jun 22, 06:29 EDT
Bill you wrote: "My contention is that a optically perfect shade with faces parallel will still offset the ray if not perfectly perpendicular to the ray path. You are probably correct that the offset is negligible in practice, but nonetheless does exist." So experiment! Get a piece of flat clear glass, and hold it in the light path. Rotate it. Tilt it 45 degrees to the light path. Then try perpendicular to the rays. Does it change the alignment of direct and reflected images in your sextant? There's nothing like experimental evidence to constrain one's theoretical musings. Here's another: No sextant involved. Hold a piece of flat glass close to some text on a page at normal reading distance. Rotate it. Does the text appear to shift from refraction (it should)? Now hold that same piece of flat glass up in front of some distant scenery. When you rotate the glass as before, do objects shift back and forth (they shouldn't)? TRY this experiment and see if you agree with my should/shouldn't comments. Then work out the theory... Evidence constrains theory. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
