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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 19, 21:05 EDT
From: Frank Reed CT
Date: 2005 Jun 19, 21:05 EDT
The other option (for getting shade error on a dense shade): Get a piece of good welder's glass or equivalent, dark enough to look at the Sun straight on. With no shades down, hold the welder's glass up to your eye and look through the sextant. Because of its location, optical imperfection in this glass will not matter. Now adjust the sextant for an ordinary IC test bringing the Sun's direct and reflected image into limb-to-limb contact. Lower the sextant, set aside the welder's glass, and swing in that dense shade. Whatever gap or overlap is now present between the direct and reflected Sun images is due entirely to the dense shade. Adjust it away and there's your shade error. If you're worried about holding the welder's glass in front of your eye where it might be heated by the focused light from the sextant's telescope, it also works fine if you hold it directly in front of the objective lense of the telescope. Does that all make sense? -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
