NavList:
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 18, 22:20 EDT
From: Frank Reed CT
Date: 2005 Jun 18, 22:20 EDT
George H, you wrote: "one such shade on my sextant quite defeats any such attempts. It's the very darkest shade, a very deep-blue one in my case, that's required for viewing the sun. When I look through that shade, it's so dark that the only object I can see is the sun. Without that shade, I can't safely look at the sun at all. So how do I compare two measured angles, observed with and without that shade? What do I look at, to do that job? Others must have met that same problem. Suggestions, please." Yes, I know what you're talking about. What you need is something brighter than the Moon and fainter than the Sun. That's a big range: around 14 magnitudes or a factor of 400,000 in luminosity, so lots or possibilities... I have used the setting sun which is faint enough to look at comfortably with a medium shade and bright enough to see through a very dense shade --there is *some* altitude near the horizon where this should be possible. I've also used metal rooftops that are reflecting almost direct sunlight. You get an IC using the medium shade (whose shade error you've already determined with the Moon perhaps) and then you get an independent IC with the dense shade. A little arithmetic yields the shade error of the dense shade. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars