NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: lunars from Mt. Everest?
From: Ken Muldrew
Date: 2003 Dec 18, 09:43 -0700
From: Ken Muldrew
Date: 2003 Dec 18, 09:43 -0700
On 17 Dec 2003 at 21:09, Frank Reed wrote: > If you observe an object in the sky at an > altitude of 15 degrees, the sea level refraction is 3.6 minutes at sea > level, but in Denver it would be 3.1 minutes. That's not a big deal > for standard line of position sights, but it would be a major source > of error for land-based lunars practice. I would guess that many locations at high altitude are also going to be in mountainous country where the lunar stars might be just above the raised horizon of a mountain. In such cases the refraction due to temperature changes will probably be signficant (at least, the stars twinkle a lot when they're close to the mountain (in an angular sense)). I wonder what the minimum angle is that one could get away with before the error becomes intolerable. Is refraction a big problem for navigation at sea when sighting the horizon? The celebrated land-based navigator David Thompson used temperature and altitude to correct for refraction. His altitudes came from occasional boiling-point measurements and estimated reckoning. They were sometimes out by several thousand feet (although they were usually better than that). \----------------------------+---------------------------------+ o_, O_/ \ Ken Muldrew, PhD | Voice: (403) 220-5976 | <\__/7 <\__ \ Dept. of Cell Biology | Fax: (403) 270-0617 | | / "\ L | University of Calgary | kmuldrew@acs.ucalgary.ca | / / < +-----------------------+---------------------------------+ / / Morning coffee recapitulate phylogeny L/