NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dip
From: Dan Allen
Date: 2004 Nov 27, 17:13 -0700
From: Dan Allen
Date: 2004 Nov 27, 17:13 -0700
Many texts describe the large uncertainty of refraction near the horizon. There is no refraction straight overhead. In the middle altitudes it is small and predictable and that's where most sights are shot (or at local noon). Few sights in practice are shot of bodies at the horizon, and the large uncertainty in the dip is just one of the reasons for this. Dan -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Alexandre Eremenko Sent: Saturday, November 27, 2004 4:41 PM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: Dip Dear fellow list members, I recently found an atricle which seems very disturbing to me: "Refraction near the horizon" by Schaefer and Liller, Publ. Astr. Soc. Pacific. You can read the paper on http://www.math.purdue.edu/~eremenko/dip.pdf The main point of the article is that the refraction near the horizon (and thus the dip of the horizon) varies unpredictably and the variation is enormous. The authors do not discuss Cel Nav in this paper, their main concern is refuring "Archaeoastronomy". I don't care about Archaeoastronomy, but their main conclusions seem to imply that the refraction near the horizon (and thus the dip) is uncertain to more than 1/2 of a degree. Then how is traditional CelNav based on altitude measurements possible at all? Any comments? Alex.