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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction and humidity
From: Richard B. Langley
Date: 2007 Mar 28, 10:40 -0300
From: Richard B. Langley
Date: 2007 Mar 28, 10:40 -0300
Very thorough discussion on refraction: "Understanding Astronomical Refraction" by Andrew T. Young in The Observatory, Vol. 126, No. 1191, April 2006, pp. 82-115. -- Richard Langley On Wed, 28 Mar 2007, Alexandre E Eremenko wrote: > > >Bill, >The most advanced text on astronomical refraction >I have is the chapter of Chauvenet where he explains >the work of Bessel, and attaches tables computed by Bessel's >formula with refraction in fractions of a SECOND. >Bessel's formula does not take into account color or >humidity. Chauvenet says that Bessel's tables give >satisfactory results, and he does not mean observations >with a sextant to a fraction of a minute, but >he means real astronomical observations with instruments >of high precision. > >That's why I assume that color and humidity can be safely neglected >in the type of observations we do, as well as temperature and >pressure in most cases. > >Alex > >On Tue, 27 Mar 2007, Bill wrote: > >> >> >> Alex >> >> Following up on Sunday's conversation on refraction for star-to-star angular >> separation, the almanac states mean refraction is calculated for a >> temperature of 10C, pressure of 1010 mb, humidity of 80% and wavelength of >> 0.50169um. >> >> That would indicate my recollection that humidity is a component of >> refraction is correct, and my belief that the color of a star/body may >> affect refraction. I do not know if dust in the air will affect refraction >> like humidity. >> >> The important point in context is how much refraction will be affected, >> especially for lower bodies (20d to 30d). I don't have a clue. Perhaps the >> list can be of help. >> >> Bill >> >> >> >> >> >> > > > >> > =============================================================================== Richard B. Langley E-mail: lang@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ =============================================================================== --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---