NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Revisting refraction
From: Bill B
Date: 2005 May 13, 15:26 -0500
From: Bill B
Date: 2005 May 13, 15:26 -0500
While searching the list archives I came across an interesting posting by George Huxtable regarding refraction (re: refraction formula, Sept 28, 2000). Paul Hirose had posted the formula: R = 1 / tan (H + 7.31 / (H + 4.4)) R is refraction in minutes H is observed height in degrees (but was used as Hc by Paul) and George manipulated it as well as providing Saemundssen's Hc-to-observed formula--which was just what I needed. I noticed the 2005 Nautical Almanac provides a refraction formula similar to the one Paul posted in its sight reduction/direct computation section (page 280): Ro = 0.0167 / tan (H + 7.32 / (H + 4.32)) I believe I understand the 0.0167 vs. 1. The formula Paul posted gives refraction in minutes, while the almanac formula gives refraction in degrees (1/60 = 0.0167). I do not understand 7.31 vs. 7.32 or 4.4 vs. 4.32. Has the formula changed slightly over the years, or are there different camps on which (if any) is correct? My only thoughts are that the almanac formula goes on to correct Ro to R with a temperature/pressure-refraction correction, while no mention of temp/pressure correction is noted in the formula Paul posted. That reasoning does not pass my common-sense test. I would appreciate the list's views on the reason for the differences or which is more accurate. Thanks Bill