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Refraction formula
From: Paul Hirose
Date: 2000 Sep 25, 10:25 PM
From: Paul Hirose
Date: 2000 Sep 25, 10:25 PM
The tables I posted showing the effect of refraction on angular separation used the refraction values from the table in the Nautical Almanac. For some reason it never occurred to me that the Almanac would have a formula I could program into my calculator, but it does: R = 1 / tan (H + 7.31 / (H + 4.4)) H is the non-refracted altitude. R is the number of minutes to add to H to obtain apparent (refracted) altitude. The formula is for standard conditions of 10 degrees C and 1010 millibars. Be sure to observe correct order of arithmetic operations: divide 7.31 by (H + 4.4), then add H and take the tangent. Of course the formula is an approximation; note that refraction is not exactly zero at H = 90! I rewrote my calculator program to use this formula and recomputed my tables. The differences were trifling.
