# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Refraction
From: Gary LaPook
Date: 2007 Nov 09, 02:09 -0800

```Gary LaPook writes:

Back in March there was a discussion of various formulas to use to
predict refraction. I have found some other formulas that may be more
precise. The U.S. Naval Observatory used to publish its "Almanac For
computers" but stopped it after 1991. That publication has several
formulas for refraction:

(1)     R' = cot(a + (7.31/(a + 4.4)))

(2)    R = R' - 0.06sin(14.7R' + 13)

R is in minutes and a is the observed altitude. "At sea level, with
air temperature of 10�C and pressure of 1010 mb, R' of eq. (1) is
accurate to 0.07' and R of eq. (2) is accurate to 0.015' for an
altitude range of 0� - 90�."

"For nonstandard conditions the following formula is accurate to about
0.2' for temperatures in the range of -20� to + 40� C and pressures of
970 - 1050 mb.

(3)   R = R'((P - 80)/930)/(1 + 8x10 ^ -5(R' + 39) T - 10)))

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```
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