the term "a" in your formula is the Sun's apparent altitude in degrees (see Chapter 16 of Meuus's Astronomical Algorithms).
On Tue, Mar 16, 2010 at 12:27 PM, Thomas Steiner <[email protected]>wrote: > Hi all, > I am looking for a formula for refraction. > At http://www.sundialsoc.org.uk/glossary/equations/equations.htm ist says: > > 10. Sun’s refraction > Ro=1/ (tan(a+7.31/(a+4.4))) > Ro is the refraction in arcmins for a temperature of 10ºC and an > atmospheric pressure of 1010 mb. For other conditions, a multiplying > factor of 0.28P/T is required, where P is the pressure in mb and T is > the temperature in kelvins ( = temp in ºC + 273). > > but obviously refraction does also change with the sun's altitude. > Only for low altitudes there will be refraction. Do you have a simple > formula or source for this by hand? > Danke, > Thomas > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > >
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