The Explanatory Supplement to the Astronomical Almanac has several separate and extensive discussions on this topic, in particular section 9.33 in the 1992 edition, page 487. A small portion of the section is:
"At sunrise and sunset the apparent altitude of the upper limb on the horizon is zero and hence the adopted true altitude in degrees is h = -50/60 - .0353 * square roof of H where H is the height, in meters, of the observer above the horizon." Atmospheric refraction has so many uncertainties that making such a small adjustment is meaningless for practical purposes but it's an interesting mathematical exercise. From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Th. Taudin Chabot Sent: Wednesday, September 23, 2009 2:41 AM To: sund...@rrz.uni-koeln.de Subject: sunset/sunrise times All programs that calculate the sunrise/sunset times use an eye height of 0m. Many take the refraction in their calculations. But what is the effect of a normal eye height of 1.5 m when the observer is standing at sealevel like the beach. And when the eye height is even considerabel higher because the observationpoint is something like 300m above sealevel. Thibaud _____ Th. Taudin Chabot, . tcha...@dds.nl
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