[time-nuts] Sunrise, solar noon, sunset and the Equation of Time

Mark Sims holrum at hotmail.com
Wed Aug 31 23:47:07 EDT 2016

Actually the main factor of determining observed sunset/sunrise times vs calculated ones are temperature gradients of the local atmosphere rather than than the absolute temperature/humidity/pressure... sunset being more disturbed than sunrise.   Local effects of several minutes have been observed.   And once you get near the poles all bets are off.

How you define solar noon is also an issue.  Most people would say it is when the sun is highest in the sky,  but it is really when the sun crosses 180 degrees azimuth (0 degrees in the southern hemisphere).   The two different methods can be a couple of minutes apart.

The sun elevation angle changes very slowly near solar noon which makes finding the exact peak more error prone than the azimuth angle which changes quite rapidly.  Lady Heather uses the elevation angle near the equator (are you really in the northern or southern hemisphere?) and near the poles (longitude/azimuth gets fuzzy).  Azimuth angle is used everywhere else. 


> I would also say that variations in air pressure, humidity and
temperature will alter the atmospheric refraction and therefore the
actual rise and set times by up to approx. 20-30 seconds

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