Jack: You wrote:
*I have been trying to figure out how to plot the duration of daylight over *>* the course of the year as a function of latitude. (I would generate a *>* curve for each latitude I am interested in.)* *[endquote]* *You said to disregard physical effects such as atmospheric refraction (and solar semi-diameter?). That simplifies the formula.* *Where h is the number of equal sundial-hours before or after solar noon at sunrise or sunset; dec is declination, and Lat is latitude:* *cos h = - tan Lat * tan dec.* *Double h, and that's the sunlight duration for that day, the day corresponding to some particular value of dec, at some particular latitude Lat.* *And yes, _lots_ of people at this list know that. I'm not posting something new. But I just wanted to mention it because I haven't seen it in the answers so far.* *Michael Ossipoff*
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