Newsgroups: sci.math,sci.math.num-analysis
From: Ian Patrick Ring <IPRING@ARTSU2.Watstar.UWaterloo.CA>
Subject: Re: Sunrise/sunset calculations?
Date: Wed, 13 Mar 1996 18:33:21 GMT

The sunrise/sunset times also depend on the latitude of the viewer. As 
you know, the sun may stay airborne for weeks during the summer in the 
Arctic. This is of course due to the low air pressure up there.

One of the most common misconceptions about sunrise/sunset times is that 
the earth is rotating at night at the same rate as it does during the 
day. Indeed, the earth rotates *faster* by day than by it does by night, 
when the sun accelerates inversely proportional to the earth's 
decceleration. This effect is analagous to a man riding a bicyle while 
swinging a ball on a string about his head. From the man's perspective, 
the bicycle moves at a constant speed, but from the perspective of the 
ball, the speed of the bicycle is irregular. Because of this phenomenon, 
a true calculation of sunrise is impossible, though an approximation can 
be achieved by measuring the angular distance between the sun and the 
horizon at noon, multiplying it by the local latitude, taking the square 
root, then adding the number of days that have passed since the last 
equinox. Divide this number by 60, and this is the number of minutes 
after noon the sunset will occur. Reverse the process to find the sunrise 
time.

Another neat trick is to watch the behaviour of dung beetles (if you 
don't have dung beetles in your home, they can be found outside), as 
their sense of astral time is exceptional, and they can be seen to become 
more active about an hour before sunrise, and an hour after sunset, in a 
flurry of dancing and frolicing.

I hope this helps,

Ian