These files are here as an answer to questions frequently asked on sci.math, misc.consumers.house, and rec.gardens regarding solar position, solar power, sunrise/sunset times, etc.

I wrote up a description of the mathematics used. You might want to start with the announcement of the essay -- sort of a summary -- then move on to the document itself --- an ASCII description of the math model used. You should be aware of some corrections which were kindly forwarded to me by jbartlo@ouchem.chem.oakland.edu (Joseph Bartlo). You might prefer to read some other people's descriptions of the final formulae (it goes faster when you skip the derivation!). This includes references to algorithms and software; here's another example: sunrise -- (pointer, program) calculate it.

As an adjunct to this I wrote up a BASIC program to calculate sunrises and so on. If what you see in this sample output seems like what you want, then you should pick up the source code. It's actually written for a BASIC dialect I particularly like called UBASIC for the IBM-PC program. I have no connection with the UBASIC software (except as a satisfied customer). A primary source for this is the SimTel archives. While you're at SimTel you might as well check out the other ephemeris programs, such as this one.

Warning: references to times in my program are relative to "noon", meaning the moment each day when the sun is highest overhead. This is NOT 12:00 local time, largely because of the forced rounding into time zones. Moreover, it's NOT A CONSTANT for your locale: due to the ellipticity of earth's orbit (neglected in my model) the moment when the sun is highest overhead can vary (near my area it ranges from ~11:43 early November to ~12:14 late February).

Here are a couple of other posts of an astronomical nature which I thought to keep; I seem to have collected even more in a separate astronomy directory. (Note: this is just a little site by an amateur; don't expect much here...)

- A couple posts regarding the true shape of the earth" and its measurement.
- earth.shape2 -- how big is a minute of latitude at the equation?
- oblate.earth -- formulas for everyhing, assuming an oblate earth

For an internet "sunrise/sunset" server, try clarkson or the US Naval Observatory. (The latter has all the technical descriptions of 'sunrise' etc.)

The appropriate part of the sci.astro FAQ.

I have some information about spherical geometry and triangulation; some more general information about spheres (including coordinate systems) is available. Conceivably some other pointers to geometry could be useful.

Of course, the best description of the sunrise-time algorithms is here.

Other pages at my own web site you may find of interest:

- My home page is just a short introduction to the pages I maintain
- The parent page to this one is another short way-station, this time to a few pages concerning "applications" of mathematics (well, let's call them "investigations only a mathematician would love").
- I keep a large set of pages which provide a thematic introduction to the subject areas of modern mathematics, complete with answers to thousands of more or less common questions.

This page is

http://www.math.niu.edu/~rusin/papers/uses-math/position.sun/Last modified 2001/06/03 by Dave Rusin, rusin@math.niu.edu