Owen Duffy wrote:
"Jerry Martes" wrote in
news:QFxTi.27907$DX.11271@trnddc06:


does not charge for his program. He is an amateur, interested in
providing good data, and I consider you to be a good critic.


Hi Jerry,

That is flattering, but undeserved I am sure.

There are a lot of calculators on the 'net for giving the Sun's position
at a place and time, and they use varying algorithms for more or less
accuracy.

The routines I used in the spreadsheet were unashamedly the work of some
one else, the chap who converted them to VBA and the original NOAA
javascript routines behind their page at
http://www.srrb.noaa.gov/highlights/sunrise/azel.html . I have accepted
they were good enough for my application, and they seemed quite close to
another navigator application that I have.



And, really, what precision do you need for pointing/plotting?

Presumably folks are looking at fairly wide beamwidths (so that the sun
size (1/2degree) is a small fraction of the beamwidth)
5 degrees?
1 degree?

Get into that 1 degree range and you need to start taking into account
stuff like the non-spherical earth, and stuff like the sun's apparent
diameter (which is different for radio and visible light, as well as
varying with the distance).

Heck, you might have to worry about whether your local gravity vector
(presumably what you used to set the elevation zero point) is
perpendicular to the geoid surface used for the look angle calculation.
And, whether your zero az is actually the same north as used in the look
calculation (as opposed to, say, aligned to Polaris at some arbitrary time)

(FWIW, the calculations behind the USNO page do take a lot of this stuff
into account)

Owen