You were right. There are lots of us on this mailing list. Sundial design and celestial navigation use the same math, spherical trigonometry.
The usual equation for altitude is: Sin Hc = Sin Lat X Sin Dec + Cos Lat X Cos Dec X Cos t. If you want azimuth: Sin Z = Sin t X Cos dec / Cos Hc. My reference is Bowdich, "American Practical Navigator" I've plugged these formulae into lots of programmable calculators. Once you have put the formula in once, the program is there, ready for use. I've had fun with the special case of this formula, when Hc = 0. Cos t = - Tan Lat / Tan Dec can be solved for the local time of sunrise and sunset (ignoring semidiameter and refraction). I will forward a letter posted earlier on this list. Roger Bailey Walking Shadow Designs At 08:07 PM 8/5/98 -0400, you wrote: >Sorry, I know I'm cheating. There's probably a celestial navigation list >and this belongs there, but... > >Can anyone tell me a formulae I can punch into a calculator to avoid sight >reduction tables and compute Hc directly? I used to have one, I think. > >My apologies to those of you who are only interested in sundials and not >navigation (although they ARE so similar even down to the careful drawing >of lines on paper that I doubt there are any offendees, anyway) > >jh > >
