[ATM] Calculating alt/az question

[David Weinshenker]

Shane LaPierre wrote:
> I am writing some SW to calculate the altitude of an object above the 
> observer's horizon.  I have been using this website to check the output 
> and am a little unclear on the math:
> http://www.stargazing.net/kepler/altaz.html
> 
> // the basic formula
> sin(ALT) = sin(DEC)*sin(LAT)+cos(DEC)*cos(LAT)*cos(HA)
> // the formula with my results
> sin(ALT) = 0.5943550 * 0.7933533 + 0.8042028 * 0.6087614 * 0.5823696
>          = 0.4715335 + 0.2851093
>          = 0.7566428
> 
> // formatted output - I assume this is a conversion of results from 
> above (0.7566428) to altitude in degrees
> ALT = 49.169122 degrees
> 
> I have arrived at the value 0.7566428.... but how to convert that to ALT 
> in degrees is my problem.  Any ideas?

The value calculated in that formula is sin(ALT) - the numerical value of
the sine of the angle. To get the angle in degrees, you need to take the
inverse sine (also known as arcsine or asin) of that value.

The calculator utility on my PC does in fact
confirm that asin(0.7566428) = 49.169122 degrees.

-dave w