1. The problem statement, all variables and given/known data Hi everybody, I am trying to do a numerical aplication of change of coordinate system to another; the objective is to calculate the azimut of the sun knowing the altitude, hour angle and declination . 2. Relevant equations Cosh * Sina = Cosδ * Sin H where a is the azimut h is the altitude, in this case 27.5° δ is the declination, in this case 7.2° and H is the hour angle, in this case 10:00 on GTM+2; so 20h which is 300° 3. The attempt at a solution Sina = [ Cosδ * Sin H ] / CosH If I substitute the values, the azimut is -75.6°. The problem is that if I check the value of the azimut on the program stellarium for august 12 2014, the date from where the data has been chosen, the azimut is of 104º, and I don't know why there is such a difference between my azimut and the program's, Can anyone help please?