The altitude angle (sometimes referred to as the "solar elevation angle") describes how high the sun appears in the sky. The angle is measured between an imaginary line between the observer and the sun and the horizontal plane the observer is standing on. The altitude angle is negative when the sun drops below the horizon. (In this graphic, replace "N" with "S" for observers in the Southern Hemisphere.)

The altitude angle is calculated as follows:

sin (Al) = [cos (L) * cos (D) * cos (H)] + [sin (L) * sin (D)]

where:

Al = Solar altitude angle

L = Latitude (negative for Southern Hemisphere)

D = Declination (negative for Southern Hemisphere)

H = Hour angle