How do we aim a satellite dish at a given satellite?

The aim is defined by two angles: azimuth and elevation, azimuth is the direction along the surface of the earth (north=0, south=PI/2, east=PI*3/4 or west=PI/4), elevation is the angle from the surface of the earth to the sky (0=along earth, PI/4=straight up).

The equations to give these angles are given below, can anyone tell me how to derive these?

azimuth = atan(tan(sat) - long/sin(lat)) * 57.296

elevation = atan(cos(f)-0.1512/sin(f)) * 57.296

where:

- f = acos(cos(sat)- long*cos(lat)) * 57.296
- lat = latitude of dish
- long = longtitude of dish
- sat =satellites orbital longtitude