Compass Error from Amplitudes Observed on the Celestial Horizon
This calculation lists amplitudes of celestial bodies at rising and setting. Enter with the declination of the body and the latitude of the observer. The value derived is the amplitude when the center of the body is on the celestial horizon. For the sun, this occurs when the lower limb is a little more than half a diameter above the visible horizon. For the moon it occurs when the upper limb is about on the horizon.