Compass Error from Amplitudes Observed on the Visible Horizon

This calculation contains a correction to be applied to the amplitude observed when the center of a celestial body is on the visible horizon, to obtain the corresponding amplitude when the center of the body is on the celestial horizon. For the sun, a planet, or a star, apply the correction in the direction away from the elevated pole, thus increasing the azimuth angle. For the moon apply half the correction toward the elevated pole.