In open seas, heavenly bodies are used to determine the compass error. Watch keepers must calculate compass error at least once every watch and after every major alteration of course. Azimuth is also used when calculating sights to obtain the position line of the heavenly body.
The azimuth of a heavenly body is defined as the angle at the observer’s zenith or the arc of his rational horizon, contained between his celestial meridian and the vertical circle through the body.
Looking at the figure NESW- is the celestial sphere as depicted in
equidistant projection on plane of observer’s rational
horizon. P – is the elevated pole. X – is the position of heavenly body on the celestial
sphere Z – is the zenith of the observer QZ- is the latitude of the observer. Angle PZX- azimuth angle
