Azimuth, in Astronomy, is an arch of the horizon intercepted between the meridian of a place, and the azimuth, or vertical circle, passing through the given object; or it is the angle formed at the zenith by the meridian and vertical circle. The azimuth of the sun, or a star, at the time of the equinox, is found by the following proportion. As the radius is to the tangent of the latitude of the place of observation, so is the tangent of the sun's, or star's, altitude, to the cosine of the azimuth from the south.

Magnetic Azimuth, is an arch of the horizon included between the magnetic meridian, and a vertical circle passing through the object It differs from the true azimuth, on account of the variation of the magnetic needle. The magnetic azimuth may be determined by observations with the azimuth compass, and the true azimuth calculated therefrom.