(1) The difference between the greatest value of a quantity and its average value. Distinguished from range, which is the difference between the greatest value and the least value.

(2) The angle, at an observer, measured in a horizontal plane from east or west to a celestial body. The term is used in this sense only for bodies whose centres are on the celestial horizon, and is prefixed with E if the body is rising and W if it is setting. It is given the prefix N or S to agree with the body's declination.

(3) Angular distance north or south of the prime vertical.