Latitude ( or ). It is measured in degrees, minutes and seconds or decimal degrees, north or south of the equator. The precise measurement of latitude requires an understanding of the gravitational field of the Earth, either to set up theodolites or to determine GPS satellite orbits. The study of the figure of the Earth together with its gravitational field is the science of geodesy. This article relates to coordinate systems for the Earth: it may be extended to cover the Moon, planets and other celestial objects by a simple change of nomenclature. The graticule is formed by the lines of
Latitude ellipsoid and the distance . This height differs from the height above the geoid or a reference height such as that above mean sea level at a specified location. The direction of will also differ from the direction of a vertical plumb line. The relation of these different heights requires knowledge of the shape of the geoid and also the gravity field of the Earth. The geocentric latitude is the complement of the polar angle in conventional spherical polar coordinates in which the coordinates of a point are where is the distance of from the centre , is the angle