Selenographic Coordinates

numbers by means of which the positions of points on the surface of the moon are determined. Selenographic latitude and longitude are used as such coordinates.

The latitude of a point is the angular distance of the point from the lunar equator and is measured along the meridian passing through the point. North of the equator, the latitude is positive; south of the equator, it is negative. The north pole here is defined as the pole at which an observer sees the moon to be rotating in a counterclockwise direction.

The longitude of a point is the angle between the plane of the meridian of the point and the plane of the initial meridian. The initial meridian is defined as the meridian whose plane passes through the center of the earth when the libration in longitude (seeLIBRATION OF THE MOON) is equal to zero. Longitudes measured to the east of the initial meridian are regarded as positive; longitudes measured to the west of it are considered negative. It should be noted that this definition of positive and negative does not conform to the general rule established for planeto-graphic coordinates.