|| Starpath online classroom || Celestial Navigation Glossary || Glossary Index || Home ||

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z 
Geographical Position

The point on earth directly below a celestial body; or put another way, a star can appear directly overhead only if you are standing at its GP. The latitude of the GP of a celestial body is called its declination; the longitude of the GP is called its Greenwich hour angle (GHA). As the earth rotates, the GPs of all celestial bodies move westward at about 15° of longitude each hour along the surface of the earth, locked in tracks of fixed latitudes equal to their declinations. (The moon is the only body whose declination track slips north or south a noticeable amount during a single day's pass around the earth). The main function of the Nautical Almanac is to tell us the precise location of the GPs of all celestial bodies, at all times, throughout the year.

Abbreviation:  GP

[close window]