| Term: | GalacticCoordinateSystem |
| Definition: |
The International Astronomical Union (IAU) defined the galactic coordinate system in reference to the Equatorial coordinate system in 1958 The north galactic pole is defined to be at right ascension 12h 49m, declination +27.4� (B1950), and the zero of longitude is the great semicircle that originates from this point along the line in position angle 123� with respect to the equatorial pole. The galactic longitude increases in the same direction as right ascension. Galactic latitude is positive towards the north galactic pole, the poles themselves at �90� and the galactic equator being zero. |