Astroparticle Physics

402 C Definition of Equatorial and Galactic Coordinatesgalactic coordinateslongitudelatitudedistance from the SunIn contrast, galactic coordinates are fixed on our galaxy.The spherical coordinates (r,l,b) are centered on the Sun,with l being the galactic longitude and b the latitude. r is thedistance of the celestial object from the Sun. The galacticlongitude l is the angle between the direction to the galacticcenter and the projection of the direction to the star onto thegalactic plane. It counts from the direction to the galacticcenter (l = 0 degrees) via the galactic anticenter (180 degrees,away from the Sun) back to the galactic center. Thelatitude b varies from the +90 degrees (perpendicular abovethe galactic plane) to −90 degrees (Fig. C.2).starFig. C.2Definition of the galacticcoordinates latitude and longitudegalactic planerSunblgalactic center