Galactic coordinate systemThe galactic coordinate system is a celestial coordinate system that uses the Milky Way as its fundamental plane. The latitudinal angle is called the galactic latitude, and the longitudinal angle is called the galactic longitude. This coordinate system is useful for studying the galaxy itself. For example, you might want to know how the density of stars changes as a function of galactic latitude, to how much the disk of the Milky Way is flattened.
This article originates from Jason Harris' Astroinfo which comes along with KStars, a Desktop Planetarium for Linu/KDE. See http://edu.kde.org/kstars/index.phtml