Editing Galactic coordinate system (section)

==Rectangular coordinates==
In some applications use is made of rectangular coordinates based on galactic longitude and latitude and distance. In some work regarding the distant past or future the galactic coordinate system is taken as rotating so that the {{math|''x''}}-axis always goes to the centre of the galaxy.<ref>For example {{cite journal |last=Bobylev |first=Vadim V. | date=March 2010 |title=Searching for Stars Closely Encountering with the Solar System |journal=Astronomy Letters |volume=36 |issue=3 |pages=220–226 |doi=10.1134/S1063773710030060 |arxiv=1003.2160 |bibcode=2010AstL...36..220B|s2cid=118374161 }}</ref>

There are two major [[Cartesian coordinate system|rectangular]] variations of galactic coordinates, commonly used for computing space velocities of galactic objects. In these systems the {{math|''xyz''}}-axes are designated {{math|''UVW''}}, but the definitions vary by author. In one system, the {{math|''U''}} axis is directed toward the Galactic Center ({{math|''l''}} = 0°), and it is a [[Right-hand rule|right-handed]] system (positive towards the east and towards the north galactic pole); in the other, the {{math|''U''}} axis is directed toward the galactic anticenter ({{math|''l''}} = 180°), and it is a left-handed system (positive towards the east and towards the north galactic pole).<ref name="Johnson" />

[[Image:Milky Way infrared.jpg|thumb|250px|The [[anisotropy]] of the star density in the night sky makes the galactic coordinate system very useful for coordinating surveys, both those that require high densities of stars at low galactic latitudes, and those that require a low density of stars at high galactic latitudes. For this image the [[Mollweide projection]] has been applied, typical in maps using galactic coordinates.]]