# galactic coordinate system

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## galactic coordinate system,

astronomical coordinate systemastronomical coordinate systems.
A coordinate system is a method of indicating positions. Each coordinate is a quantity measured from some starting point along some line or curve, called a coordinate axis.
in which the principal axis is the galactic equator (the intersection of the plane of the Milky Way with the celestial spherecelestial sphere,
imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects. For these purposes, any astronomical object can be thought of as being located at the point where the line of sight
) and the reference points are the north galactic pole and the zero point on the galactic equator; the coordinates of a celestial body are its galactic longitude and galactic latitude. In the IAU galactic coordinate system, introduced in 1958 by the International Astronomical Union, the zero point on the galactic equator has the equatorial coordinates R.A. 17h39.3m and Dec. −28°55'; this lies in the direction of the center of our galaxy, the Milky Way.
galactic coordinate system

## galactic coordinate system

A coordinate system used to study the structure, surroundings, and contents of the Galaxy. The fundamental circle is the galactic equator and the zero point lies in the direction of the galactic center (in the constellation Sagittarius) as seen from Earth (see illustration). The coordinates are galactic latitude and longitude.

The galactic latitude (b) of a celestial body is its angular distance (from 0° to 90°) north (counted positive) or south (counted negative) of the galactic equator; it is measured along the great circle passing through the body and the galactic poles. The galactic longitude (l) of a celestial body is its angular distance (from 0° to 360°) from the nominal galactic center measured eastward along the galactic equator to the intersection of the great circle passing through the body.

The position of zero galactic longitude, i.e. the nominal galactic center, was agreed (1959) by the International Astronomical Union (IAU); it lies at RA 17h 45.6m, dec –28°56′.3 (2000.0). More recent observations suggest the actual galactic center coincides with a radio and infrared souce, Sagittarius A West, a few arc minutes from this nominal position; the nominal center is still used, however, as the zero point for galactic coordinates. The true center lies at l = –3′.34, b = –2′.75.

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