(Redirected from Galactic plane)
The
anisotropy of the star density in the night sky makes the galactic coordinate system very useful for coordinating surveys, both those which require high densities of stars (at low galactic latitudes) and those which require a low density of stars (at high galactic latitudes)
The 'galactic coordinate system' is a spherical reference system on the sky where the origin is close to the apparent center of the
Milky Way, and the "equator" is aligned to the galactic plane. Similar to geographic coordinates, positions in the galactic coordinate system have latitudes and longitudes.
Definition
In
1959, the
IAU defined the galactic coordinate system in reference to the
Equatorial coordinate system.
[1] The north galactic pole is defined to be at
RA 12h49m,
Dec +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.
The equivalent system referred to
J2000 has
[2] the north galactic pole at 12h51m26.282s +27°07′42.01″ (J2000), the zero of longitude at the position angle of 122.932°. The point in the sky at which the galactic latitude and longitude are both zero is 17h45m37.224s −28°56′10.23″ (J2000). This is offset slightly from the
radio source Sagittarius A
★ , which is the best physical marker of the true
galactic center. Sagittarius A
★ is located at 17h45m40.04s −29°00′28.1″ (J2000), or galactic longitude 359°56′39.4″, galactic latitude -0°2′46.2″.
Nomenclature
The symbols ''l'' and ''b'' are used to represent the galactic longitude and latitude, respectively.
References
1. Blaauw, A., Gum, C. S., Pawsey, J. L., & Westerhout, G., Astrophysical Journal, v. 130, p. 702, available at http://adsabs.harvard.edu/
2. "The Proper Motion of Sagittarius A
★ ", Reid, M. J., and Brunthaler, A., The Astrophysical Journal, v616, pg. 883.
See also
★
Galaxy formation and evolution
★
disc (galaxy)
★
bulge (astronomy)
★
galactic halo
★
galactic corona
External references
★ http://fuse.pha.jhu.edu/support/tools/eqtogal.html (Equatorial/Galactic conversion tool)
★ http://heasarc.gsfc.nasa.gov/cgi-bin/Tools/convcoord/convcoord.pl (Universal coordinate converter)
★ http://star-www.st-and.ac.uk/~fv/webnotes/chapter8.htm
★
Where is M13? User Manual
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