The Far 3 kpc Arm was discovered in 2008 by astronomer Tom Dame while preparing a talk on the galaxy's spiral arms for a meeting of the 212th American Astronomical Society. It is one of the spiral arms of the Milky Way and it is located in the first galactic quadrant at a distance of 3 kiloparsecs (9,800 light-years) from the Galactic Center. Along with the Near 3 kpc Arm, the existence of which has been known since the mid-1950s, the counterpart inner arms establish the symmetry of the Milky Way. Tom Dame and collaborator Patrick Thaddeus analyzed data obtained using a 1.2-meter-diameter millimeter-wave telescope located at Cerro Tololo Inter-American Observatory (CTIO) in Chile. They detected the presence of the spiral arm in a CO survey and later confirmed their discovery using 21-centimeter radio measurements of atomic hydrogen collected by colleagues in Australia.
See also Galactic disc
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