Due to the Sun's position, which currently lies 56.75 ☖.20 ly north of the midplane, and the heliocentric definition adopted by the IAU, the galactic coordinates of Sgr A* are latitude +0° 07′ 12″ south, longitude 0° 04′ 06″. Rounded to the same number of digits as the table, 17 h 45.7 m, −29.01° (J2000), there is an offset of about 0.07° from the defined coordinate center, well within the 1958 error estimate of ☐.1°. Radio source Sagittarius A*, which is the best physical marker of the true Galactic Center, is located at 17 h 45 m 40.0409 s, −29° 00′ 28.118″ (J2000). The IAU recommended that during the transition period from the old, pre-1958 system to the new, the old longitude and latitude should be designated l I and b I while the new should be designated l II and b II. J2000.0 equatorial coordinates approximating the galactic reference points Based on this definition, the galactic poles and equator can be found from spherical trigonometry and can be precessed to other epochs see the table. Galactic latitude is positive towards the north galactic pole, with a plane passing through the Sun and parallel to the galactic equator being 0°, whilst the poles are ☙0°. The galactic longitude increases in the same direction as right ascension. Longitude 0° is the great semicircle that originates from this point along the line in position angle 123° with respect to the equatorial pole. In the equatorial coordinate system, for equinox and equator of 1950.0, the north galactic pole is defined at right ascension 12 h 49 m, declination +27.4°, in the constellation Coma Berenices, with a probable error of ☐.1°. In 1958, the International Astronomical Union (IAU) defined the galactic coordinate system in reference to radio observations of galactic neutral hydrogen through the hydrogen line, changing the definition of the Galactic longitude by 32° and the latitude by 1.5°. A number of different coordinate systems, each differing by a few degrees, were used until 1932, when Lund Observatory assembled a set of conversion tables that defined a standard galactic coordinate system based on a galactic north pole at RA 12 h 40 m, dec +28° (in the B1900.0 epoch convention) and a 0° longitude at the point where the galactic plane and equatorial plane intersected. The first galactic coordinate system was used by William Herschel in 1785. See also: Galactic plane, Galactic Center, and Galactic anticenter
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