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The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an approximation of the galactic plane but offset to its north.
In actual astronomical practice, the delineation of the galactic quadrants is based upon the galactic coordinate system, which places the Sun as the pole of the mapping system. The Sun is used instead of the Galactic Center for practical reasons since all astronomical observations (by humans) to date have been based on Earth or within the Solar ...
The galactic coordinate system uses the approximate plane of the Milky Way Galaxy as its fundamental plane. The Solar System is still the center of the coordinate system, and the zero point is defined as the direction towards the Galactic Center. Galactic latitude resembles the elevation above the galactic plane and galactic longitude ...
The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. [ 1 ] [ 2 ] Its central massive object is a supermassive black hole of about 4 million solar masses , which is called Sagittarius A* , [ 3 ] [ 4 ] [ 5 ] a compact radio source which is almost exactly at the galactic rotational ...
The Sun follows the solar circle (eccentricity e < 0.1) at a speed of about 255 km/s in a clockwise direction when viewed from the galactic north pole at a radius of ≈ 8.34 kpc [4] about the center of the galaxy near Sgr A*, and has only a slight motion, towards the solar apex, relative to the LSR. [5] [6]
The zero of longitude of galactic coordinates was also defined in 1959 to be at position angle 123° from the north celestial pole. Thus the zero longitude point on the galactic equator was at 17 h 42 m 26.603 s , −28° 55′ 00.445″ (B1950) or 17 h 45 m 37.224 s , −28° 56′ 10.23″ (J2000), and its J2000 position angle is 122.932°.
In the galactic coordinate system, the space velocity components of Vega are (U, V, W) = (−16.1 ± 0.3, −6.3 ± 0.8, −7.7 ± 0.3) km/s, for a net space velocity of 19 km/s. [84] The radial component of this velocity—in the direction of the Sun—is −13.9 km/s, while the transverse velocity is 12.9 km/s.
The Carrington heliographic coordinate system, established by Richard C. Carrington in 1863, rotates with the Sun at a fixed rate based on the observed rotation of low-latitude sunspots. It rotates with a sidereal period of exactly 25.38 days, which corresponds to a mean synodic period of 27.2753 days.