Galactic coordinate system

The galactic coordinate system uses the sun as its origin. Galactic latitude is the angle between the galactic plane and the object. The galactic longitude is measured in the galactic plane in relation to the direction of the sun - galactic center . ${\displaystyle b}$ ${\displaystyle \ell }$

Longitudes of the galactic coordinate system

The galactic coordinate system is one of the astronomical coordinate systems used in spherical astronomy . It is useful for studying the Milky Way system .

The reference plane of the galactic coordinate system is the plane of the Milky Way , which is also called the galactic plane . For practical reasons, the zero point is not the galactic center , but the sun , since to this day all astronomical observations are based on the solar system .

• The galactic longitude is measured counterclockwise in the galactic plane (when looking from galactic north), see also galactic quadrant . ${\displaystyle l}$
• The galactic latitude is measured vertically, starting from the galactic center positive towards (galactic) north and negative towards south. ${\displaystyle b}$
• The third space coordinate of this spherical coordinate system is the distance of the point under consideration from the sun in the direction that is determined by longitude and latitude.

In 1958, today's galactic coordinates were introduced internationally and the equatorial coordinates (based on the Bessel epoch  B1950.0) were determined as follows:

• Galactic north pole (+ 90 ° galactic latitude): right ascension and declination (in the constellation Haar der Berenike ) ${\displaystyle \alpha =12\,\mathrm {h} \ 49\,\mathrm {min} }$ ${\displaystyle \delta =+27{,}40^{\circ }}$
• galactic center (0 ° galactic latitude, 0 ° galactic longitude): and (in the constellation Sagittarius ) ${\displaystyle \alpha =17\,\mathrm {h} \ 42{,}4\,\mathrm {min} }$ ${\displaystyle \delta =-28{,}92^{\circ }}$
• the galactic plane is inclined  to the celestial equator . ${\displaystyle 90^{\circ }-27{,}4^{\circ }=62{,}6^{\circ }}$

After establishing the galactic coordinate system, it turned out that the " prime meridian " of the galactic coordinates misses the actual galactic center at the location of the radio source Sagittarius A * by about 0.07 °. The galactic coordinates introduced in 1958 are still used.

Web links

• http://www2.arnes.si/~gljsentvid10/eqtogal_tool.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
• JavaScript converter between Galactic Coordinate System and Equatorial Coordinate System