<!-- linked from redirects North galactic pole and South galactic pole -->

thumb|upright=1.3|An artistic depiction of the Milky Way Galaxy showing the origin and orientation of galactic longitude. The galactic longitude () runs from the Sun upwards in the image through the center of the galaxy. The galactic latitude () is perpendicular to the image (i.e. coming out of the image) and also centered on the Sun.

The galactic coordinate system (GCS) 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. It uses the right-handed convention, meaning that coordinates are positive toward the north and toward the east in the fundamental plane.

Radio source Sagittarius A*, which is the best physical marker of the true Galactic Center, is located at , (J2000).

<math display="block">

\begin{align}

\sin(b) &= \sin(\delta_\text{NGP})\sin(\delta)+\cos(\delta_\text{NGP})\cos(\delta)\cos(\alpha-\alpha_\text{NGP}) \\

\cos(b) \sin(l_\text{NCP}-l) &= \cos(\delta)\sin(\alpha-\alpha_\text{NGP}) \\

\cos(b) \cos(l_\text{NCP}-l) &= \cos(\delta_\text{NGP}) \sin(\delta) - \sin(\delta_\text{NGP}) \cos(\delta) \cos(\alpha - \alpha_\text{NGP})

\end{align}

</math>

The reverse (galactic to equatorial) can also be accomplished with the following conversion formulas.

<math display="block">

\begin{align}

\sin (\delta) &= \sin (\delta_\text{NGP}) \sin(b) + \cos (\delta_\text{NGP}) \cos(b) \cos(l_\text{NCP} - l) \\

\cos (\delta) \sin(\alpha - \alpha_\text{NGP}) &= \cos(b) \sin(l_\text{NCP} - l) \\

\cos (\delta) \cos(\alpha - \alpha_\text{NGP}) &= \cos (\delta_\text{NGP}) \sin(b) - \sin(\delta_\text{NGP}) \cos(b) \cos(l_\text{NCP} - l)

\end{align}

</math>

Where:

<math display="block">\alpha_\text{NGP}=12^h 51.4^m \qquad \delta_\text{NGP}=27.13^{\circ} \qquad l_\text{NCP}=122.93314^{\circ}</math>

Rectangular coordinates

In some applications use is made of rectangular coordinates based on galactic longitude and latitude and distance. In some work regarding the distant past or future the galactic coordinate system is taken as rotating so that the -axis always goes to the centre of the galaxy.

There are two major rectangular variations of galactic coordinates, commonly used for computing space velocities of galactic objects. In these systems the -axes are designated , but the definitions vary by author. In one system, the axis is directed toward the Galactic Center ( = 0°), and it is a right-handed system (positive towards the east and towards the north galactic pole); in the other, the axis is directed toward the galactic anticenter ( = 180°), and it is a left-handed system (positive towards the east and towards the north galactic pole).

  • Universal coordinate converter .
  • Galactic Coordinate System - Wolfram Demonstration
  • Galactic coordinates, The Internet Encyclopedia of Science
  • Fiona Vincent, Positional Astronomy: Galactic coordinates , University of St Andrews
  • An Atlas of the Universe