Astronomy Fun Fact #86
The second popular coordinate system used by astronomers is the Galactic Coordinate System. This system is centered on the Sun, but it gives an object's position relative to the center of mass (CoM) of the Milky Way galaxy. That's pretty much where the supermassive black hole named Sagittarius A* sits.
The Milky Way is a barred spiral galaxy, so it has a central boxy region surrounded by a very large flat-ish disk of stars, dust, and gas. In the galactic coordinate system, an object's position is measured in three quantities.
1. Its distance from either the Sun or the center of the galaxy
2. Its angle above or below the disk of the galaxy. This is its galactic latitude, denoted by the letter b
3. Its angle within the disk of the galaxy. This is its galactic longitude, denoted by the letter l. The line that runs between the Sun and the center of the galaxy marks the l=0 line.