# Galactic Coordinate System and distance

If the Galactic Coordinate System is made up of two values, angles of longitude and latitude, how is distance measured? If you have those two values, you get a line from the sun in a certain direction. There might be multiple objects on that line, how can you specify one of them in the coordinate?

• I prefer the X,Y,Z galactic coordinate system: In that system the sun is at 0,0,0. Positive X is in the direction toward the galactic center (The sun is approximately 70 light years above the galactic plane, depending on what source you read since the plane is not well defined. (ie. Humphreys and Larsen ApJ May 31,1995) This is obviously insignificant compared to the distance to the galactic center. Y is parallel to the plane, perpendicular to the X axis and positive in the direction of galactic rotation (which is counterclockwise if you consider the sun "above" the plane and you are looking " Dec 19, 2019 at 1:27
• down" on the plane from the sun). The Z axis then is obviously perpendicular to X and Y and positive Z is in the "Galactic North" direction. (ie. using the approximate figure, the galactic plane would be at Z = -70 LY) Once you have galactic coordinates in this system (there are a couple of good websites that will give you these (year 2000 coordinates)), it's child's play to make a 3D map of local stars. Dec 19, 2019 at 1:27