Establishing a Mutual Coordinate System for Interstellar Communication

[anorlunda]

I apologize for posting this question on a physics forum because it has a science fiction origin. However, I thought that real astronomers may have a real science answer to the question, so here goes.

Imagine two parties from distant parts of the galaxy in communication with each other. They want to exchange their locations in the galaxy. How do they agree on a mutual coordinate system?

In spherical coordinates, the radius from the galactic center is easy. But lattitude and longitude both need a zero degree reference. How to establish that reference?

My thought is that the obvious candidate is a line connecting the center of the Milky Way Galaxy with the center of the Andromeda Galaxy.

 

[mfb]

My thought is that the obvious candidate is a line connecting the center of the Milky Way Galaxy with the center of the Andromeda Galaxy.

Sure, and you can use the orientation of the disk as a second direction. The third direction can be chosen orthogonal to the two, and then you can set up every coordinate system you like.

Alternatively, use some very distant sources as reference, they will look nearly the same in the whole galaxy.
Or use very bright stars that can be seen by both, describe them via their absolute luminosity,spectral lines and other properties, and then set up a coordinate system based on them. That requires accurate distance measurements, of course.

 

[TurtleMeister]

You may be interested in reading about a real astronomical coordinate system, if you haven't already. The International Celestial Reference System (ICRS) has the solar system barycenter as it's origin and uses very distant radio sources, such as quasars, for it's reference.

 

[Chronos]

Pulsars would be useful for this purpose. Just give their position relative to Earth and frequency. Three such pulsars would triangulate your position and you need not know their exact distances.

 

[anorlunda]

Thanks to all. Every answer taught me something.

I like Chronos' answer best. It is just a variation on ordinary celestial navigation. The measurements needed to do it could (in principle if not in practicce) be done with an ancient mariner's sextant.

By the way, I realized that my own idea about Andromeda won't work because Andromeda may not be visible from all places in the Milky Way.