How do you find the radius of a galaxy, R, knowing the distance to that galaxy, and the distance between that galaxy and another right beside it. (Like a binary galaxy, we're assuming the distance to both the galaxies is the same). An equation is what I'm looking for, but the exact numbers are:

d to galaxies = 2.19*10^24 m
d between galaxies = 1.51*10^13 m
R of one galaxy = ?

Thanks!

Dear 2xamp

Have a look at this link to Astronomy Notes. Also read the following pages there! (http://www.astronomynotes.com/galaxy/s7.htm)

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I'm afraid the data you've provided isn't sufficient. Perhaps if you posted a picture of the problem that would help. This seems like a trig question, so I would have expected some other data such as the angular separation of the two galaxies in question. Also, be clear as to whether the "distance between galaxies = 1.51 x 10^13 m" is measured center-to-center or edge-to-edge.