ABSTRACT
Eddington, Arthur Let us first understand what a galaxy is. The following is a recipe for making galaxies: Take about ten thousand million stars. Spread them so that on the average light takes three or four years to pass from one to the next. Add about the same amount of matter in the form of diffuse gas between the stars. Roll it all out flat. Set it spinning in its won plane. Then you will obtain an object which, viewed from a sufficient distance, will probably look more or less like a spiral nebula.
