This division has now been superceded as both astronomy and astrophysics broaden in scope. Specifically excluded from astrophysics are the study and measurement of the motions and positions of the stars and planets. Topics which lie mainly within the domain of astrophysics are general relativity , cosmology , the evolution and structure of stars , the composition of interstellar matter, and the study of certain very high energy particles produced by violent events.
General relativity is tested by astronomy and astrophysics.
The two stars are orbiting each other, and the rate at which their orbital speed reduces is exactly that predicted by general relativity. To investigate cosmology and the early universe, various techniques are employed. One of these involves careful measurement of what is known as the three degree background. We see it as a uniform energy background. Recent observations of slight irregularities in this background have given us important clues to how the galaxies evolved.