Einstein's theory of relativity and its theory of gravitation are the base of the present understanding of the universe.
General relativity is the foundation for modern cosmology - the study of the universe as a whole.
The basic method used to measure distances in the universe employs geometry and measures the paralax of a star. Paralax is the apparent motion of a star against the background of more distant stars due to the Earth's motion. Other examples of paralax include the way the moon appears to follow a moving autombile at night, or, when driving past two trees of different distances, one will appear to scale in front of the other. The distance is measured according to the included diagram, using trigonometric functions tan, sin, and cos. Nonetheless, Astrophysicists have pieced together theoretical stellar evolutions.