Astrophysics is the use of theories and ideas of physics in the study of space. Cosmology is the study of the universe as a whole. In space, distance is measured in light years. A light year is the equivalent of how far light travels in one year.
Stellar evolution involves the evolution of a star.
The star begins as a hydrogen cloud called a protostar. The protostar's hydrogen molecules fuse together to form helium. As the fusion of the hydrogen molecules fuse, there is a release of gamma rays, heat, and neutrinos. Then the red giant is formed. Soon, relative to stellar life, the hydrogen stops burning and the red giant collapses.