Classically, physics was interested only in mechanics, electricity and magnetism, thermodynamics, and optics. With the many advances of the Twentieth Century, however, these studies have had to be modified to incorporate quantum mechanics and relativistic physics. In addition, atomic physics, nuclear physics, and elementary particle physics have developed into complex studies in recent decades. Astronomy, which may be considered a branch of experimental physics, is the observational and mechanical study of celestial objects, the space between them, and the universe as a whole. As a result, many of the advances in astronomy occur in step with advances in physics, and it is often difficult to separate the two.
Astrophysics combines the theories , observations, and experiments of astronomy and physics.
It is the study of the properties, constitution, structure, and evolution of celestial bodies and the intervening regions of space, including the production and expenditure of energy in these systems. Cosmology, special and general relativity, particle physics, and plasma physics are some of the larger disciplines related to astrophysics. The study of physics provides a foundation whose support can be seen in all the other sciences. In addition, it provides insights into everyday phenomena, develops analytical thinking skills, and demonstrates the nature of the universe. While a challenging discipline, it is certainly one of the most rewarding.