astrophysics

The physical theory of astronomical objects and phenomena. The term was introduced in the nineteenth century to draw a distinction between the application of physics to interpret observations and the recording of positions, movements and phenomena that characterized astronomy of an earlier era. Thus it encompasses topics such as the structure and stability of stars, the propagation of electromagnetic radiation in space and the production of spectra, nuclear processes in stars and applications of gravitational theory. Though the term astrophysics retains its original meaning, "astronomy" is now generally considered to encompass all aspects of the study of the universe, including astrophysics. The scientific method we use today means that all astronomical work must draw on a knowledge of physics.