Astrophysics is the study of the physical makeup and behaviour of celestial objects. Astrophysics and astronomy are not sharply distinguished. The tern astronomy is used to define the whole science of celestial objects; the term astrophysics applies to that portion of astronomy dealing with the applications of physical laws.

Astrophysics is largely concerned with studying the composition of stars, including main sequence stars such as our sun, double or binary stars, and star clusters. Astrophysical research also includes studies of galaxies, quasars, and the expanding universe.

Astrophysics uses many branches of physics; nuclear physics, to study power generation in stars; atomic physics, to understand the spectra and gaseous nebulae; gas laws and magnetic theory, to probe starspots and flares on star surfaces.