Astrophysics is the branch of
astronomy that employs the principles of physics and chemistry "to ascertain the nature of the
heavenly bodies, rather than their positions or motions in space." Among the objects studied are the
Sun, other
stars,
galaxies,
extrasolar planets, the
interstellar medium and the
cosmic microwave background. Their emissions are examined across all parts of the
electromagnetic spectrum, and the properties examined include
luminosity,
density,
temperature, and
chemical composition. Because astrophysics is a very broad subject,
astrophysicists typically apply many disciplines of physics, including
mechanics,
electromagnetism,
statistical mechanics,
thermodynamics,
quantum mechanics,
relativity,
nuclear and
particle physics, and
atomic and molecular physics.
