By Wikipedia's own definition of astrophysics, it says,
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions.
Our astronomy page gives a definition of astronomy which is much broader than that so I must say that, according to the definitions we have now, astrophysics is a branch of astronomy. Zrallo 20:45, 14 June 2007 (UTC)[reply]