*astrophysics*

n. [ Astro- + physics. ] (Astron.) The science treating of the physical characteristics of the stars and other heavenly bodies, their chemical constitution, light, heat, atmospheres, etc. It is a branch of astronomy. [ 1913 Webster ]

☞ Its observations were traditionally made with the spectroscope, bolometer, etc., usually in connection with the telescope. In modern times, radiotelescopes, infrared telescopes, X-ray and gamma ray detectors and neutrino detection equipment located deep underground are all put into service to observe and test theories about astronomical phenomena. [ Webster 1913 Suppl. +PJC ]