astronomy, uranology - the branch of physics that studies celestial bodies and the universe as a whole

coma - (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed

estraterrestrial body, extraterrestrial object - a natural object existing outside the earth and outside the earth's atmosphere

nucleus - (astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail