ASTRONOMY Astronomy (from Greek : ἀστρονομία ) is a natural science that studies celestial objects and phenomena . It applies mathematics , physics , and chemistry in an effort to explain the origin of those objects and phenomena and their evolution . Objects of interest include planets , moons , stars , galaxies , and comets ; the phenomena also includes supernova explosions, gamma ray bursts , quasars com , blazars , pulsars , and cosmic microwave background radiation . More generally, all phenomena that originate outside Earth's atmosphere ki are within the purview of astronomy. A related but distinct subject is physical cosmology , which is the study of the Universe as a whole. [1]