Beginning of Essay
A star is a large ball of hot gas, thousands to millions of kilometers in diameter, emitting large amounts of radiant energy from nuclear reactions in its interior. differ fundamentally from planets in that they are self-luminous, whereas planets shine by reflect ....

Middle of Essay
.... by the Greek lower-case letter gamma) Ursa Minoris, and Betelgeuse, in Orion, is gamma Orionis. VARIABLE STARS (those which periodically change in brightness) have lettered names, such as RR Lyrae in the constellation Lyra. Fainter stars are known by their numbers in a catalog; HD 12938 is the 12,938th star in the Henry Draper Catalogue. CHARACTERISTICS OF STARS Each star in the universe has its own position, motion, size, mass, chemical composition, and temperature. Some stars are grouped into clusters, and stars and star clusters are collected in the larger groupings called galaxies. Our GALAXY, the Milky Way, contains more than 100 billion s ....