STAR

any massive, self-luminous celestial body of gas that shines by radiant energy generated within its interior. The universe contains trillions of stars, only a very small percentage of which are visible to the unaided eye. The closest star to the solar system is Proxima Centauri, which is approximately 4.3 light-years from the Sun. The most distant stars lie in galaxies billions of light-years away. Stars may occur singly, as in the case of the Sun. More commonly, however, they exist in pairs, multiple systems with several members, or clusters consisting of numerous components. Furthermore, stars vary greatly in brightness, colour, temperature, mass, size, chemical composition, and age. any massive, self-luminous celestial body of gas that shines by radiation derived from its internal energy sources. Of the trillions of stars comprising the universe, only a very small percentage are visible to the naked eye. Many stars occur in pairs, multiple systems, and clusters. The members of such stellar groups are physically related through common origin and are bound by mutual gravitational attraction. Somewhat related to star clusters are stellar associations, which consist of loose groups of physically similar stars that have insufficient mass as a group to remain together as an organization. This article describes the properties and evolution of individual stars. Included in the discussion are the sizes, energetics, temperatures, masses, and chemical compositions of stars, as well as their distances and motions. The myriad other stars are compared to the Sun, strongly implying that our star is in no way special. Additional reading George O. Abell, Exploration of the Universe, 5th ed. (1987), a good introductory account of the properties of stars; Lawrence H. Aller, Atoms, Stars, and Nebulae, rev. ed. (1971), a semipopular work emphasizing analyses of starlight, stellar spectroscopy, and evolution, Astrophysics: The Atmospheres of the Sun and Stars, 2nd ed. (1963), and Astrophysics: Nuclear Transformations, Stellar Interiors, and Nebulae (1954), textbooks intended for senior students, treating ordinary stellar atmospheres, the Sun, variable stars including novas, and stars with extended envelopes; Martin Schwarzschild, Structure and Evolution of the Stars (1958, reissued 1965), one of the classic books on the subject, written before the widespread application of modern computers (moderately advanced level); Iosif S. Shklovskii, Stars: Their Birth, Life, and Death (1978; originally published in Russian, 1975), an examination of the achievements of 20th-century astrophysics in the area of star formation and evolution; Rudolf Kippenhahn, 100 Billion Suns: The Birth, Life, and Death of the Stars (1983; originally published in German, 1980), a readable account of stellar evolution; Donald A. Cooke, The Life & Death of Stars (1985), with excellent illustrations; Paul Murdin and Lesley Murdin, Supernovae, rev. ed. (1978), an excellent nontechnical history; and Albrecht Unsld and Bodo Baschek, The New Cosmos, 3rd rev. and enl. ed. (1983; originally published in German, 3rd rev. ed., 1983), a solid, somewhat technical introduction. Kenneth R. Lang and Owen Gingerich (eds.), A Source Book in Astronomy and Astrophysics, 19001975 (1979), provides a collection of seminal papers in the field, including much on stellar atmospheres, spectra, evolution and distribution, and variable stars. International reports of research in astronomical and astrophysical sciences, some technical, can be found in the following periodicals: Astronomical Journal (monthly) and Astrophysical Journal (semimonthly), both published by the American Astronomical Society; Astronomy and Astrophysics: A European Journal (semimonthly); Astrophysics (quarterly), trans. from Russian; and Chinese Astronomy and Astrophysics (quarterly), trans. from Chinese. For less technical articles, see Astronomy (monthly); American Association of Variable Star Observers, Journal (semiannual); Royal Astronomical Society, Quarterly Journal; and Sky and Telescope (monthly). Lawrence Hugh Aller Eric J. Chaisson