Luminosity of a Star

the intensity of light from a star, that is, the magnitude of the luminous flux radiated by a star in a unit solid angle. The expression “luminosity of a star” does not correspond to the term “luminosity” in general photometry. The luminosity of a star may be referred to some region of the stellar spectrum, such as the visual or photographic stellar luminosity, or to the total radiation from the star—the bolometric luminosity of the star. The stellar luminosity is usually expressed in units equal to the luminosity of the sun, or 3 × 10²⁷ international candles (3.8 × 10³³ ergs/sec). The luminosities of individual stars differ greatly. Some stars—supergiants of spectral class O—have bolometric luminosities up to one-half million times greater than the sun luminosity. Others have a bolometric luminosity smaller than that of the sun by a factor of hundreds of thousands. It is believed there are stars with still lower luminosity. Along with the mass, radius, and surface temperature of a star, luminosity is an important stellar characteristic. The relations between these stellar characteristics are studied in theoretical astrophysics. The luminosity L of a star is related to the absolute stellar magnitude M by the equation M = – 2.5 log L + 4.77.