luminosity

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luminosity in astronomy, the rate at which energy of all types is radiated by an object in all directions. A star's luminosity depends on its size and its temperature, varying as the square of the radius and the fourth power of the absolute surface temperature. The sun is a medium-sized star with a luminosity of 3.8×10 ³³ ergs per sec. The luminosities of other stars are commonly expressed in terms of the sun's luminosity. The known luminosities of stable stars range from about 1/1,000,000 that of the sun for a relatively cool white dwarf to about 1,000,000 times that of the sun for the hottest known supergiant star. See magnitude ; mass-luminosity relation ; stellar evolution .

luminosity (symbol L) The amount of radiation a star emits, corrected for interstellar absorption. It is expressed in watts, or in terms of the luminosity of the Sun (symbol L⨀), approximately 3.9 × 10²⁶ watts. Luminosity is related to the absolute bolometric magnitude (see absolute magnitude) of the star, M_bol, by the equationM_bol −4.72 = −2.5 log (L/L⨀)The luminosities of stars range from over 10⁵L⨀ for the brightest supergiants to less than 10⁻⁵ \ L⨀ for feeble red dwarfs. For X-ray sources it is usual to define luminosity not bolometrically but in particular passbands.

luminosity Absolute brightness of a star, given by the amount of energy radiated from its entire surface per second. It is expressed in watts (joules per second), or in terms of the Sun's luminosity. Bolometric luminosity is a measure of the star's total energy output, at all wavelengths. Absolute magnitude is an indication of luminosity at visual wavelengths.

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