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- https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Stellar_Atmospheres_(Tatum)/01%3A_Definitions_of_and_Relations_between_Quantities_used_in_Radiation_Theory/1.12%3A_Radiance_LSince 1979 we have gone one step further, recognizing that obtaining and measuring the radiation from a black body at the temperature of melting platinum is a matter of some practical difficulty, and ...Since 1979 we have gone one step further, recognizing that obtaining and measuring the radiation from a black body at the temperature of melting platinum is a matter of some practical difficulty, and the current definition of the candela makes no mention of platinum or of a black body, and the candela is defined in such a manner that if a source of monochromatic radiation of frequency 5.4×1014Hz has a radiant intensity of 1/683 W sr−1 in that direction, the…
- https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Planetary_Photometry_(Tatum_and_Fairbairn)/01%3A_Principles_of_Planetary_Photometry/1.02%3A_Radiance_and_the_Equation_of_Transferprojected on a plane at right angles to the line of sight from the observer); or it is the power arriving per unit area at the observer from unit solid angle (subtended at the observer) of the extende...projected on a plane at right angles to the line of sight from the observer); or it is the power arriving per unit area at the observer from unit solid angle (subtended at the observer) of the extended source. Here dLds is the rate of change of radiance with, and in the direction of, position s in a given medium, r is the density of the medium (kg m -3 ) and κ is the mass attenuation coefficient (m 2 kg -1 ).
- https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Stellar_Atmospheres_(Tatum)/09%3A_Oscillator_Strengths_and_Related_Topics/9.01%3A_Introduction%2C_Radiance%2C_and_Equivalent_WidthIt is an intrinsic property of the atom, or rather of the two atomic levels involved in the formation of the line, which determines how much energy a single atom emits or absorbs. There are three quan...It is an intrinsic property of the atom, or rather of the two atomic levels involved in the formation of the line, which determines how much energy a single atom emits or absorbs. There are three quantities commonly used to describe this property, namely oscillator strength, Einstein coefficient and line strength.
