Astronomy and Physics. The intensity of light observed from a light source, esp. a star or other celestial object (cf. magnitude, n. 3a). Also…

the brightness of a star or other celestial object as it would be as seen from a standard distance (now usually ten parsecs); cf. absolute magnitude…

(a) energy emanating from the sun in the form of heat, light, etc.; (now chiefly) power generated by harnessing this energy, solar power; (b) the…

Astronomy. The intrinsic brightness of a heavenly body (as distinct from its apparent brightness, diminished by distance); the rate of emission of…