Luminosidade: diferenças entre revisões

[[ImagemFicheiro:MoonHaloDonnellyMillsWA 2005 SeanMcClean.jpg|thumb|right|200px|Noite de luar: a luz emitida pelo [[Sol]] é refletida pela [[Lua]] para a [[Terra]]]]

Or simplified, given m_sun = −26−26.73, dist_sun = 1.58 ×× 10^−5−5 lyr:

: m_star = −− 2.72 −− 2.5 ·· log(L_star/dist_star²)

::m_sun (@4.3lyr) = −2−2.72 −− 5 ·· log(1/4.3) = 0.45

:L_star/L_sun = (dist_star/dist_sun)² ·· 10^{{(m_sun −m−m_star) ·· 0.4}}

:L_star = 0.0813 ·· dist_star² ·· 10^{(−0−0.4 ·· m_star)} ·· L_sun

::Sirius is 8.6 lyr distant, and magnitude −1−1.47.

::Lum(Sirius) = 0.0813 ·· 8.6² ·· 10^{−0−0.4··(−1−1.47)} = 23.3 ×× Lum_sun

A bright [[star]] with [[absolute magnitude|bolometric magnitude]] −10−10 has a luminosity of 10⁶ ''L''_s, whereas a dim star with bolometric magnitude +17 has luminosity of 10^−5−5 ''L''_s. Note that [[absolute magnitude]] is directly related to luminosity, but [[apparent magnitude]] is also a function of distance. Since only apparent magnitude can be measured observationally, an estimate of distance is required to determine the luminosity of an object.