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Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. [1] [2] In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a star, galaxy, or other astronomical objects. [3] [4]
Nonthermal sources can have very high brightness temperatures. In pulsars the brightness temperature can reach 10 30 K. [9] For the radiation of a helium–neon laser with a power of 1 mW, a frequency spread Δf = 1 GHz, an output aperture of 1 mm 2, and a beam dispersion half-angle of 0.56 mrad, the brightness temperature would be 1.5 × 10 10 ...
The paradox is this: with the young Sun's output at only 70 percent of its current output, early Earth would be expected to be completely frozen, but early Earth seems to have had liquid water [2] and supported life. [3] The issue was raised by astronomers Carl Sagan and George Mullen in 1972. [4]
The object's actual luminosity is determined using the inverse-square law and the proportions of the object's apparent distance and luminosity distance. Another way to express the luminosity distance is through the flux-luminosity relationship, = where F is flux (W·m −2), and L is luminosity (W). From this the luminosity distance (in meters ...
The minimum brightness is about magnitude +1.6 [14] when Mars is on the opposite site of the Sun from the Earth. Rotational variations can elevate or suppress the brightness of Mars by 5% and global dust storms can increase its luminosity by 25%. [14] [18]
The apparent magnitude (m) is the brightness of an object and depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness. The absolute magnitude ( M ) describes the intrinsic luminosity emitted by an object and is defined to be equal to the apparent magnitude that the object would have if it were ...
Comets may have been potential sources of water for early Earth, researchers said this week.. When Earth formed around 4.6 billion years ago, some water likely existed in that gas and dust ...
Earth's albedo varies by a factor of 6, from 0.12 in the cloud-free case to 0.76 in the case of altostratus cloud. The absolute magnitude in the table corresponds to an albedo of 0.434. Due to the variability of the weather, Earth's apparent magnitude cannot be predicted as accurately as that of most other planets. [20]