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The solar luminosity (L ☉) is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal solar luminosity is defined by the International Astronomical Union to be 3.828 × 10 26 W. [2]
In astronomy, this amount is equal to one solar luminosity, represented by the symbol L ⊙. A star with four times the radiative power of the Sun has a luminosity of 4 L ⊙. 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.
The Sun is found on the main sequence at luminosity 1 (absolute magnitude 4.8) and B−V color index 0.66 (temperature 5780 K, spectral type G2V). The Hertzsprung–Russell diagram (abbreviated as H–R diagram , HR diagram or HRD ) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and ...
Under the present atmospheric composition, this past solar luminosity would have been insufficient to prevent water from uniformly freezing. There is nonetheless evidence that liquid water was already present in the Hadean [6] [7] and Archean [8] [6] eons, leading to what is known as the faint young Sun paradox. [9]
Solar irradiance varies systematically over the cycle, [69] both in total irradiance and in its relative components (UV vs visible and other frequencies). The solar luminosity is an estimated 0.07 percent brighter during the mid-cycle solar maximum than the terminal solar minimum.
However, on this SI power scale, the nominal solar luminosity corresponds closely to M bol = 4.74, a value that was commonly adopted by astronomers before the 2015 IAU resolution. [ 10 ] The luminosity of the star in watts can be calculated as a function of its absolute bolometric magnitude M bol as: L ⋆ = L 0 10 − 0.4 M b o l ...
A near-infrared image of the R136 cluster. This cluster contains many of the most luminous known stars, including R136a1.Credit: ESO/VLT. This is a list of stars arranged by their absolute magnitude – their intrinsic stellar luminosity.
An example is the Meeus smoothing formula, [7] with related solar cycles characteristics available in this STCE news item. [ 8 ] The start of solar cycle 25 was declared by SIDC on September 15, 2020 as being in December 2019. [ 9 ]