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Blue and white supergiants are high luminosity stars somewhat cooler than the most luminous main sequence stars. A star like Deneb, for example, has a luminosity around 200,000 L ⊙, a spectral type of A2, and an effective temperature around 8,500 K, meaning it has a radius around 203 R ☉ (1.41 × 10 11 m).
L ★ is the star's luminosity (bolometric luminosity) in watts; L 0 is the zero point luminosity 3.0128 × 10 28 W; M bol is the bolometric magnitude of the star; The new IAU absolute magnitude scale permanently disconnects the scale from the variable Sun.
The first list shows a few of the known stars with an estimated luminosity of 1 million L ☉ or greater, including the stars in open cluster, OB association and H II region. The majority of stars thought to be more than 1 million L ☉ are shown, but the list is incomplete. The second list gives some notable stars for the purpose of comparison.
Note that the brighter the star, the smaller the magnitude: Bright "first magnitude" stars are "1st-class" stars, while stars barely visible to the naked eye are "sixth magnitude" or "6th-class". The system was a simple delineation of stellar brightness into six distinct groups but made no allowance for the variations in brightness within a group.
The derivation showed that stars can be approximately modelled as ideal gases, which was a new, somewhat radical idea at the time. What follows is a somewhat more modern approach based on the same principles. An important factor controlling the luminosity of a star (energy emitted per unit time) is the rate of energy dissipation through its bulk.
The luminosity class ranged from I to V, in order of decreasing luminosity. Stars of luminosity class V belonged to the main sequence. [7] In April 2018, astronomers reported the detection of the most distant "ordinary" (i.e., main sequence) star, named Icarus (formally, MACS J1149 Lensed Star 1), at 9 billion light-years away from Earth. [8] [9]
This implies that a star of magnitude m is about 2.512 times as bright as a star of magnitude m + 1. This figure, the fifth root of 100 , became known as Pogson's Ratio. [ 9 ] The 1884 Harvard Photometry and 1886 Potsdamer Duchmusterung star catalogs popularized Pogson's ratio, and eventually it became a de facto standard in modern astronomy to ...
The Yerkes spectral classification system is a two-dimensional scheme that uses a letter and number combination to denote the temperature of a star (e.g. A5 or M1) and a Roman numeral to indicate the luminosity relative to other stars of the same temperature. Luminosity class IV stars are the subgiants, located between main-sequence stars ...