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Consequently, a magnitude 1 star is about 2.5 times brighter than a magnitude 2 star, about 2.5 2 times brighter than a magnitude 3 star, about 2.5 3 times brighter than a magnitude 4 star, and so on. This is the modern magnitude system, which measures the brightness, not the apparent size, of stars.
For example, a magnitude 2.0 star is 2.512 times as bright as a magnitude 3.0 star, 6.31 times as magnitude 4.0, and 100 times magnitude 7.0. The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46.
M bol is the bolometric magnitude of the star; The new IAU absolute magnitude scale permanently disconnects the scale from the variable Sun. 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]
For example, Betelgeuse has the K-band apparent magnitude of −4.05. [5] Some stars, like Betelgeuse and Antares, are variable stars, changing their magnitude over days, months or years. In the table, the range of variation is indicated with the symbol "var". Single magnitude values quoted for variable stars come from a variety of sources.
The brightest stars, on either scale, have negative magnitude numbers. The variation in brightness (ΔL) between two stars is calculated by subtracting the magnitude number of the brighter star (m b) from the magnitude number of the fainter star (m f), then using the difference as an exponent for the base number 2.512; that is to say:
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.
First-magnitude stars are the brightest stars in the night sky, with apparent magnitudes lower (i.e. brighter) than +1.50. [ 1 ] [ 2 ] Hipparchus , in the 1st century BC , introduced the magnitude scale.
The apparent magnitude is the observed visible brightness from Earth which depends on the distance of the object. The absolute magnitude is the apparent magnitude at a distance of 10 pc (3.1 × 10 17 m), therefore the bolometric absolute magnitude is a logarithmic measure of the bolometric luminosity.