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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]
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 placed at a certain distance, 10 parsecs for stars. A more complex definition of absolute magnitude is used for planets and small Solar System bodies, based on its ...
"Absolute bolometric magnitude" (which term is redundant, practically speaking, since bolometric magnitudes are nearly always "absolute", i.e. corrected for distance) is a measure of the star's luminosity, summing over its emission at all wavelengths, and thus the total amount of energy radiated by a star every second.
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.
The absolute magnitude M, of a star or astronomical object is defined as the apparent magnitude it would have as seen from a distance of 10 parsecs (33 ly). The absolute magnitude of the Sun is 4.83 in the V band (visual), 4.68 in the Gaia satellite's G band (green) and 5.48 in the B band (blue). [20] [21] [22]
Deneb's absolute magnitude is estimated as −8.4, placing it among the visually brightest stars known, with an estimated luminosity of nearly 200,000 L ☉. This is towards the upper end of values published over the past few decades. [27] [28] By the distance from Hipparcos parallax, Deneb has a luminosity of 55,000 L ☉. [9]
Altair is an A-type main-sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle asterism; the other two vertices are marked by Deneb and Vega. [ 7 ] [ 15 ] [ 16 ] It is located at a distance of 16.7 light-years (5.1 parsecs ) from the Sun .
The name has two possible derivations, both listed in Richard Hinckley Allen's seminal Star Names: Their Lore and Meaning. The brightest star in the obsolete constellation of Argo Navis, which represented the ship used by Jason and the Argonauts, was given the name of a ship's pilot from another Greek legend: Canopus, pilot of Menelaus' ship on ...