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When luminosity classes were added to the MK spectral classification scheme, Canopus was assigned class Iab indicating an intermediate luminosity supergiant. This was based on the relative strengths of certain spectral lines understood to be sensitive to the luminosity of a star. [ 47 ]
Occasionally, letters a and b are applied to luminosity classes other than supergiants; for example, a giant star slightly less luminous than typical may be given a luminosity class of IIIb, while a luminosity class IIIa indicates a star slightly brighter than a typical giant. [32]
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.
Canopus (α Carinae) 73.3 [96] AD Second brightest star in the night sky. Gacrux (γ Crucis) 73 [97] L/T eff: Twenty-sixth brightest star in the night sky. Polaris (α Ursae Minoris) 46.27 ± 0.42 [98] AD The current star in the North Pole. It is a Classical Cepheid variable, and the brightest example of its class. Aldebaran (α Tauri) 45.1 ± ...
This is a list of stars arranged by their apparent magnitude – their brightness as observed from Earth. It includes all stars brighter than magnitude +2.50 in visible light, measured using a V-band filter in the UBV photometric system.
A9II is also somewhat unusual, with F0 and a supergiant luminosity class being most common before 1989, but A9II is the most recent determination of an MK spectral class. The change is mainly due to a redetermination of the MK standards for "early F" stars (Gray & Garrison, 1989), as confirmed by Lopez-Cruz (1993).
astro: peak luminosity of the Sun in its thermally-pulsing, late AGB phase (≈5200x present) [69] 4.1 × 10 30 W astro: approximate luminosity of Canopus [70] 10 31: 2.53 × 10 31 W astro: approximate luminosity of the Beta Centauri triple star system [71] 3.3 × 10 31 W astro: approximate luminosity of Betelgeuse, a highly-evolved red ...
Canopus has persistently been the brightest star over the ages; other stars appear brighter only during relatively temporary periods, during which they are passing the Solar System at a much closer distance than Canopus.