Adhara

Adhara (Epsilon Canis Majoris / ε CMa / 21 Canis Majoris) is a star in the constellation Canis Major of apparent magnitude +1.51. It has the Bayer designation «Epsilon", fifth letter of the Greek alphabet, despite being the second brightest in its constellation and one of the brightest in the night sky.

Name

The traditional name of Adhara—sometimes written Adara or Adharaz—comes from the Arabic word عذارى 'aðāra', "virgins." ». Its main meaning is "orange blossom", hence its derivation to "virgins" because it is the flower representative of purity.

It is known in China as 弧矢七, "the seventh star of the bow and arrow."

Physical characteristics

Adhara is a binary star distant 405 light years from the Sun. The main star is a blue supergiant or luminous giant of a spectral type B2Iab. It has a surface temperature of 21,900 K and has a luminosity (total radiation) equivalent to 22,300 times that of the Sun. If it were at the same distance as Sirius (α Canis Majoris) it would have an apparent magnitude of -7 and would be seen 7 times brighter than the planet Venus. This star is also one of the brightest known emitters of ultraviolet rays in the sky. The measurement of its angular diameter leads to a radius of 10.4 times the solar radius. Its luminosity and temperature parameters allow its mass to be estimated at between 11 and 12 times the mass of the Sun, which is probably enough for it to explode as a supernova in the future.

The secondary component of the Adhara system, of 8th or 9th magnitude, is probably a star on the boundary between types A and F. Visually 7 arcseconds from Adhara A, the actual separation from it is, at least, 900 astronomical units, its orbital period being greater than 7,500 years. Despite the relatively wide angular distance that separates them, the components can only be resolved by telescope, since the main star is about 250 times brighter than his partner.

About 4,700,000 years ago, Adhara was only 34 light-years from the solar system, making it the brightest star in the night sky with an apparent magnitude of -3.99. No other star has been as bright since then, nor will any star reach this brightness again for at least the next 5 million years.