Adhara or Epsilon Canis Majoris (Eps CMa) is the 2nd brightest naked eye star in the constellation Canis Major. With an apparent magnitude of 1.5, Adhara is the 22nd brightest star in the entire sky (see: 50 Brightest Stars ). Its absolute magnitude is -4.1 and its distance is 431 light years. The Equinox J2000 equatorial coordinates are RA = 06h 58m 37.5s, Dec = -28° 58' 20".

Adhara has a spectral type of B2II, a surface temperature of 24,750° Kelvin and a luminosity 20,000 times the Sun. It has a mass of 10 solar masses and a diameter ? times the Sun.

The image above shows the uncropped view of Adhara (North is up) through the Takahashi E-180 Astrograph.

Adhara is a binary star, about 430 light years from Earth. The primary star is blueish-white (spectral type B2) with a high surface temperature (25,000° K). It emits a total radiation equal to 20,000 times that of the Sun. If this star were at the same distance as Sirius, it would outshine all other stars in the sky and would appear 15 times brighter than the planet Venus. This star is also one of the brightest known extreme ultraviolet sources in the sky. It is the strongest source of photons capable of ionizing hydrogen atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the Local Interstellar Cloud.

The +7.5 magnitude companion star is at 7.5 arc-seconds away. Nevertheless, the components can only be resolved in large telescopes, since the main star is approximately 250 times brighter than its companion.

A few million years ago, Adhara was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4,700,000 years ago, Adhara was 34 light years from the Sun, and was the brightest star in the sky with an apparant magnitude of -3.99. No other star has attained this brightness since, nor will any other star attain this brightness within the next five million years.

The description above is based on the Adhara entry in Wikipedia. For more information about Adhara, see Stars (Jim Kaler).

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