Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
September 2, 1996
Sirius: The Brightest Star in the Night
Credit: ROSAT, MPE, NASA, Courtesy Skyview
Copyright: University of Leicester
Explanation: Sirius is the brightest star in the night sky. Intrinsically, Sirius is over 20 times brighter than our Sun and over twice as massive. As Sirius is 8.7 light years distant, it is not the closest star system -- the Alpha Centauri system holds this distinction. Sirius is called the Dog Star because of its prominence in the constellation of Canis Majoris (Big Dog). In 1862, Sirius was discovered to be a binary star system with a companion star, Sirius B, 10,000 times dimmer than the bright primary, Sirius A. Sirius B was the first white dwarf star discovered, a type of star first understood by Subrahmanyan Chandrasekhar in 1930. While studying Sirius in 1718, Edmond Halley discovered that stars move with respect to each other. The Sirius system is shown above captured in X-ray light.
Authors & editors:
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.