The Sirius binary star system consists of a main sequence primary star of spectral class A1 called Sirius A and a white dwarf companion called Sirius B in orbit around their common center of mass with a period of about 50 years (see the later discussion of spectral classification of stars for definitions of these terms). The system is approximately 8.6 light years from Earth and lies in the constellation Canis Major (the Big Dog). The primary star, Sirius A, is the brightest star in our sky other than the Sun. The companion Sirius B was the first white dwarf discovered.