Sirius: Brightest Star in the Sky (Fact of the Day)

The big Sirius A and the tiny Sirius B
Sirius (The Dog Star) is the brightest star for us in the Earth. It does not mean that it is the most luminous as it appears very bright to us because it is very close to us and luminous than the other close stars. It is actually a binary star system consisting of two stars: Sirius A (Main-sequence star) and Sirius B (White Dwarf). It is about 8.6 light years from Earth, in the constellation of Canis Major.

Sirius A is about twice as massive and about 25 times luminous than our Sun. The binary system is about 200-300 million years old. But, when the system first formed, Sirius B was the more massive among the two but it became a white dwarf (and thus smaller) about 120 million years ago. Sirius B has about the same mass of our Sun (0.98 Solar mass) and approximately the size of our Earth.



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