Sirius (Greek Seirios,"scorching"), also Dog Star, brightest star in the sky, situated in the constellation Canis Major. The star was highly venerated by the ancient Egyptians, who regarded it as a token of the rising of the Nile and of a subsequent good harvest. Many Egyptian temples were constructed in such a way that the light of Sirius reached the inner chambers. The hottest part of the summer coincides with the heliacal rising of Sirius, and thus acquired the name dog days.

The brilliance of Sirius is in large part a consequence of its relative nearness to the earth. The distance of the star from the earth is 8.7 light-years, or 51 trillion mi, and it is therefore one of the closest stars. It can be seen from every part of the earth. The mass of the star is 2.4 times that of the sun, and its surface temperature is higher than that of the sun. Irregularities in the motion of Sirius led the German astronomer Friedrich Bessel to believe that the star was accompanied by a hitherto unseen companion star. The companion was detected for the first time 18 years later in 1862 by the American astronomer Alvan Clark; it was later shown to be a white dwarf star.

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