BETELGEUSE

also called Alpha Orionis, brightest star in the constellation Orion, marking the eastern shoulder of the hunter. Its name is derived from the Arabic word bat al-dshauz, which means the giant's shoulder. Betelgeuse has an apparent magnitude of 0.4 and is one of the most luminous stars in the night sky. Though modern astronomers have detected little or no variability in its brightness, the English astronomer John Herschel claimed to have detected a small, irregular variability in 1836. Betelgeuse is easily discernible to even the casual observer, not only because of its brightness and position in the brilliant Orion but also because of its deep-reddish colour. The star is approximately 310 light-years from the Earth. Betelgeuse is one of the largest stars known. It is classified as a red supergiant; its diameter varies between 430 and 625 times the diameter of the Sun over a period of 5.8 years. For comparison, Mars's orbit around the Sun has a diameter that is 328 times that of the Sun.