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POLLUX

In northern spring evenings, the "twin" stars Castor and Pollux of the constellation Gemini descend the northwestern sky looking like a pair of eyes staring down at the Earth. They are twins only in mythology, these warriors, Pollux fathered by Zeus and divine, Castor mortal, both placed in the sky to allow them to be together for all time. The northernmost of the zodiacal constellations, Gemini is also among the brightest, helped by first magnitude Pollux and second magnitude Castor. An exception to the rule, brighter Pollux, the sky's 17th brightest star, was given the Beta designation by Bayer, while somewhat fainter Castor is known as Alpha Geminorum. In fact, Pollux and Castor are nothing like twins, Castor a white quadruple star with fairly hot components (actually sextuple if you count a distant pair of companions) and Pollux an orange-colored cool giant, the nice pairing with Castor making Pollux's color more vivid. From its distance of 34 light years, we calculate a visual luminosity for Pollux 32 times that of the Sun, and coupled with its 4500 degree-Kelvin temperature, a diameter some 11 times solar, making it smaller than most of its cool giant brethren and only a quarter the dimension of Aldebaran. Direct measures of angular size, however, yield a somewhat smaller diameter 8.3 times that of the Sun. As a warmer kind of giant star, Pollux emits X-rays and seems to have a hot, outer, magnetically supported corona perhaps similar to that surrounding our Sun.