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RAS ALGETHI
Just to the west of the bright star Vega lies the constellation Hercules, which commemorates the great and strong mythological Greek hero. Though the brightest of its stars is only middling second magnitude, the constellation as a whole is fairly prominent. Rather oddly, Ras Algethi, the Alpha star, is the fifth brightest, perhaps because it is a bit south of the main constellation pattern. The name means "the Kneeler's Head, in reference to an early name for the constellation, the figure of the man seen upside down, his head toward the south. Though of the third magnitude as seen from Earth, the star itself is magnificent, a reddish giant or even supergiant with a surface temperature of about 3000 degrees Kelvin. At a distance of about 400 light years, Ras Algethi to the human eye is almost 500 times more luminous than the Sun, though in fact it varies irregularly in its brightness by about a magnitude over a period of years. Factoring in the infrared radiation that we cannot see from the cool star would make it almost 15 times brighter yet. True to its class, the star has a radius that is twice the distance between the Earth and Sun, which if placed here would take it well out past the orbit of Mars. Ras Algethi is a complex multiple star that through the telescope has a fifth magnitude companion five seconds of arc away. This secondary is itself a double that consists of a giant star about the temperature of the Sun and a more solar-like star somewhat hotter than the Sun in orbit around each other with a 52 day period. The bright supergiant is blowing a powerful wind that is so strong that the cloud of gas expanding around it has enveloped the companion, which is at least 550 astronomical units away from the supergiant, 275 times the supergiant's size and 14 times the dimension of our whole planetary system. Ras Algethi appears to be losing mass at a rate of about a ten-millionth of a solar mass per year, hardly a record, but substantial enough, consistent with its being a highly distended supergiant.