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Rasalas

(Mu Leonis). Leo's great head, signified by a backward question mark, more commonly known as the "Sickle," is famed for announcing northern spring skies. At the bottom of the Sickle lies first magnitude Regulus, while at the top is Rasalas, to which Bayer gave the greek letter Mu. The name, originally "Rasalasad Borealis," taken from an Arabic phrase (to which was attached the Latin "Borealis" for "northern"), refers to the "northern part of Leo's head" (Epsilon, a bit to the southeast of Rasalas, being the "southern part"). At first, the star looks like one more class K (K3) giant. But it is one with a difference. Or maybe even a pair of differences. At the brighter end of fourth magnitude (3.88), Rasalas shines from a distance of 133 light years. Factoring in its coolish temperature of 4500 Kelvin, which allows for a correction of a bit of infrared radiation, the star is found to radiate 65 solar luminosities into space, which combined with temperature yields a radius of 13 times that of the Sun. Unlike most K giants, which are quietly fusing helium into carbon and oxygen in their deep cores, this one, with a mass of about 1.5 to 1.7 times that of the Sun, appears to be in an earlier stage, one in which the helium core is still contracting. As such, it is getting ever brighter. Only 50 million years from now, the star will have increased its brightness by a factor of 10 to 20, and -- would were it as the same distance as today (which it will not be) -- will glower redly at first magnitude. Rasalas is also one of the sky's prominent "super-metal-rich" giants. Though astronomers vigorously argue the exact numbers, all agree that the star has a significantly higher metal content than does the Sun, the best estimate leading to an iron content about 70 percent greater than solar. The star's birthplace must have been especially enriched. The stars that are being orbited by newly-discovered planets also tend quite strongly to be metal-rich. Perhaps Rasalas, which will soon expand to a radius half that of Earth's orbit (and eventually, when its helium-fusion dies out, become even bigger), is in the process of destroying its inner planets.