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FOMALHAUT
This wonderful first magnitude star of northern- hemisphere autumn, usually pronounced "fo-ma-low," slides slowly in lonely grandeur above the southern horizon during the months of October and November. Well to the south of the Great Square of Pegasus, Fomalhaut marks for us the otherwise dim constellation Piscis Austrinus, the Southern Fish, not surprisingly also south of the more well-known zodiacal constellation Pisces, the Fishes. The Alpha star of the constellation, the name means the "fish's mouth," and comes from a longer Arabic phrase meaning "the mouth of the southern fish." It at first seems like yet another ordinary white "class A" star similar to, though a bit cooler than, Vega in Lyra (which passes nearly overhead in temperate latitudes) with a surface temperature of about 8500 Kelvin. It is quite close, only 25 light years away, from which we calculate a luminosity 16 times greater than the Sun. Almost the same distance as Vega, it is over a full magnitude fainter to the eye as a result of somewhat lower mass, which results in a lower surface temperature and smaller size. In 1983 an orbiting satellite called IRAS discovered far more infrared radiation coming from the star than expected. Infrared -- radiation which has waves longer than red light -- is a signature of a cool source. The radiation is coming from a huge disk of matter four times the dimension of our planetary system that surrounds the star much like those that encompass Vega and Denebola. The disk is thought to be made of icy dust particles that have been warmed by the star. The planets of our Solar System almost certainly formed from the accumulation of dust in just such a disk. Recent observations of Fomalhaut's disk shows a hole in the middle. Could the hole be the result of planets that have removed the dust? So far none have been detected. But keep your eye on the lonely one to the south.