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MUSCIDA

(Omicron Ursae Majoris). While not part of Ursa Major's "Dipper", Muscida holds a special place as the Great Bear's snout, the star that leads the beast around the north celestial pole. The name, one of the few that comes directly from Latin, appropriately means "muzzle." While many of the brighter stars of Ursa Major are relatively common white stars of class A or orange giants of class K, Muscida stands out as a "yellow" class G (G5) giant. An easily visible third magnitude (3.36), Muscida shines with the light of 140 Suns from a distance of 185 light years. That and the well-determined temperature of 5157 Kelvin (a bit cooler than the Sun) reveal a star with a radius 15 times solar, the spectrum showing a metal content closely solar. Spinning with a slow velocity of at least 3 kilometers per second, as befits a giant, the star may take as much as 250 days to make a complete rotation. This 3 solar mass giant, which began life 360 million years ago as a hot class B dwarf, is now passing through the "Hertzsprung Gap," a region of temperature that is transited quickly as the star -- which has a dead helium core -- prepares to become a much brighter red giant. The speed of evolution is fast enough that such stars are relatively rare. Close examination reveals that Muscida is also an unclassified variable, changing from magnitude 3.3 to 3.8 over a rough period of about a year. Other than its state of evolution, the star's most distinguishing characteristic is its tiny companion, a 15th magnitude class M1 red dwarf about which nothing else is known. At a distance of at least 400 Astronomical Units (10 times the distance between the Sun and Pluto), faint Muscida-B takes at least 4100 years to make a complete circuit around Muscida-A, so long that no orbital motion has yet actually been seen. From Muscida-A, the red dwarf would appear some 10 times brighter than Venus does in our sky, while from Muscida-B, the giant would glow with the light of 700 full Moons.