Long before a Hollywood ghost appropriated its name, Betelgeuse was one of the most famous stars in the sky. The name, pronounced "BET-el-jooze"(not "Beetlejuice" as in the 1988 movie), comes from the Arabic for "house of the twins." Apparently ancient observers considered the star, which lies in the constellation Orion, to be part of the neighboring constellation Gemini.
Betelgeuse is a red supergiant and in the last stage of its active lifetime (i.e., generating energy by nuclear fusion). A cool star, relatively speaking, Betelgeuse's light output varies. Still, it's bright enough for its reddish color to be detected by the naked eye.
The outer atmosphere of the star is so extended — to some 800 times the diameter of the sun — that its surface gravity is considerably weakened, allowing vast amounts of matter to flow into space in the form of stellar wind. Betelgeuse is awash in surrounding nebulosity (clouds of gases and dust) built up by these emissions. It is one of three bright stars that astronomers consider prime candidates to explode as supernovas. This could happen anytime in the next 100,000 years or so and is sure to be spectacular.
Planets of the Week
Saturn and Jupiter are found in the constellation Taurus, the Bull, and can be seen until an hour or two after midnight. Jupiter, large and bright, is one of the first "stars" visible when darkness falls. (The September 18 and September 25 Sky Guides provide more information on viewing our solar system's largest planets and the array of moons that surround them. Click here to read the former; click here to read the latter.)
Venus is setting more than three hours after sunset. Look in the southwestern sky after the sun goes down to spot the brilliant Evening Star, getting larger and brighter with each passing night this month. Sharp-eyed observers can even spot Venus in daylight. Mars is visible in the very early morning hours in the constellation Libra. Watch for it to brighten steadily throughout the first half of the year.
At 9:00 p.m. on February evenings, Cepheus the King, Cassiopeia the Queen, and Perseus the Hero are the most notable constellations in the northwestern portion of the sky. Cassiopeia is recognizable as a bright W shape that's visible from northern latitudes all year long. The constellation Auriga the Charioteer and its very bright alpha star, Capella, are very high in the northwest. Taurus the Bull, containing the conspicuous star cluster known as the Pleiades (or Seven Sisters) is in the west. Its other star cluster, the Hyades, which also represents a mythological group of sisters, marks the bull's face, while the bright orange star Aldebaran represents its eye.
Look toward the northeast and almost halfway up the sky to spot the Big Dipper, an asterism, or star shape, within the larger constellation Ursa Major (the Great Bear). The two stars at the end of the dipper's bowl are known as the Pointers, for a line drawn through them and extended northward points directly to Polaris, the North Star. Polaris marks the tip of the handle of the Little Dipper, which is in the constellation Ursa Minor, the Little Bear.
Gemini, the Twins, is in the southeastern part of the sky. It has two bright stars named Castor and Pollux, the twins born of an egg laid by Leda after she was seduced by Zeus in the guise of a swan. Procyon, the alpha (or brightest) star in Canis Minor, the Little Dog, is below Gemini. Most of the rest of this quadrant of the sky is occupied by faint constellations, the largest of which is Hydra, the Sea Serpent. Leo the Lion and its bright star Regulus are in the east.
Face southwest to see Orion. A very large and bright red giant star named Betelgeuse marks one shoulder, while a less bright red star called Bellatrix marks the other. The very hot bluish-white star Rigel marks one knee. The color contrast between the Orion's two brightest stars, Rigel and Betelgeuse, is evident even to the naked eye. Orion's three belt stars point toward Taurus in the west, Canis Major in the south, and Gemini and Auriga high overhead. The brightest star in the sky, Sirius, also known as the Dog Star, lies in Canis Major, the Great Dog.