Capella << kuh PEHL uh >> also known as Alpha Aurigae, ranks as the seventh brightest star in the sky. As seen from Earth, only the sun and five other stars shine more brightly. Capella appears as the brightest star of the constellation Auriga, the Charioteer. To the ancient Greeks, the star represented Amalthea, the mythical goat that nursed the god Zeus in his infancy. The name Capella comes from the Latin word for little she-goat. Capella lies about 42 light-years from Earth. One light-year equals the distance light travels in a vacuum in a year, about 9.46 trillion kilometers.
Capella actually consists of four stars—two sets of binary (double) stars. The pairs lie roughly 0.2 light-year from each other.
One of the binary stars consists of a pair of large, bright stars called yellow giants. Each of these stars has roughly 2 1/2 times as much mass (amount of matter) as the sun. Their yellowish-orange glow indicates respective surface temperatures of about 5600 K and 5000 K, making them about as hot as the sun. One kelvin (K) equals one Celsius degree above absolute zero (–273.15 °C). The stars’ diameters measure about 6.9 and 12.7 times that of the sun. Because of their large sizes, the stars give off roughly 50 and 80 times as much light as does the sun. The stars lie about 1 astronomical unit from each other. An astronomical unit (AU) equals the average distance between Earth and the sun, about 150 million kilometers.
Capella’s other binary star consists of a pair of small, faint stars called red dwarfs. The stars have respective masses of about 10 and 40 percent that of the sun. They give off a total of about 1.5 percent as much light as does the sun.
See also Star (table: The 10 brightest stars as seen from Earth) .
