There are lots of stars in the visible universe that stagger the imagination based on sheer size or mass, such as Betelguese or the Pistol Star (discovered in 1990 using the Hubble Space Telescope).
Others stars are fascinating for their awesome flaming gas streams, such as Beta Lyrae or for their odd pairings and strange orbital dances, such as Capella.
Capella was first recorded by the vanished Mesopotamian Akkadian culture in the 20th century B.C.
Let's take a look at Capella, also known by its astronomical name Alpha Aurigae, which turns out to be a complex system of four suns-not one. For those curious in name origins, the name capella is derived from the Latin vulgate meaning "she-goat". This star system's identification with a she-goat goes back through the mists of time.
Capella, which appears as a bright yellow star, is visible in the night sky right now (see accompanying sky map). It is the brightest star in the constellation Auriga, the Charioteer, and the third-brightest star seen in the northern sky-Arcturus and Vega are brighter.
Up until about the year 158,000 B.C., Capella was no. 1 in brightness in the northern night sky but thanks to changes in its magnitude in prehistory, Capella was pushed from the top of the heap.
When you gaze at Capella you are looking across a gulf 42 light years. The light you see from Capella today left its surface in the year 1967, the same year three brave Apollo 1 astronauts-Gus Grissom, Ed White, and Roger Chaffee-died in a fire on a Cape Canaveral launch pad and the same year astronomers discovered the first pulsars and gamma ray bursts in space.
One reason to explain Capella's exceptional brightness is the fact that the star we see from Earth is not a single sun, but four neighboring stellar objects made up of two binary pairs. So, Capella is, correctly, a four star system.
Let's take a look at the complex Capella star system-
The first couple consists of very bright twin type-G giant stars (like Sun). But both G stars have a stellar radius nearly 10 times the Sun's making them giant Gs. This first stellar pair orbit near each other. The stars in pair 1 are believed to be on the verge of swelling into red giants. What appears to be happening with pair 1 is exactly what the future of our G-type star will be like.
Capella pair 2, orbiting 10,000 AUs (short for astronomical units; 1 AU equals 93 million miles) from the first pair, are red dwarfs.
The Capella system was the first group of astronomical objects to be imaged by an optical interferometer; its portrait was captured by the British Cambridge Optical Aperture Synthesis Telescope in 1995.
One fact about the Capellan system that astronomers find fascinating is that it is a source of deadly X-rays. While researchers aren't clear what's generating the X-rays, some experts have suggested that the corona of the system's most massive star is the source.
In addition to the pairs of stars already mentioned, Capella has six more visual companions-other suns that appear very close to Capella in the sky through an amateur telescope. However, these stars are not believed to be close enough to Capella to be included as part of the Capellan system.
For those of us who live in the north, beautiful Capella is a year-round jewel in the night sky-it never sets. It is always visible from the northern United States.
What's in the Sky: Look for the bright star system of Capella in the northeastern sky after midnight this week. The planets Venus and Mars join Capella in the northeast on July 4 at 3 a.m. (see sky map courtesy of J. Kirk Edwards).
Louis Varricchio, M.Sc., is a former NASA senior science writer. He is NASA-JPL Solar System Ambassador in Vermont and a second lieutenant in the U.S. Civil Air Patrol's Rutland Composite Squadron.