When one star equals four

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.

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