CHARA (Beta Canum Venaticorum). A lovely name for a northern star that vaults the heavens in northern spring, "Chara" from Greek meaning "joy." Not terribly bright, just fourth magnitude (4.26), Chara (Beta Canum Venaticorum) is the fainter of the pair of stars that dominate the modern constellation of Canes Venatici, the Hunting Dogs, invented by Hevelius in the mid-1600s. The dogs are held by Bootes as he pursues Ursa Major around the pole, Chara and Cor Caroli (the Alpha star) helping make the "southern dog," the "northern dog" represented by a small group of stars to the northeast of Cor Caroli. Chara was originally the name for the southern dog itself, the northern called "Asterion" for "Little Star." But with the brighter of those that make the southern dog called "Cor Caroli," little Chara got the name to itself. Chara's most interesting aspect is its similarity to the Sun. The majority of bright naked eye stars are considerably more luminous than our own star, some vastly so, a natural result of their intrinsic brilliance, such stars visible over great distances. However, our Sun, a modest star in the middle of the full range of stellar brightness, would be invisible to the eye if only 70 light years away. At a distance of 27.3 light years (give or take just 0.1; second Hipparcos reduction), Chara provides a modestly good chance to see what the Sun would look like at stellar distances. It's a warm class G (G0) hydrogen-fusing dwarf with a temperature of 5880 Kelvin (only 100 degrees hotter than the Sun), a luminosity just 18 percent greater than solar, and a radius four percent larger. Direct measure of angular diameter gives very satisfying agreement of a radius three percent larger. Theory tells that the mass is very close to that of the Sun, the larger luminosity coming from a more advanced age (hydrogen-fusing stars slowly brightening and swelling as they age), Chara more like 7 billion years old, as opposed to the Sun's 4.6 billion. (The range is large, though, as other age estimates range from 4.1 billion years through 8.6 billion, even unto 12 billion.) Even though stars rotate more slowly with age, Chara (with a rotation speed of at least 3 kilometers per second) is spinning at least 50 percent faster than the Sun, giving a rotation period under 17 days. (Here we encounter even more uncertainty, as another estimate of rotation speed gives 11.5 km/s and a rotation period under 4 days, which is more in line with stellar youth.) Consistently, it's also detected in the X-ray part of the spectrum, implying that it too has a surrounding hot corona (rotation helping induce the necessary magnetic field). The biggest difference, other than luminosity, seems to be a metal content less than solar, the star having only about 60 percent as much iron. So (assuming the older age values) if you want to see the Sun from afar, plus what it will look like in a couple billion years, take a look at Canes Venatici's "southern dog." While there is no evidence for an orbiting planet, Chara may have a spectroscopically detected companion that orbits every 6.65 years at a probable distance of around 3 Astronomical Units. The reality of it, however, has been severely challenged, and it may not exist. If there IS a planet, its residents (given any) would see the Sun looking almost the same from there as Chara does to us.
Written by Jim Kaler 4/16/98; revised 10/13/09. Return to STARS.