Fig7_8Alpha_Centauri_and_southerncross_cc.jpg

Fig7_8Alpha_Centauri_and_southerncross_cc.jpg

Fig. 7.8 . Two of the most brilliant stars in the southern sky appear as a single star, named Alpha Centauri, to the unaided eye, but they can be resolved into two stars with the aid of binoculars or a small 5 cm (2-inch) telescope. The yellowish Alpha Centauri A (lower left), also known as Rigil Kentaurus, and the blue Alpha Centauri B (upper right) are locked together in a gravitational embrace, orbiting each other every 80 years. The two components of this binary star system can approach each other within 11.2 AU and may recede as far as 35.6 AU, where the mean distance between the Earth and the Sun is 1 AU. Both stars have a mass and luminosity that are comparable to those of the Sun. They appear bright because they are very nearby, at a distance of just 4.37 light-years. A third and faint companion Proxima Centauri (also see Fig. 7.5) is located at about 15,000 AU or 2.2 degrees from the two bright stars. At a distance of 4.24 light-years from the Earth, Proxima Centauri is the closest star other than the Sun. (Courtesy of ESO/Yuri Beletsky.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University