MENKENT (Theta Centauri). Centaurus is dominated by its two brightest stars, Rigil Kentaurus (Alpha Centauri, third brightest star in the sky and the nearest star to the Earth) and first magnitude Hadar (Beta Centauri). Though these two shine brilliantly to the lucky residents of the southern hemisphere, neither is visible from mid-northern latitudes, so if those that live there wish to know Centaurus, they must begin with the third brightest star in the constellation, Menkent, to which is assigned the rather lowly letter Greek letter Theta (Gamma Centauri rather oddly coming in second). The name comes from an Arabic word for "shoulder" (of the Centaur), to which is attached the Latin abbreviation for "Kentaurus" for Centaur, tying Menkent back to the constellation's luminary, Rigil Kentaurus. Menkent, at mid-second magnitude (2.06) is but four percent fainter to the eye than Polaris. Much closer than Polaris, however, only 61 light years away, it is intrinsically much less luminous. At the warm end of class K (K0), the star is a near- clone of the northern hemisphere's Pollux, just fainter to the eye than Pollux because it is 80 percent more distant. Menkent, with no known or even suspected companions, is about as pure a sample of its class you can come by. From its 4780 Kelvin surface, this yellow-orange star radiates at a luminosity 60 times that of the Sun, the star's radius 11 times solar. Well along in its evolution, Menkent is now fusing helium into carbon and oxygen in its deep core. The star's only offbeat property is its rather high "proper motion," its speed across the line of sight. Approaching us at only one kilometer per second, it is speeding past us at 65 kilometers per second, about twice "normal," suggesting that the star really belongs to the outer part of the Galaxy's disk and is only visiting the solar neighborhood.
Written by Jim Kaler. Return to STARS.