ALPHA HOR (Alpha Horologii). Horologium, the Clock, which trails down the southern sky parallel to long Eridanus, is so obscure that its luminary, Alpha Hor, is only fourth magnitude (though as a saving grace, at least a modestly bright fourth magnitude, 3.86), the rest fifth and fainter. Alpha Hor (no proper name) is in a way a special star, as it is so quiet and unassuming that it provides a fine standard against which others may be observationally compared. It is a common class K (K1) 4650 Kelvin orange giant, a "clump star" that is quietly fusing its core helium into carbon and oxygen. At a distance of 117 light years, and with a luminosity 47 times that of the Sun and a radius 11 times solar, the star's mass comes in at around double that of the Sun. About a billion years ago, just after its birth, it shone as a white class A star much like Sirius or Vega appear today. Not doing much at the moment, the star will eventually run out of core helium, and will begin to brighten as it prepares to eject its outer envelope and become a white dwarf. For now, it can just be admired as a peaceful star with no companion that is gradually moving away from us at a modest 22 kilometers per second. Without stars like this one as a benchmark, the other, more exciting ones, would be much more difficult to study.
Written by Jim Kaler. Return to STARS.