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ALPHA HOR (Alpha Horologii).Horologium,the Clock, which trails down the southern sky parallel to longEridanus, is so obscure that its luminary,Alpha Hor, is only fourth magnitude (though as a saving grace, atleast a modestly bright fourth magnitude, 3.86), the rest fifth andfainter. Alpha Hor (no proper name) is in a way a special star, asit is so quiet and unassuming that it provides a fine standardagainst which others may be observationally compared. It is acommon class K (K1) 4650 Kelvin orange giant, a "clump star" thatis quietly fusing its core helium into carbon and oxygen. At adistance of 117 light years, and with a luminosity 47 times that oftheSun and a radius 11 times solar, thestar's mass comes in at around double that of the Sun. About abillion years ago, just after its birth, it shone as a white classA star much like Sirius or Vega appear today. Not doing much atthe moment, the star will eventually run out of core helium, andwill begin to brighten as it prepares to eject its outer envelopeand become a white dwarf. For now, it can just be admired as apeaceful star with no companion that is gradually moving away fromus at a modest 22 kilometers per second. Without stars like thisone as a benchmark, the other, more exciting ones, would be muchmore difficult to study.
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