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.