ZUBENESCHAMALI (Beta Librae). Pronounced, zoo-ben-es-sha-mali, this tongue
twister is among the better known of star names, along with that of
its partner Zubenelgenubi,
respectively the Beta and Alpha stars of
Libra, the Scales. The pair, the only modestly bright stars in
Libra, are still of only third magnitude (Beta coming in at
2.61). Libra is the only
constellation of the Zodiac -- the band of constellations
containing the Sun's path -- that is not a living thing, the term
Zodiac meaning "circle of animals." Appropriate to its name, Libra
once held the autumnal equinox (it no longer does because of
precession, the 26,000-year wobble of the Earth's axis). But
"Libra" is a more modern appellation, its two brigher stars once
representing (and of course still doing so) the outstretched claws
of Scorpius, the Scorpion. Indeed, the name Zubeneschamali, the
northern one of the two, comes from an Arabic phrase meaning "the
northern claw," that of the Alpha star meaning "the southern claw."
Zubeneschamali is a hot "main sequence" (hydrogen fusing)
class B (B8) dwarf star with
a surface temperature of close to 12,000 Kelvin, double that of the
Sun.
While such stars are normally considered blue-white in color,
Zubeneschamali has long had a reputation of being the only naked
eye star that oddly appears GREEN to the human eye. Others have
claimed that it merely appears white. No doubt the argument will
persist. From its distance of 160 light years, we calculate that
the star is about 130 times more luminous than the Sun. Its high
temperature makes for a simple spectrum (its rainbow of colors) and
it is therefore ideal for examining the medium of interstellar gas
and dust that like between us and the Sun. Like many stars of its
kind, it is spinning rapidly, over 100 times faster than the Sun.
Though not considered a variable star, ancient astronomers claimed
it to be as bright or brighter than first magnitude
Antares right
next door in Scorpius.
We will probably never know if that is
true, or, if it is, how Zubeneschamali could have faded so fast.