MENKALINAN (Beta Aurigae). Beautifully shaped Auriga, the Charioteer, rides high in
northern winter skies, dominated by brilliant Capella at the northwestern corner of
the prominent pentagon that makes the figure. Almost immediately to
the east lies a mid-second magnitude star, Menkalinan (Men-KAL-in-an),
at the northeast corner, the Arabic name meaning
"the shoulder of the rein-holder." Though the third brightest star
in the classic pentagon, Menkalinan carries Auriga's "Beta"
designation. The second brightest,
Elnath, close to first
magnitude, connects Auriga with Taurus, and though it has the
formal name Gamma Aurigae, is more properly known as Beta Tauri,
technically leaving Menkalinan second brightest in Auriga. As
Polaris locates the
North Celestial Pole and Mintaka in Orion's
Belt the celestial
equator, Menkalinan locates the "solstitial colure," the great
circle in the sky that passes through both celestial poles and the
summer and
winter solstices.
Immediately south lies Theta Aurigae,
while to the north is equally close
Delta Aur (who tells the full story).
A line passed through these three stars to the north points
to the North Celestial Pole, while to the
south it points at Betelgeuse in
Orion, the summer solstice (the location of the Sun on the first
day of summer) lying in Gemini
about half way between Theta and Betelgeuse. (
Pi Aurigae, just north of Menkalinan, adds nicely to the
line as well.) Menkalinan is a class
A star with a temperature of 9200 Kelvin, not very much different
from Vega or Sirius. From its distance of 82 light
years, we calculate a luminosity 95 times that of the
Sun, somewhat
brighter than a normal "A star" should be. Careful observation
reveals that every 3.96 days, the "star" undergoes a partial
eclipse of about a tenth of a magnitude, showing that it actually
consists of TWO almost identical stars in a tight orbit, each about
48 times more luminous than the Sun separated only about one-fifth
the distance between the Sun and Mercury. They may both be
"subgiants" that have begun to change and brighten as a result of
exhaustion of their core hydrogen fuel. They are so close that
they distort each other through mutual tides, neither of them
round. A faint red dwarf far below naked-eye vision appears to
orbit the pair at least 330 Earth-Sun distances away, from which
the bright pair would be just barely separable by eye.