ALDEBARAN (Alpha Tauri). Aldebaran is by far the brightest, and therefore the
Alpha, star of the constellation
Taurus. The ancient name, from
Arabic, means "the Follower," as the star seems to follow the
Pleiades, or Seven Sisters star cluster, across the sky.
Aldebaran, 60 light years away, is positioned in front of the
sprawling Hyades
star cluster (in mythology, half-sisters to the
Pleiades) that make the face of Taurus the Bull, but is not a part
of it, the cluster over twice as far away. In most renderings of
the constellation, Aldebaran makes the celestial Bull's eye. As
part of a constellation of the zodiac, Aldebaran is close to the
Sun's path, the Sun passing to the north of it about June 1, the
star also regularly covered, or occulted, by the Moon. This class
K star, of first magnitude and 13th brightest in the sky, is a low-
level irregular variable star that fluctuates erratically and to
the eye unnoticeably by about two-tenths of a magnitude.
Aldebaran's surface temperature of just under 4000 degrees Kelvin
(compared to the Sun's 5800 degree
temperature) gives it a distinct
orangy color. It is a giant star, a star in an advanced state of
evolution in which the interior hydrogen fuel has run out, the star
now running on the fusion of helium into carbon. Some 350 times
more luminous than the Sun, it has expanded to a radius about 40
times solar, making it big enough to enable astronomers to measure
its small angular diameter of only 0.021 seconds of arc (the
apparent size of a US nickel seen at a distance of 50 kilometers).
This large star is an extremely slow rotator, taking almost two
years to make a full spin. If placed at the position of the Sun,
Aldebaran would extend halfway to the planet Mercury and would
appear 20 degrees across in our sky, making life on Earth quite
impossible. Yet Aldebaran may have its own "solar system."
Recent, though still-unconfirmed, observations show that the star
may be slightly shifting back and forth in response to a small body
with a mass at least 11 times that of Jupiter and a two-year
orbital period. We do not yet know if the body -- if it exists at
all -- is a massive planet or a low-mass "brown dwarf," a failed
star that is too small to run supporting thermonuclear reactions in
its core.