TARAZED (Gamma Aquilae). One of the minority of stars that does
not have an Arabic-derived name, "Tarazed" comes to us from a
Persian phrase meaning "the Beam of the Scale," and was originally
applied to the star Altair and its two
flanking stars, bright third
magnitude (2.72) Tarazed and fourth magnitude
Alshain, as together they
look like a weighing balance. In our constellation lore, the trio
are the most prominent part of Aquila,
the Eagle, which flies
through a bright part of the Milky Way between Cygnus (the Swan) to
the north and Sagittarius to the south.
Though Tarazed was placed
by Bayer in the Eagle's back, it and Alshain together surely more
remind one of the great bird's outstretched wings. Though Tarazed
is by far the second brightest star in the constellation, Bayer
still gave it the Gamma designation, fainter Alshain becoming the
Beta star. Tarazed is a class K (K3) bright
giant, a fairly cool
(4100 Kelvin) luminous star that falls between the classical, more
ordinary, giants and the supergiants. Its distance of 460 light
years leads to a luminosity (accounting for invisible infrared
radiation from the cool surface) 2960 times that of the Sun, and
these to a radius of 110 solar. A true giant half an Astronomical
Unit across, if the star were our Sun it would extend halfway to
the orbit of the Earth and appear 60 degrees across in our sky,
two-thirds of the way from the horizon to the point overhead. It is so
large that it can be detected as a disk with an angular diameter of
0.0075 seconds of arc, which with the distance gives the same
physical diameter as above, showing all the measures to be quite
accurate. Tarazed is a source of X-rays, and is a rare "hybrid"
star rather like Sadalmelik (Alpha
Aquarii) that has
characteristics of both luminous giants with cool winds and less
luminous ones that have hot outer layers more like Sun. Its
luminosity and temperature suggest a mass about five times solar.
Though only a little over 100 million years old, the star is probably
already fusing helium into carbon in its core, the core
ultimately to be come a
white dwarf something like the companion to
Sirius. Dedicated to the memory of Daniel
Edward Malcolm Leggett, who loved the stars.