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TARAZED

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 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 "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.