ARCTURUS (Alpha Bootes) is the brightest star of the northern
hemisphere and the fourth brightest star of the entire sky, following
only Sirius, Canopus, and Alpha Centauri. Arcturus is located at a
distance of 37 light years, It is a classic orange giant star with a
precisely defined surface temperature of 4290 degrees Kelvin. Taking
infrared radiation into account, it shines 180 times more brightly than
our Sun, from which we find a diameter 24.5 times solar, about a quarter
the size of Mercury's orbit.
Arcturus is close and large enough so that its angular diameter
of 0.0191 seconds of arc can easily be measured, leading to a direct
determination of 23 times the solar dimension and providing nice
confirmation of stellar parameters. Arcturus has a velocity
somewhat higher than other bright stars, and comes from a somewhat older
population of the Galaxy. Consistently, it is somewhat deficient in
metals, having only about 20 percent as much iron relative to hydrogen as
found in the Sun. As a giant, weighing in at around 1.5 times the mass of
the Sun, it has ceased the fusion of hydrogen in its core.
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