A cool red giant star, prominently located in the constellation Taurus. With its red color, it appropriately represents the eye of the Bull. At a distance of 18.5 parsecs (60 light-years), Aldebaran, or α Tauri, is among the nearest (and brightest) giant stars to the Sun. It appears to be situated near the middle of the Hyades, but Aldebaran is actually less than half the distance of this nearby star cluster. The star is an example of a K-type giant, a very common type of evolved star that derives its energy from the thermonuclear burning of helium in a core surrounded by a thin, hydrogen-burning shell. Its spectral type of K5III corresponds to an effective temperature of 6700°F (4000 K) and a radius of about 40 times the Sun. It is nearly 150 times more luminous than the Sun and, as is typical for K giants, its brightness varies by a modest amount. Aldebaran is accompanied in a long-period binary-star system by a cool dwarf companion star some 100,000 times fainter than the giant.