Physical Properties
Aldebaran is classified as a type K5III star. It is an orange giant star that has moved off the main sequence line of the Hertzsprung–Russell diagram. It has exhausted the hydrogen fuel in its core and hydrogen fusion has ceased there. Although not yet hot enough for fusing helium, the core temperature of the star has greatly increased due to gravitational pressure and the star has expanded to a diameter of 44.2 times the diameter of the Sun, approximately 61 million kilometres (see 10 gigametres for similar sizes). The Hipparcos satellite has measured it as 65.1 light years (20.0 pc) away, and it shines with 425 times the Sun's luminosity.
Aldebaran is a slightly variable star, of the slow irregular variable type LB. It varies by about 0.2 in apparent magnitude from 0.75 to 0.95. With a near-infrared J band magnitude of -2.1, only Betelgeuse (-2.9), R Doradus (-2.6), and Arcturus (-2.2) are brighter.
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