Aldebaran –
Aldebaran – Wikipedia, the free encyclopediaPhysical properties[edit]
Size comparison between Aldebaran and the Sun.
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 leading to core compression from gravity and helium fusion ignition through the triple-alpha fusion process.[9] Hydrogen fusion is now occurring in a shell around the helium core. The helium flash ignition expanded the star to a diameter of 44.2 times the diameter of the Sun,[4][10] 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.[3]
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.[2] With a near-infrared J band magnitude of -2.1,[1] only Betelgeuse (-2.9), R Doradus (-2.6), and Arcturus (-2.2) are brighter.
Visibility[edit]
Aldebaran is one of the easiest stars to find in the night sky, partly due to its brightness and partly due to its spatial relation to one of the more noticeable asterisms in the sky. If one follows the three stars of Orion‘s belt from left to right (in the Northern Hemisphere) or right to left (in the Southern), the first bright star found by continuing that line is Aldebaran.
Since the star is located (by chance) in the line of sight between the Earth and the Hyades, it has the appearance of being the brightest member of the more scattered Hyades open star cluster that makes up the bull’s-head-shaped asterism; however, the star cluster is actually more than twice as far away, at about 150 light years.
In this predawn occultation, Aldebaran has just reappeared on the dark limb of the waning crescent Moon (July 1997 still frame captured from video).
Aldebaran is close enough to the ecliptic to be occulted by the Moon. Such occultations occur when the Moon’s ascending node is near the autumnal equinox. This event will next occur around 2015. A reasonably accurate estimate for the diameter of Aldebaran was obtained during the September 22, 1978 occultation.[11] Aldebaran is in conjunction with the Sun around June 1 of each year.[
