Aldebaran is close enough to the ecliptic to be occulted by the Moon, and is presently only possible by the Moon, because the planets pass Aldebaran to the north. Such occultations occur when the Moons ascending node is near the autumnal (fall) 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. On March 11th - 12th, 509 AD, an astronomer in Athens named Hipparchus recorded an occultation of Aldebaran by the Moon. More than a millennium later in 1718, the English astronomer Edmond Halley, most famous for the comet named after him, calculated that this could not have happened unless Aldebaran was in a slightly different position in ancient times from its location in 1718. It was only a small discrepancy of a few arcminutes, but it was the first, post dark-age, evidence that the fixed stars in the sky actually move relative to each other. Not only is Aldebaran moving slowly across the background of distant stars, but it is also moving away from the Earth and our Solar System very rapidly – at 33.554 miles per second. Thats the fastest proper motion of any of the brightest stars and is enough to cover a light year every 5,600 years.
Posted on: Thu, 23 Jan 2014 19:25:26 +0000
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