I saw on a minaret's tip Aldebaran like a ruby aflame, then leisurely slip into the black horizon's bowl.
–  Halid by William Roscoe Thayer

This entry is primarily about Aldebaran, the brightest star in Taurus 'the Bull', a major¹  constellation in the Northern Hemisphere. Aldebaran refers to the big bright star, but technically this is known as Aldebaran A because there is an Aldebaran B which is a much smaller and dimmer star.

Aldebaran is a first magnitude variable orange  giant² star which is very distinctive. Thanks to its ruddy colouring and position among the stars which form Taurus' head, colloquially Aldebaran has earned the nickname 'the eye of the bull'. The Aldebaran system is binary  – Aldebaran B (catalogued Alpha Tauri B and GJ 171.1 B³) is a red dwarf of spectral type M2 V; this companion is far too dim to be seen unaided.

Aldebaran is about 30-40 times the mass of our own Sun, and around 65 light years⁵ distant. It is highly evolved, now beyond the main sequence. Although it appears among the open cluster known as The Hyades (Caldwell 41), a V-shape which forms the 'head' of the bull, Aldebaran is not a member of that group of stars. It is much closer to us but happens to lie in the same direction from our vantage point. If another marker is required to locate Aldebaran, find the three main stars of Orion's 'belt' (Alnitak, Alnilam, and Mintaka); Aldebaran is to the right (in the Northern Hemisphere), the next brightest star after Mintaka.

Ecliptic Occultations

Aldebaran is positioned just over 5° south of the ecliptic plane, the apparent path traced by the Sun across the sky during the course of a year⁶. As a result, Aldebaran is sometimes occulted by the Moon, that is, the Moon travels in front of Aldebaran, blocking out our view of it. It is one of very few bright stars for which this happens. Measurements taken at these times from various points on Earth can provide information for projects like mapping the Moon.

The Eye Moves

In March 509 AD, an astronomer in Athens 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 current location. It was only a small discrepancy, a few arcminutes, but it was the first 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 54 kilometres per second. That's the fastest motion of any of the really bright stars and is enough to cover a light year every 5,600 years. So in the distant past, Aldebaran was much closer to us – it is estimated that 320,000 years ago, it was only 22 light years from Earth. It would have been much brighter in our skies, outshining even Sirius. The Human Race had not yet left Africa at that point – did they look up in wonder at this orange star, the brightest in the sky?

Pre-history

The bull constellation is possibly the oldest in existence. In 1940 a reported 16,500-year-old painted bull was discovered on a cave wall at Lascaux in central France. Above the shoulder of the bull are markings which could represent the 'seven sisters', also known as Messier 45 or the Pleiades star cluster. If modern human's ancestors identified the whole constellation as a bull, then they probably recognised the angry flaring of the wild animal's eye in the outstandingly-coloured bright star.

Regal and Religious Star

The name we know the star by, Aldebaran, is of Arabian origin; it means 'the follower' (of the Pleiades). One of the four 'Royal Stars' of ancient Persian culture, their name for Aldebaran was Tascheter, Watcher of the East. Known to the Romans as Parilicium, the ancient Greeks and Egyptians also knew this star well. To the ancient Chinese the constellation wasn't a bull at all, but a white tiger, so Aldebaran was quite literally the eye of the tiger⁷.

Ancient Egyptian Astronomy

Astronomy was very important to ancient Egyptians; they thought the brightest stars were souls of dead pharaohs living on in the afterlife. Their astronomers divided the night sky into 36 'decans' (constellations or star groupings); we know some stars were more important to them than others because they acted as calendar markings. Rather than being the science it is for us today, their astronomy was ruled by religion and individual deities: Thoth was the god of wisdom and writing, and the inventor of astronomy. In one physical manifestation he is depicted as a squatting baboon with a lunar disc and crescent upon his head. Two such 15' (4.5m) statues weighing 35 tonnes each were carved and erected at Khmun (now el-Ashmunein) on the orders of 18th Dynasty Pharaoh Amenhotep III (1390 - 1352 BC), the father of Akhenaten and grandfather of Tutankhamun.

The Egyptians worshipped the sun god Ra, who according to them sailed across the sky each day in a celestial boat. In the evening Ra was swallowed by the goddess Nut, passed through her body during the night and was then reborn at sunrise. Another important deity was Osiris, the god of life, fertility and the Akhet (Inundation: the flooding of the Nile upon which all life in Egypt depended), and they identified Osiris in the heavens with the star pattern we know as Orion, the constellation adjoining Taurus. On the ceiling of a tomb in Luxor (ancient Thebes), a representation of the god Osiris (Orion) is portrayed in stars, as well as other nearby stars. The stars are painted white, with two exceptions: Aldebaran and Betelgeuse are depicted in red ochre.

Possible Companion Aldebaran Ab

In 1997 an object over 11 times the mass of Jupiter was reported by Hatzes and Cochran et al in orbit around Aldebaran, although the discovery has not yet been verified or published. Some astronomers think the aged star itself was pulsating, which created data similar to that which would indicate the presence of a close companion planet or brown dwarf (failed star).

Second 'Eye'

On the evening of the Winter Solstice, 21 December, 2012, Jupiter will come close to Aldebaran from our line of sight. It will look like the Bull has two bright glowing eyes, one white and one red. This might be considered an omen of sorts, but it's doubtful it signals the end of the world, like some conspiracy theorists claim – basing their projections on the fact that the Mayan calendar ends on the Winter Solstice of 2012.

Modern Culture

'2000 Light Years From Home' is a song written by Mick Jagger and Keith Richards. Some lyrics are: Seen you on Aldebaran, safe on the green desert sand, it's so very lonely, you're two thousand light years from home. It appears on the 1967 album Their Satanic Majesties Request by The Rolling Stones.

Aldebaran in Science Fiction

In the Star Trek universe a three-headed reptilian serpent-like creature hails from the Aldebaran system – the god-like entity 'Q' changed himself into one during an episode of The Next Generation. There is also a populated fictional planet, Aldebaran III, whose denizens produce and market the green Aldebaran whisky. As it is the 'real thing', as opposed to the synthehol usually served aboard the Enterprise-D, Guinan⁸ keeps bottles of the potent brew under the bar in Ten Forward especially for Captain Picard to imbibe. Data gave a bottle to 'Scotty' (Captain Montgomery Scott) after he complained that there was no alcohol on board the Enterprise-D. He drowned his sorrows with it on a holographic recreation of the bridge of the original Enterprise  – 'No bloody A, B, C or D.'