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Aldebaran
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Aldebaran ( a Tau, a Tauri, Alpha Tauri) is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. Because of its location in the head of Taurus, it has historically been called the Bull's Eye. Aldebaran has the appearance of being the brightest member of the more scattered Hyades cluster, which is the closest star cluster to Earth. However, it is merely located in the line of sight between the Earth and the Hyades, and is actually an independent star.
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Encyclopedia
Aldebaran ( a Tau, a Tauri, Alpha Tauri) is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. Because of its location in the head of Taurus, it has historically been called the Bull's Eye. Aldebaran has the appearance of being the brightest member of the more scattered Hyades cluster, which is the closest star cluster to Earth. However, it is merely located in the line of sight between the Earth and the Hyades, and is actually an independent star. NASA's Pioneer 10 spacecraft, which flew by Jupiter in 1973 will reach and pass by Aldebaran in about two million years.
In 1997, a possible substellar companion was reported, with a mass at least 11 times that of Jupiter with an orbital period of around 2 years; however, this has not been confirmed.
Physical properties
Aldebaran is a K5III star, which means it is orangish, large, and has moved off the main sequence after exhausting the hydrogen fuel in its core. It has a minor companion (a dim M2 dwarf orbiting at several hundred AU). Now primarily fusing helium, the main 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 away, and it shines with 150 times the Sun's luminosity. With an apparent magnitude of 0.87, it is the 13th brightest star. It is slightly variable, of the irregular variable type, by about 0.2 magnitude.
Radial velocity variations
In 1993, radial velocity measurements of Aldebaran A, Arcturus and Pollux showed that Aldebaran A exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion with a minimum mass 11.4 times that of Jupiter in a 643-day orbit at a separation of 2.0 AU in a mildly eccentric orbit. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion. On the other hand, it should be noted that the companion to the star Pollux postulated in the 1993 paper has since been confirmed (see Pollux b).
Further analysis of the spectrum of Aldebaran A did not show any variation correlated to the 643-day radial velocity oscillation, which would be expected if the cause was intrinsic. The best orbital solution was found to be around 653.8 days with an eccentricity of 0.182, and a lower mass limit of 11 Jupiter masses. The high value for the minimum mass means that it is likely that the object, if it exists, exceeds 13 Jupiter masses and is therefore a brown dwarf. However it is possible that the oscillation is due to a combination of pulsations, and , this companion has not been confirmed.
Visibility
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.
This star 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, as will be the case around 2015.
Etymology and cultural significance
The name Aldebaran comes from the Arabic ( ) meaning "the follower" and refers to the way the star follows the Pleiades star cluster in its nightly journey across the sky. In Persia it was known as Sadvis and Kugard. The Romans called it , and it is known as (, the Fifth Star of the Net) in Chinese. Aldebaran is identified as the lunar mansion Rohini in Hindu astronomy and as one of the twenty-seven daughters of Daksha and the wife of the god Chandra.
For the Dakotas (a branch of the Native American Sioux tribe), Aldebaran took on a heroic aspect. The young star was the child of the sun and the lady Blue Star. One day, he desired to hunt the white buffalo (the Pleiades). After he pulled up a sapling to make a spear, a hole was made in the ground and he could see all the people of Earth down below. The white buffalo took this chance to push him through. He was found by an old woman and was to be known as Old Woman's Grandson. On Earth, he killed many strange monsters that had been troubling the Native Americans; one monster of which was a serpent that caused drought. The young hero killed the serpent, releasing a great stream of water that became the Mississippi River. In time, Old Woman's Grandson remembered the white buffalo and returned to hunting him in the sky to fulfill his destiny.
For the Seris of northwestern Mexico, this star is providing light for the seven women giving birth (Pleiades). It has three different names: , , and ("star that goes ahead"). The lunar month corresponding to October is called "Aldebaran's path".
In Inuit astronomy, Aldebaran is called "Spirit of a Polar Bear".
In the religion of Stregheria, Aldebaran is a fallen angel and quarter guardian of the eastern gate.
Aldebaran is referenced in Edmund Spenser's The Faerie Queene, (1590) book one, canto three, stanza 16:
Now when Aldeboran was mounted hye/
Aboue the shinie Cassiopeia chaire (I.III.16.1-2)
See also
External links
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