Capella (star)

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For other uses, see Capella.

Capella (α Aur / α Aurigae / Alpha Aurigae) is the brightest star in the constellation Auriga and sixth brightest star in the sky. Although it appears as a single point to the naked eye, Capella is actually a bright close binary pair of stars along side a second, fainter binary.

==Physical characteristics==Hi A yellow star, it traditionally marks the left shoulder of the constellation's eponymous charioteer, or sometimes the goat that the charioteer is carrying. It is closer to the north celestial pole than any other first magnitude star (Polaris is only second magnitude) and as a result has played a significant role in many mythological writings. A tablet dating back to 2000 BC refers to Capella.

Astronomically, Capella's interest lies in the fact that it is an easily-studied non-eclipsing spectroscopic binary star. These two giant G-class stars have luminosities of around 50 and 80 times that of the Sun and lie less than 100 million km apart with an orbital period of 104.02 days. The stars were probably of spectral class A during their main sequence, similar to Sirius, and are in the process of becoming red giants in a few million more years as they continue to expand, cool, and brighten. Capella is a source of X-rays, probably due to surface magnetic activity on one of the pair. The Capella binary was the first star system to be imaged using a long baseline optical astronomical interferometer in observations by COAST in 1995.

The central stars also have a faint companion that is itself a double star, consisting of two M-class red dwarf stars, that orbit at around a light year away from the main pair.

[edit] Capella's comparative luminosity

Comparing Capella to the nearest bright star, Alpha Centauri, Capella is of similar visual magnitude yet it is around 10 times further away. Since the intensity of light decreases as the square of the distance, Capella is therefore around 100 times the luminosity of Alpha Centauri.

[edit] Cultural references

The name Capella means 'little she goat' in Latin, as in Roman mythology the star represented the goat Amalthea that suckled Jupiter. It was this goat whose horn, after accidentally being broken off by Jupiter, was transformed into the Cornucopia, or "horn of plenty", which would be filled with whatever its owner desired.

In Hindu mythology, Capella was seen as the heart of Brahma. The star is also often labelled "the shepherd's star" in English literature.

Astrologically, Capella portends civic and military honors and wealth. In the Middle Ages, it was considered a Behenian fixed star with sapphire and thyme as attributes. Cornelius Agrippa listed its kabbalistic sign with the name Hircus (Latin, "goat").

[edit] Alternative and former names

Due to it brightess, Capella has had a name in several cultures.

• Akkadian: Dilgan Iku ("Messenger of Light"), Dilgan Babili ("Patron star of Babylon")
• Arabic: al-'Ayyuq العيوق (Alhajoth) ("Goat")
• Hindu: Brahmahridaya ("Heart of Brahma")
• Persian: Bozbān بزبان ("Goat-keeper"), Negahbān نگهبان ("Guard")
• Inca: Colca
• Latin: Amalthea, Hircus ("Goat")

It is known as 五车二 (Wǔjū'èr, the Second Star of the Five Chariots) in Chinese. Obviously, the ancient Chinese and the Greeks came up with the same idea that this constellation resembles the shape of a chariot.

[edit] See also

• Capella in fiction

[edit] References

• Hummel, C. A., et al., 1994, AJ, 107, 1859
• Fact and Fancy {Intriguing Speculations on the Possibilities of Science} by Isaac Asimov, Discus/Avon Books, March 1972, pages 152-155.

[edit] External links

• Images of the bright binary pair from 13 September 1995 and 28 September 1995 (note fainter blobs are just noise)