Capella (star)

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Alhajoth, α Aurigae, 13 Aurigae, HR 1708, HD 34029, Gl 194, BD+45°1077, FK5 193, HIP 24608, SAO 40186, GC 6427, ADS 3841, CCDM J05168+4559

|} 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.

Contents

1 Physical characteristics

1.1 Capella's comparative luminosity

2 Cultural references

2.1 Alternative and former names
2.2 In fiction

3 References
4 External links

Physical characteristics

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.

Capella's comparative luminosity

The closest of all naked eye stars is Alpha Centauri, a distance of 1.35 parsecs from us. Capella is 14 parsecs distant from the Earth, or more than 10 times farther away than Alpha Centauri. Capella and Alpha Centauri appear equally bright in appearance, with the former having a apparent magnitude of 0.2 and the latter 0.1, respectively. The intensity of light decreases as the square of the distance. So the light of Capella has had an opportunity to diminish by 10 × 10 or 100 times more than Alpha Centauri. Remembering that Capella appears to the naked eye viewer to be as bright as Alpha Centauri, the star must be 100 times as bright in reality. Capella thus has an absolute magnitude of -0.6.

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").

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: Alhajoth ("Goat")
Hindu: Brahma Ridaya ("Heart of Brahma")
Inca: Colca
Latin: Amalthea, Hircus ("Goat")

In fiction

In the fictional Marvel Universe, the alien Badoon are natives of Capella II.

In the computer game Freespace 2, Capella is one of the core systems of the Galactic Terran Vasudan Alliance and is home to over 300 million Terrans. It is invaded by "Shivan" forces, and the star itself is destroyed.

The Star Trek episode "Friday's Child" is set on planet Capella IV.

References

Hummel, C. A., et al., 1994, AJ, 107, 1859
Fact and Fancy by Isaac Asimov, Discus/Avon Books, March 1972, pages 152-155.

External links

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

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