Capella (star)

Capella (α Aur / α Aurigae / Alpha Aurigae) is the brightest star in the constellation Auriga and sixth brightest star in the sky.

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 bright star (Polaris is quite dim by comparison) and as a result has played a significant role in many mythological writings. A tablet dating back to 2000 BC refers to Capella. Astrologically, Capella portended civic and military honors and wealth.

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. Capella is a source of X-rays, probably due to surface magnetic activity on one of the pair. Capella was the first star to be imaged using a long baseline optical 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.

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.

Facts

• Right ascension (J2000): 5h 16m 41.4s
• Declination (J2000): +45° 59' 53"
• Distance from Earth: 42.2 light years
• Parallax: 77.29 ± 0.89 mas
• Apparent visual magnitude: 0.08
• Absolute visual magnitude: −0.5
• Spectral type: G5IIIe+G0III
• Mass: 2.5 Solar masses

Alternative and former names

• Akkadian: Dil-gan I-ku, "Messenger of Light", or Dil-gan Babill, "Patron star of Babylon"
• Arabic: Alhajoth, "Goat"
• Hindu: Brahma Ridaya, "Heart of Brahma"
• Inca: Colca
• Roman: Amalthea

Alternative catalogue names include Flamsteed 13 Aurigae; HD 34029; HR 1708