Capella (star)
From Wikipedia, the free encyclopedia
 Capella is the brightest star in Auriga |
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation (pronunciation) |
Auriga |
| Right ascension | 05h 16m 41.4s |
| Declination | +45° 59' 53" |
| Apparent magnitude (V) | +0.08 +0.71/+0.96 |
| Characteristics | |
| Spectral type | G8III / G0III |
| U-B color index | +0.45 |
| B-V color index | +0.80 / −0.25 |
| Variable type | RS CVn |
| Astrometry | |
| Radial velocity (Rv) | 30.2 km/s |
| Proper motion (μ) | RA: 75.52 mas/yr Dec.: −427.13 mas/yr |
| Parallax (π) | 77.29 ± 0.89 mas |
| Distance | 42.2 ± 0.5 ly (12.9 ± 0.1 pc) |
| Absolute magnitude (MV) | −0.5 +0.14/+0.29 |
| Details | |
| Mass | 2.69/2.56 M☉ |
| Radius | 10.2/8.5 R☉ |
| Luminosity | 78.5/77.6 L☉ |
| Temperature | 5270/5900 K |
| Metallicity | 40% Sun |
| Age | ? years |
| Visual binary orbit | |
| Companion | Capella Ab |
| Period (P) | 0.284802 ± 0.000005 yr |
| Semimajor axis (a) | 0.05647 ± 0.00005" |
| Eccentricity (e) | 0.0000 ± 0.0002 |
| Inclination (i) | 137.18 ± 0.05° |
| Longitude of the node (Ω) | 40.8 ± 0.1° |
| Periastron epoch (T) | 1989.00329 ± 0.00005 |
| Other designations | |
| Database references | |
| SIMBAD | Capella A data |
| Database references | |
| SIMBAD | Capella B data |
Capella (α Aur / α Aurigae / Alpha Aurigae) is the brightest star in the constellation Auriga and eleventh 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 yellow giant stars alongside a second, fainter binary.
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[edit] System
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 70 times the luminosity of Alpha Centauri.
[edit] Etymology and cultural significance
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").
In Persian literature, Capella (Bozbān, Ayyuq) is a metaphor for a huge distance and also the light red colour.
In Australian Aboriginal mythology, Capella was Purra, the kangaroo, pursued and killed by the nearby Gemini twins or by the Orion hunter,[1][2][3] or near the Orion belt twins canoe.[4]
To the Bedouin people of the Negev and Sinai, Capella is known as al-'Ayūg, 'the dandy', in its role as pointing out the position of the Pleiades -its name more fully al-'Ayūg ath-Thurayyā 'dandy of the Pleiades'.[5]
[edit] Alternative and former names
Due to its brightness, Capella has had a name in several cultures.
- 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")
- Hawaiian: Hokulei ("Star-Wreath")
- Chinese: Wǔjū'èr 五车二 ("Second Star of the Five Chariots")
[edit] See also
[edit] References
- ^ http://www.atnf.csiro.au/research/AboriginalAstronomy/literature/Stanbridge1857.pdf
- ^ Australian Zodiac
- ^ http://www.atnf.csiro.au/people/rnorris/SydneyRockArt/sites/TerreyHillsHunt/mosaic.jpg
- ^ http://www.brandlehner.at/Brandlehner/c2picture.nsf/pictures/CBRR-6FGLDF/$File/CBRR-6FGLDF.jpg
- ^ Bailey, Clinton (1974). "(abstract) Bedouin Star-Lore in Sinai and the Negev" (abstract). Bulletin of the School of Oriental and African Studies, University of London 37 (3): 580-96.
- 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)
- Capella Returns to Northern Sky, Points Way to Comet
