Vega

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For other uses: see Vega (disambiguation)

**Vega**
Observation data Epoch J2000.0
Image:Vega Spitzer.jpg Vega as seen by the Spitzer space telescope
Constellation	Lyra
Right ascension	18^h 36^m 56.3^s
Declination	+38° 47' 01"
Apparent magnitude (V)	0.03
Characteristics
Spectral type	A0V
B-V color index	0.00
U-B color index	−0.01
Variable type	Delta Scuti
Astrometry <tr valign=top><td>Radial velocity (R_v)</td><td>−13.5 km/s</td></tr><tr valign=top><td>Proper motion (μ)</td><td> RA: 201.02 mas/yr Dec.: 287.46 mas/yr </td></tr><tr valign=top><td>Parallax (π)</td><td>129.01 ± 0.52 mas</td></tr><tr valign=top><td>Distance</td><td>25.27 ly (7.751 pc)</td></tr><tr valign=top><td>Absolute magnitude (M_V)</td><td>0.58</td></tr>
Details
Mass	2.6 M_☉
Radius	2.73 R_☉
Luminosity	51 L_☉
Temperature	9,300 K
Metallicity	63%
Rotation	12.5 h
Age	3.5 × 10⁸ years
Other designations
Alpha Lyrae, α Lyrae, 3 Lyr, GJ 721, HR 7001, BD +38°3238, HD 91262, GCTP 4293.00, LTT 15486, SAO 67174, HIP 91262

Vega (α Lyr / α Lyrae / Alpha Lyrae) is the brightest star in the constellation Lyra, and the fifth brightest star in the sky. It is the third brightest star in the Northern night sky, after Sirius and Arcturus, and can often be seen near the zenith in the mid-northern latitudes during the Northern Hemisphere summer.

It is a "nearby star" at only 25.3 light years from Earth, and together with Arcturus and Sirius, one of the brightest stars in the Sun's neighbourhood.

Vega is a vertex of the Summer Triangle, which consists of Vega (in Lyra), Deneb (in Cygnus) and Altair (in Aquila). If one is to consider this asterism a right triangle, then Vega would correspond to its right angle. This triangle is very recognisable in the northern skies for there are few bright stars in its vicinity.

Its spectral class is A0V (Sirius, an A1V, is slightly less powerful) and it is firmly in the main sequence, fusing hydrogen to helium in its core. Since more powerful stars use their fusion fuel more quickly than smaller ones, Vega's life time is only one billion years, a tenth of our Sun's. Vega's current age is between 200 and 500 million years. Vega is twice as massive<ref>↑ Peterson, Deane (2006). "Vega is a rapidly rotating star". Nature 13 April 2006.</ref> as our Sun and burns at fifty times the power.

In about AD 14,000, Vega will become the North Star, owing to the precession of the equinoxes. See Polaris for more information.

Professional astronomers have used Vega for the calibration of absolute photometric brightness scales. When the magnitude scale was fixed, Vega happened to be close to zero magnitude. Therefore the visual magnitude of Vega was decided to be, by definition, zero at all wavelengths for many years (this is no longer the case, as the apparent magnitude zero point is now most commonly defined in terms of a particular numerically specified flux). It also has a relatively flat electromagnetic spectrum in the visual region (wavelength range 350-850 nanometers, most of which can be seen with the human eye), so the flux densities are roughly equal, 2000-4000 Jy. The flux density of Vega drops rapidly in the infrared, and is near 100 Jy at 5 micrometres.

The name Vega comes from the Arabic word waqi meaning "falling", via the phrase النسر الواقع an-nasr al-wāqi‘, translated "the swooping eagle". As part of the constellation Lyra it represents a jewel set in the body of the harp.

It is known as 织女星 (Zhìnǚxīng, the Star of the Weaver Girl) in Chinese. See Qi Xi.

1 Rapid rotation
2 Possible planetary system
3 Cultural significance
4 Alternative and former names
5 References
6 External links

[edit] Rapid rotation

From the Earth, Vega is seen from within 5 degrees of the polar (rotation) axis, but if it was viewed along the plane of the equator, Vega would look about 20% fatter at the equator than at the poles. This is because the star rotates at 93% of the speed that would cause it to start breaking up from centrifugal effects (with a rotation period of about 12.5 hours). The local gravitational acceleration at the poles is greater than at the equator so the local luminosity is higher (Von Zeipel theorem). This is seen as a variation in effective temperature over the star: polar temperature is 10,000 K (17,500 °F), while equatorial temperature is 7,600 K (13,200 °F).<ref>Peterson, Deane (2006). "Vega is a rapidly rotating star". Nature 13 April 2006 (preprint).</ref>

Astronomers are recalculating what the temperature would be for potential planets. A planet in a polar orbit around Vega would have a higher surface temperature than one in an equatorial orbit.

[edit] Possible planetary system

Vega has a disk of dust and gas around it, discovered by the IRAS satellite in the mid 1980s. This was initially thought to be a protoplanetary disk, but is now considered a "debris disk" due to the star's relatively young age of between 200 and 500 million years. In 1998 teams at the Joint Astronomy Centre and UCLA detected irregularities in it that suggest the presence of a planet.<ref>Joint Astronomy Centre, Hilo (April 21, 1998). Astronomers discover possible new Solar Systems in formation around the nearby stars Vega and Fomalhaut. Press Release.</ref> A 2003 paper hypothesizes these lumps could be caused by a Neptune-sized planet having migrated from 40 to 65 AU over 56 million years<ref>Wyatt, Mark (2003). "Resonant Trapping of Planetesimals by Planet Migration: Debris Disk Clumps and Vega's Similarity to the Solar System". The Astrophysical Journal 598, 1321-1340. (Abstract)</ref>, an orbit large enough to allow the formation of smaller rocky planets closer to Vega.<ref>The Royal Observatory, Edinburgh (December 1, 2003). New evidence for Solar-like planetary system around nearby star. Press Release.</ref> These findings have yet to be fully confirmed, but since Vega is much more powerful than our Sun, scientists believe there is no life possible on any such suggested planets.

[edit] Cultural significance

The star has been the subject of many 'firsts' in Astronomy; in 1850 it became the first star to be photographed, and in 1872 the first to have its spectrum photographed. It was also debatably the first star to have its parallax measured, in the pioneering experiments of Friedrich Struve in 1837. Finally, it became the first star to have a car named after it, when Chevrolet launched the 'Vega' in 1971.

In Chinese mythology, there is a love story of Qi Xi 七夕 in which Niu Lang 牛郎 (Altair) and his two children (β and γ Aquilae) are separated forever from their mother Zhi Nü 織女 (Vega) who is on the far side of the river, the Milky Way 銀河. The Japanese Tanabata festival is also based on this legend.

In Hindu astronomy, Vega is called Abhijit.

Medieval astrologers counted Vega as one of the Behenian stars and related it to chrysolite and winter savory. Cornelius Agrippa listed its kabbalistic sign under Vultur cadens, a literal Latin translation of the Arabic name.

See also: Vega in fiction

[edit] Alternative and former names

Original name in Arabic: An-Nasr Al-Wāqi‘, "The Falling Eagle" or "The Swooping Eagle"
Wega (a closer transliteration of the Arabic)
"The Harp Star" ("Harp" is the English word for Latin "Lyra")
Akkadian: Tir-anna, "Life of Heaven"
Babylonian: Dilgan, "the Messenger of Light"
Chinese: Zhi Nü, "the Weaver"
Greek: Allore
Sanskrit: Abhijit, "Victorious"
Latin: Fidis, "Lyre"; Vultur cadens, "Falling vulture"