VEGA

'Vega' (α Lyr / α Lyrae / Alpha Lyrae) is the brightest star in the constellation Lyra, the fifth brightest star in the sky and the second brightest star in the Northern celestial hemisphere, after Arcturus. It can often be seen near the zenith in the mid-northern latitudes during the evening in the Northern Hemisphere summer, and during these times from mid-southern latitudes it can be seen low above the northern horizon during the Southern Hemisphere winter.
It is a "nearby star" at only 24.3 light years from Earth, and together with Arcturus and Sirius, one of the brightest stars in the Sun's neighborhood. It is one of the stars in the Local Bubble.
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.
It is 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 lifetime 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^[1] 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.
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 micrometers.
The name Vega comes from the Arabic word ''waqi'' meaning "falling", via the phrase 'النسر الواقع' ''an-nasr al-wāqi‘'', translated "the swooping vulture". As the Lyra constellation was once considered a vulture not a lyre.
It is known as 织女星 (Zhìnǚxīng, the Star of the Weaver Girl) in Chinese, (See Qi Xi) and Vanand in Persian tradition.

Contents

Rapid rotation

Possible planetary system

Cultural significance

References

External links

Rapid rotation

From the Earth, Vega is seen from within 5 degrees of its polar (rotation) axis, but if viewed along the plane of its equator, Vega would look about 20% fainter than at the poles.^[2] 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 near 10,000 K (17,500 °F), while equatorial temperature is 7,600 K (13,200 °F).^[3]
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.

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.^[4]
Determining the nature of the planet has not been straightforward. A 2002 paper hypothesizes that the lumps are caused by a roughly Jupiter-mass planet on an eccentric orbit. ^[5]. A 2003 paper hypothesizes these lumps could be caused by a roughly Neptune-mass planet having migrated from 40 to 65 AU over 56 million years, ^[6] an orbit large enough to allow the formation of smaller rocky planets closer to Vega.^[7].
The habitable zone of Vega is centered around 7.1 AU. An Earthlike planet orbiting in the habitable zone will have an orbital period around 10.9 Earth years .

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.
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.

References

1. Peterson, Deane (2006). "Vega is a rapidly rotating star". ''Nature'' '13 April 2006'.
2. Gulliver, A. F., Hill, G., and Adelman, S. J. 1994, ''Astrophysical Journal Letters'', v. 429, pp. L81-L84. [1]
3. Peterson, Deane (2006). "Vega is a rapidly rotating star". ''Nature'' '13 April 2006' (preprint).
4. Joint Astronomy Centre, Hilo (April 21, 1998). ★ class=wikiexternal target=_blank>-http%3A//outreach.jach.hawaii.edu/pressroom/1998_vega ''Astronomers discover possible new Solar Systems in formation around the nearby stars Vega and Fomalhaut.'' Press Release.
5. Wilner, D., Holman, M., Kuchner, M., & Ho, P.T.P. (2002). "Structure in the Dusty Debris around Vega". "The Astrophysical Journal" '569', L115-L119. (Abstract)
6. Wyatt, M. (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)
7. The Royal Observatory, Edinburgh (December 1, 2003). ''New evidence for Solar-like planetary system around nearby star.'' Press Release.

External links

★ Vega

★ Coronagraphic Search for Extra-Solar Planets around epsilon Eri and Vega

★ Sir Harry Kroto, NL presents 8 Astrophysical Lectures including discussion of Vega Freeview videos provided by the Vega Science Trust.