Vega: Difference between revisions

 

==Nomenclature==

[[File:LyraCC.jpg|thumb|left|upright|Vega is the brightest star in the constellation of Lyra.]]

''[[α]] Lyrae'' ([[Latinisation of names|Latinised]] to ''Alpha Lyrae'') is the star's [[Bayer designation]]. The traditional name ''Vega'' (earlier ''Wega''<ref name=allen1963/>) comes from a loose transliteration of the [[Arabic]] word ''{{transliteration|ar|wāqi'}}'' ([[Arabic]]: <big>واقع</big>) meaning "falling" or "landing", via the phrase ''{{transliteration|ar|an-nasr al-wāqi'}}'' ([[Arabic]]: <big>النّسر الْواقع</big>), "the falling eagle".<ref name=glasse2008/> In 2016, the [[International Astronomical Union]] (IAU) organized a [[Working Group on Star Names]] (WGSN)<ref name="WGSN"/> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1"/> included a table of the first two batches of names approved by the WGSN; which included ''Vega'' for this star. It is now so entered in the [[IAU Working Group on Star Names|IAU Catalog of Star Names]].<ref name="IAU-CSN"/>

 

==Observation==

[[Image:Summer triangle.png|left|thumb|upright=1.2|The [[Summer Triangle]]]]

Vega can often be seen near the [[zenith]] in the mid-northern [[latitude]]s during the evening in the [[Northern Hemisphere]] summer.<ref name=pasachoff2000/> From mid-southern latitudes, it can be seen low above the northern horizon during the [[Southern Hemisphere]] winter. With a [[declination]] of +38.78°, Vega can only be viewed at latitudes north of [[51st parallel south|51° S]]. Therefore, it does not rise at all anywhere in [[Antarctica]] or in the southernmost part of South America, including [[Punta Arenas]], [[Chile]] (53° S). At latitudes to the north of [[51st parallel north|51° N]], Vega remains continuously above the horizon as a [[circumpolar star]]. Around July 1, Vega reaches midnight [[culmination]] when it crosses the [[Meridian (astronomy)|meridian]] at that time.<ref name=burnham1978/> Complementarily, Vega swoops down and kisses the horizon at true North at midnight on Dec 31/Jan 1, as seen from 51° N. [[File:Path of Vega at winter solstice.png|thumb|Path of Vega at winter solstice, as seen from 51°N ]]

 

[[File:Vega by Stephen Rahn.jpg|thumb|Astrophoto of Vega]]

[[File:The first image of Vega.jpg|left|thumb|upright=1.2|"On the night of July 16–17, 1850, [[John Adams Whipple|Whipple]] and [[William Cranch Bond|Bond]] made the first [[daguerreotype]] of a star (Vega)"]]

[[Astrophotography]], the [[photography]] of celestial objects, began in 1840 when [[John William Draper]] took an image of the [[Moon]] using the [[daguerreotype]] process. On 17 July 1850, Vega became the first star (other than the Sun) to be photographed, when it was imaged by [[William Cranch Bond|William Bond]] and [[John Adams Whipple]] at the [[Harvard College Observatory]], also with a daguerreotype.<ref name=allen1963/><ref name=barger_white2000/><ref name=pasp2_10_249/> In August 1872, [[Henry Draper]] took a photograph of Vega's [[Astronomical spectroscopy|spectrum]], the first photograph of a star's spectrum showing absorption lines.<ref name=paps24_166/> Similar lines had already been identified in the spectrum of the Sun.<ref name=aip/> In 1879, [[William Huggins]] used photographs of the spectra of Vega and similar stars to identify a set of twelve "very strong lines" that were common to this stellar category. These were later identified as lines from the Hydrogen [[Balmer series]].<ref name=klaus2002/> Since 1943, the [[stellar spectrum|spectrum]] of this star has served as one of the stable anchor points by which other stars are classified.<ref name=baas25_1319/>

 

 

===Rotation===

Vega has a rotation period of 16.3 hours,<ref name=petit2022/> much faster than the Sun's rotational period but similar to, and slightly slower than, those of [[Jupiter]] and [[Saturn]]. Because of that, Vega is significantly [[oblate spheroid|oblate]] like those two planets.

 

When the radius of Vega was measured to high accuracy with an [[Astronomical interferometer|interferometer]], it resulted in an unexpectedly large estimated value of {{val|2.73|0.01}} times the [[radius of the Sun]]. This is 60% larger than the radius of the star Sirius, while stellar models indicated it should only be about 12% larger. However, this discrepancy can be explained if Vega is a rapidly rotating star that is being viewed from the direction of its pole of rotation. Observations by the [[CHARA array]] in 2005–06 confirmed this deduction.<ref name=apj645_1_664/>

[[File:Vega compared with the Sun.jpg|thumb|Size comparison of Vega (left) to the Sun (right)]]

The pole of Vega—its axis of rotation—is inclined no more than five degrees from the line-of-sight to the Earth. At the high end of estimates for the [[stellar rotation|rotation]] velocity for Vega is {{val|236.2|3.7|u=km/s}}<ref name=apj708_1_71/> along the equator, much higher than the observed (i.e. [[projected rotational velocity|projected]]) rotational velocity because Vega is seen almost pole-on. This is 88% of the speed that would cause the star to start breaking up from [[Centrifugal force|centrifugal]] effects.<ref name=apj708_1_71/> This rapid rotation of Vega produces a pronounced equatorial bulge, so the radius of the equator is 19% larger than the polar radius, compared to just under 11% for Saturn, the most oblate of the Solar System's planets. (The estimated polar radius of this star is {{val|2.362|0.012}} [[solar radius|solar radii]], while the equatorial radius is {{val|2.818|0.013}} solar radii.<ref name=apj708_1_71/>) From the Earth, this bulge is being viewed from the direction of its pole, producing the overly large radius estimate.

 

 

==Possible planetary system==

{{OrbitboxPlanet begin

| name = Vega

| first1=Gay Yee | display-authors=1 | last1=Hill | first2=Dolores | last2=Beasley | date=2005-01-10 | title=Spitzer Sees Dusty Aftermath of Pluto-Sized Collision | publisher=NASA/Spitzer Space Telescope | url=http://www.spitzer.caltech.edu/Media/releases/ssc2005-01/release.shtml | access-date=2007-11-02 | archive-url = https://web.archive.org/web/20070518105642/http://www.spitzer.caltech.edu/Media/releases/ssc2005-01/release.shtml| archive-date = May 18, 2007}}

 

{{Stars of Lyra}}

{{2021 in space}}