Vega
Overview
 
Vega is the brightest star in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Lyra
Lyra
Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...

, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

, after Arcturus. It is a relatively close star at only 25 light-years from Earth, and, together with Arcturus and Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

, one of the most luminous stars in the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's neighborhood.

Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun." Vega was the northern pole star
Pole star
The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

 around 12,000 BC and will be so again around AD 13,727 when the declination will be +86°14'.
Encyclopedia
Vega is the brightest star in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Lyra
Lyra
Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...

, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

, after Arcturus. It is a relatively close star at only 25 light-years from Earth, and, together with Arcturus and Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

, one of the most luminous stars in the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's neighborhood.

Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun." Vega was the northern pole star
Pole star
The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

 around 12,000 BC and will be so again around AD 13,727 when the declination will be +86°14'. Vega was the first star other than the Sun to be photographed
Astrophotography
Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photographs of an astronomical object were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for...

 and the first to have its spectrum
Astronomical spectroscopy
Astronomical spectroscopy is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other celestial objects...

 recorded. It was one of the first stars whose distance was estimated through parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...

 measurements. Vega has served as the baseline for calibrating the photometric
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...

 brightness scale, and was one of the stars used to define the mean values for the UBV photometric system
UBV photometric system
UBV photometric system, also called the Johnson system , is a wide band photometric system for classifying stars according to their colors. It is the first known standardized photoelectric photometric system. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are...

.

Vega is only about a tenth of the age of the Sun, but since it is 2.1 times as massive its expected lifetime is also one tenth of that of the Sun; both stars are at present approaching the midpoint of their life expectancies. Vega has an unusually low abundance of the elements with a higher atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 than that of helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

. Vega is also a suspected variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...

 that may vary slightly in magnitude in a periodic manner. It is rotating
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....

 rapidly with a velocity of 274 km/s at the equator. This is causing the equator to bulge outward because of centrifugal effects, and, as a result, there is a variation of temperature across the star's photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

 that reaches a maximum at the poles. From Earth, Vega is being observed from the direction of one of these poles.

Based on an observed excess emission of infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 radiation, Vega appears to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk
Debris disk
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a...

, which is analogous to the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...

 in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. Stars that display an infrared excess because of dust emission are termed Vega-like stars. Irregularities in Vega's disk also suggest the presence of at least one planet, likely to be about the size of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

, in orbit around Vega.

Observation history

Astrophotography
Astrophotography
Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photographs of an astronomical object were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for...

, the photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

 of celestial objects, began in 1840 when John William Draper
John William Draper
John William Draper was an American scientist, philosopher, physician, chemist, historian, and photographer. He is credited with producing the first clear photograph of a female face and the first detailed photograph of the Moon...

 took an image of the Moon using the daguerreotype
Daguerreotype
The daguerreotype was the first commercially successful photographic process. The image is a direct positive made in the camera on a silvered copper plate....

 process. On July 17, 1850, Vega became the first star (other than the Sun) to be photographed, when it was imaged by William Bond
William Cranch Bond
William Cranch Bond was an American astronomer, and the first director of Harvard College Observatory.- Upbringing :William Cranch Bond was born in Falmouth, Maine on September 9, 1789...

 and John Adams Whipple
John Adams Whipple
John Adams Whipple was an American inventor and early photographer. He was the first in the United States to manufacture the chemicals used for daguerreotypes; he pioneered astronomical and night photography; he was a prize-winner for his extraordinary early photographs of the moon; and he was the...

 at the Harvard College Observatory
Harvard College Observatory
The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...

, also with a daguerreotype. Henry Draper
Henry Draper
Henry Draper was an American doctor and amateur astronomer. He is best known today as a pioneer of astrophotography.-Life and work:...

 took the first photograph of a star's spectrum
Astronomical spectroscopy
Astronomical spectroscopy is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other celestial objects...

 in August 1872 when he took an image of Vega, and he also became the first person to show absorption lines in the spectrum of a star. Similar lines had already been identified in the spectrum of the Sun. In 1879, William Huggins
William Huggins
Sir William Huggins, OM, KCB, FRS was an English amateur astronomer best known for his pioneering work in astronomical spectroscopy.-Biography:...

 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
Balmer series
The Balmer series or Balmer lines in atomic physics, is the designation of one of a set of six different named series describing the spectral line emissions of the hydrogen atom....

.

The distance to Vega can be determined by measuring its parallax shift against the background stars as the Earth orbits the Sun. The first person to publish a star's parallax was Friedrich G. W. von Struve
Friedrich Georg Wilhelm von Struve
Friedrich Georg Wilhelm von Struve was a Danish-Baltic German astronomer from a famous dynasty.-Life:...

, when he announced a value of 0.125 arcseconds (0.125″) for Vega. But Friedrich Bessel
Friedrich Bessel
-References:* John Frederick William Herschel, A brief notice of the life, researches, and discoveries of Friedrich Wilhelm Bessel, London: Barclay, 1847 -External links:...

 was skeptical about Struve's data, and, when Bessel published a parallax of 0.314″ for the star system 61 Cygni
61 Cygni
61 Cygni,Not to be confused with 16 Cygni, a more distant system containing two G-type stars harboring the gas giant planet 16 Cygni Bb. sometimes called Bessel's Star or Piazzi's Flying Star, is a binary star system in the constellation Cygnus...

, Struve revised his value for Vega's parallax to nearly double the original estimate. This change cast further doubt on Struve's data. Thus most astronomers at the time, including Struve, credited Bessel with the first published parallax result. However, Struve's initial result was actually surprisingly close to the currently accepted value of 0.129″.

The brightness of a star, as seen from Earth, is measured with a standardized, logarithmic scale
Logarithmic scale
A logarithmic scale is a scale of measurement using the logarithm of a physical quantity instead of the quantity itself.A simple example is a chart whose vertical axis increments are labeled 1, 10, 100, 1000, instead of 1, 2, 3, 4...

. This apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 is a numerical value that decreases in value with increasing brightness of the star. The faintest stars visible to the unaided eye are sixth magnitude, while the brightest, Sirius, is of magnitude −1.47. To standardize the magnitude scale, astronomers chose Vega to represent magnitude zero at all wavelengths. Thus, for many years, Vega was used as a baseline for the calibration of absolute photometric
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...

 brightness scales. However, this is no longer the case, as the apparent magnitude zero point is now commonly defined in terms of a particular numerically specified flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...

. This approach is more convenient for astronomers, since Vega is not always available for calibration.

The UBV photometric system
UBV photometric system
UBV photometric system, also called the Johnson system , is a wide band photometric system for classifying stars according to their colors. It is the first known standardized photoelectric photometric system. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are...

 measures the magnitude of stars through ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

, blue, and yellow filters, producing U, B, and V values, respectively. Vega is one of six A0V stars that were used to set the initial mean values for this photometric system when it was introduced in the 1950s. The mean magnitudes for these six stars were defined as: = = 0. In effect, the magnitude scale has been calibrated so that the magnitude of these stars is the same in the yellow, blue, and ultraviolet parts of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....

. Thus, Vega 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
Jansky
The flux unit or jansky is a non-SI unit of spectral flux density equivalent to 10−26 watts per square metre per hertz...

. However, the flux density of Vega drops rapidly in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

, and is near 100 Jy at 5 micrometers
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

.

Photometric measurements of Vega during the 1930s appeared to show that the star had a low-magnitude variability on the order of ±0.03 magnitudes. This range of variability was near the limits of observational capability for that time, and so the subject of Vega's variability has been controversial. The magnitude of Vega was measured again in 1981 at the David Dunlap Observatory
David Dunlap Observatory
The David Dunlap Observatory is a large astronomical observatory site once owned by the University of Toronto, located just north of the city in Richmond Hill, Ontario within a estate. Its primary instrument is a 74-inch reflector telescope, at one time the second largest telescope in the world,...

 and showed some slight variability. Thus it was suggested that Vega showed occasional low-amplitude pulsations associated with a Delta Scuti variable
Delta Scuti variable
A Delta Scuti variable is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface. Typical brightness fluctuations are from 0.003 to 0.9 magnitudes in V over a period of a few hours, although the amplitude and period of the...

. This is a category of stars that oscillate in a coherent manner, resulting in periodic pulsations in the star's luminosity. Although Vega fits the physical profile for this type of variable, other observers have found no such variation. Thus the variability may be the result of systematic errors in measurement.

Vega became the first solitary main-sequence star beyond the Sun known to be an X-ray emitter when in 1979 it was observed from an imaging X-ray telescope launched on an Aerobee 350 from the White Sands Missile Range
White Sands Missile Range
White Sands Missile Range is a rocket range of almost in parts of five counties in southern New Mexico. The largest military installation in the United States, WSMR includes the and the WSMR Otera Mesa bombing range...

. In 1983, Vega became the first star found to have a disk of dust. The Infrared Astronomical Satellite (IRAS) discovered an excess of infrared radiation coming from the star, and this was attributed to energy emitted by the orbiting dust as it was heated by the star.

Visibility

Vega can often be seen near the zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...

 in the mid-northern latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s during the evening in the Northern Hemisphere summer. From mid-southern latitudes, it can be seen low above the northern horizon during the Southern Hemisphere winter. With a declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

 of +38.78°, Vega can only be viewed at latitudes north of 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 +51° N, Vega remains continually above the horizon as a circumpolar star
Circumpolar star
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets , due to its proximity to one of the celestial poles...

. Around July 1, Vega reaches midnight culmination
Culmination
In astronomy, the culmination of a planet, star, constellation, etc. is the altitude reached when the object transits over an observer's meridian....

 when it crosses the meridian
Meridian (astronomy)
This article is about the astronomical concept. For other uses of the word, see Meridian.In the sky, a meridian is an imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the...

 at that time.

This star lies at a vertex
Vertex (geometry)
In geometry, a vertex is a special kind of point that describes the corners or intersections of geometric shapes.-Of an angle:...

 of a widely spaced asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...

 called the Summer Triangle
Summer Triangle
The Summer Triangle is an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere's celestial sphere, with its defining vertices at Altair, Deneb, and Vega, being the brightest stars in the three constellations of Aquila, Cygnus, and Lyra.The English term was...

, which consists of the zero-magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 stars Vega in the constellation Lyra and Altair in Aquila
Aquila (constellation)
Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....

, plus the first magnitude star Deneb
Deneb
Deneb is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars...

 in Cygnus
Cygnus (constellation)
Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...

. This formation is the approximate shape of a right triangle
Right triangle
A right triangle or right-angled triangle is a triangle in which one angle is a right angle . The relation between the sides and angles of a right triangle is the basis for trigonometry.-Terminology:The side opposite the right angle is called the hypotenuse...

, with Vega located at its right angle
Right angle
In geometry and trigonometry, a right angle is an angle that bisects the angle formed by two halves of a straight line. More precisely, if a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles...

. The Summer Triangle is recognizable in the northern skies for there are few other bright stars in its vicinity.

The Lyrids
Lyrids
The Lyrids are a strong meteor shower lasting from April 16 to April 26 each year. The radiant of the meteor shower is located in the constellation Lyra, peaking at April 22—hence they are also called the Alpha Lyrids or April Lyrids. The source of the meteor shower is the periodic Comet...

 is a strong meteor shower
Meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...

 that peaks each year during April 21–22. When a small meteor enters the Earth's atmosphere at a high velocity, it produces a streak of light as the object is vaporized. During a shower, a multitude of meteors arrive from the same direction, and, from the perspective of an observer, their glowing trails appear to radiate from a single point in space. In the case of the Lyrids, the meteor trails radiate from the direction of Lyra, and hence are sometimes called the Alpha Lyrids. However, they actually originated from debris emitted by the comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

 C/1861 G1 Thatcher and have nothing to do with the star.

Physical properties

Vega's spectral class
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 is A0V, making it a blue-tinged white main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...

 star that is fusing
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 to helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 in its core. Since more massive stars use their fusion fuel more quickly than smaller ones, Vega's main sequence lifetime is only one billion years, a tenth of our Sun's. The current age of this star is about 455 million years, or up to about half its expected total main sequence life span. After leaving the main sequence, Vega will become a class-M red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...

 and shed much of its mass, finally becoming a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...

. At present, Vega has more than twice the mass of the Sun and its full luminosity is about 37 times the Sun's value. However, because of its high rate of rotation, the pole is considerably brighter than the equator. Since we see it nearly pole-on, its apparent luminosity from Earth is notably higher, about 57 times the Sun's value. If Vega is variable, then it may be a Delta Scuti type
Delta Scuti variable
A Delta Scuti variable is a variable star which exhibits variations in its luminosity due to both radial and non-radial pulsations of the star's surface. Typical brightness fluctuations are from 0.003 to 0.9 magnitudes in V over a period of a few hours, although the amplitude and period of the...

 with a period of about 0.107 days.

Most of the energy produced at Vega's core is generated by the carbon–nitrogen–oxygen cycle (CNO cycle
CNO cycle
The CNO cycle is one of two sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain. Unlike the proton–proton chain reaction, the CNO cycle is a catalytic cycle. Theoretical models show that the CNO cycle is the dominant source of energy in stars...

), a nuclear fusion
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...

 process that combines proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s to form helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 nuclei through intermediary nuclei of carbon, nitrogen, and oxygen. This process requires a temperature of about 15 million K, which is higher than the core temperature of the Sun, but is more efficient than the Sun's proton-proton chain reaction
Proton-proton chain reaction
The proton–proton chain reaction is one of several fusion reactions by which stars convert hydrogen to helium, the primary alternative being the CNO cycle. The proton–proton chain dominates in stars the size of the Sun or smaller....

 fusion reaction. The CNO cycle is highly temperature sensitive, which results in a convection zone
Convection zone
The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation...

 about the core that evenly distributes the 'ash' from the fusion reaction within the core region. The overlying atmosphere is in radiative equilibrium
Radiative transfer
Radiative transfer is the physical phenomenon of energy transfer in the form of electromagnetic radiation. The propagation of radiation through a medium is affected by absorption, emission and scattering processes. The equation of radiative transfer describes these interactions mathematically...

. This is in contrast to the Sun, which has a radiation zone
Radiation zone
The radiation zone is the middle zone in the Sun's interior. Energy travels out of the core into the radiation zone. Energy that travels through the radiation zone is in the form of electromagnetic radiation. The radiation zone is so dense that the waves bounce around...

 centered on the core with an overlying convection zone.

The energy flux from Vega has been precisely measured against standard light sources. At 5480 Å, the flux is 3,650 Jy
Jansky
The flux unit or jansky is a non-SI unit of spectral flux density equivalent to 10−26 watts per square metre per hertz...

 with an error margin of 2%. The visual spectrum of Vega is dominated by absorption lines of hydrogen; specifically by the hydrogen Balmer series
Balmer series
The Balmer series or Balmer lines in atomic physics, is the designation of one of a set of six different named series describing the spectral line emissions of the hydrogen atom....

 with the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

 at the n=2 principal quantum number
Principal quantum number
In atomic physics, the principal quantum symbolized as n is the firstof a set of quantum numbers of an atomic orbital. The principal quantum number can only have positive integer values...

. The lines of other elements are relatively weak, with the strongest being ionized magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, and chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

. The X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 emission from Vega is very low, demonstrating that the corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...

 for this star must be very weak or non-existent. However, as the pole of Vega is facing us and a polar coronal hole may be present, confirmation of a corona as the likely source of the X-rays detected from Vega (or the region very close to Vega) may be difficult as most of any coronal X-rays would not be emitted along the line of sight.

Using spectropolarimetry, a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 has been detected on the surface of Vega by a team of astronomers at the Observatoire du Pic du Midi
Pic du Midi de Bigorre
The Pic du Midi de Bigorre or simply Pic du Midi is a mountain in the French Pyrenees famous for its astronomical observatory, the Observatoire du Pic du Midi de Bigorre , part of the Observatoire Midi-Pyrénées .-Pic du Midi Observatory:Construction of the observatory began in 1878 under the...

. This is the first such detection of a magnetic field on a spectral class A star that is not an Ap
Ap and Bp star
Ap and Bp stars are peculiar stars of types A and B which show overabundances of some metals, such as strontium, chromium and europium; in addition, larger overabundances are often seen in praseodymium and neodymium...

 chemically peculiar star
Peculiar star
In astrophysics, peculiar stars have distinctly unusual metal abundances, at least in their surface layers.Chemically peculiar stars are common among hot main sequence stars...

. The average line of sight component of this field has a strength of . This is comparable to the mean magnetic field on the Sun. Magnetic fields of roughly 30 gauss have been reported for Vega, compared to about 1 gauss for the Sun.

Rotation

When the radius of Vega was measured to high accuracy with an interferometer
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....

, it resulted in an unexpectedly large estimated value of times the radius of the Sun. This is 60% larger than the radius of the star Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

, 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
CHARA array
The CHARA Array is an optical astronomical interferometer operated by The Center for High Angular Resolution Astronomy of the Georgia State University . CHARA is the World's highest angular resolution telescope at near-infrared wavelengths...

 in 2005–06 confirmed this deduction.

The pole of Vega—its axis of rotation—is inclined no more than five degrees from the line-of-sight to the Earth. The equator of Vega has a rotation
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....

 velocity of 274 km/s (for a rotation period of about 12.5 hours), which is 93% of the speed that would cause the star to start breaking up from centrifugal effects. This rapid rotation of Vega produces a pronounced equatorial bulge, so the radius of the equator is 23% larger than the polar radius. (The estimated polar radius of this star is solar radii, while the equatorial radius is solar radii.) From the Earth, this bulge is being viewed from the direction of its pole, producing the overly large radius estimate.

The local gravitational acceleration at the poles is greater than at the equator, so, by the Von Zeipel theorem, the local luminosity is also higher at the poles. This is seen as a variation in effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...

 over the star: the polar temperature is near 10,000 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

, while the equatorial temperature is 7,600 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

. As a result, if Vega were viewed along the plane of its equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, then the luminosity would be about half the apparent luminosity as viewed from the pole. This large temperature difference between the poles and the equator produces a strong 'gravity darkening
Gravity darkening
Gravity darkening, also referred to as Gravity Brightening, is an astronomical phenomenon where a star rotates so rapidly that it has a detectably oblate spheroid shape, such as in Regulus in the Leo constellation....

' effect. As viewed from the poles, this results in a darker (lower intensity) limb than would normally be expected for a spherically symmetric star. The temperature gradient may also mean Vega has a convection zone
Convection zone
The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation...

 around the equator, while the remainder of the atmosphere is likely to be in almost pure radiative equilibrium
Radiation zone
The radiation zone is the middle zone in the Sun's interior. Energy travels out of the core into the radiation zone. Energy that travels through the radiation zone is in the form of electromagnetic radiation. The radiation zone is so dense that the waves bounce around...

.

If Vega was actually a slowly rotating, spherically symmetric star and it was radiating the same energy as viewed from the Earth, then the luminosity of Vega would be 57 times the luminosity of the Sun. This value is much larger than the luminosity of a typical slowly rotating star with the same mass as Vega. Thus the discovery of fast rotation of Vega resolved this discrepancy. The true full luminosity of Vega is about 37 times the luminosity of the Sun.

As Vega had long been used as a standard star for calibrating telescopes, the discovery that it is rapidly rotating may challenge some of the underlying assumptions that were based on it being spherically symmetric. With the viewing angle and rotation rate of Vega now better known, this will allow for improved instrument calibrations.

Element abundance

Astronomers term "metals" those elements with higher atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

s than helium. The metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...

 of Vega's photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

 is only about 32% of the abundance of heavy elements in the Sun's atmosphere. (Compare this, for example, to a three-fold metallicity abundance in the similar star Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

 as compared to the Sun.) For comparison, the Sun has an abundance of elements heavier than helium of about ZSol = 0.0172 ± 0.002. Thus, in terms of abundances, only about 0.54% of Vega consists of elements heavier than helium.

The unusually low metallicity of Vega makes it a weak Lambda Boötis
Lambda Boötis
Lambda Boötis is a star in the constellation Boötes.Lambda Boötis is a white A-type main sequence dwarf with an apparent magnitude of +4.18. It is approximately 97.1 light-years from Earth. Lambda Boötis is the prototype of a group of rare stars known as Lambda Boötis stars, all of which are...

-type star. However, the reason for the existence of such chemically peculiar, spectral class
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 A0-F0 stars remains unclear. One possibility is that the chemical peculiarity may be the result of diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 or mass loss, although stellar models show that this would normally only occur near the end of a star's hydrogen-burning lifespan. Another possibility is that the star formed from an interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

 of gas and dust that was unusually metal-poor.

The observed helium to hydrogen ratio in Vega is 0.030 ± 0.005, which is about 40% lower than the Sun. This may be caused by the disappearance of a helium convection zone
Convection zone
The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation...

 near the surface. Energy transfer is instead performed by the radiative process
Radiation zone
The radiation zone is the middle zone in the Sun's interior. Energy travels out of the core into the radiation zone. Energy that travels through the radiation zone is in the form of electromagnetic radiation. The radiation zone is so dense that the waves bounce around...

, which may be causing an abundance anomaly through diffusion.

Kinematics

The radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...

 of Vega is the component of this star's motion along the line-of-sight to the Earth. Movement away from the Earth will cause the light from Vega to shift to a lower frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 (toward the red), or to a higher frequency (toward the blue) if the motion is toward the Earth. Thus the velocity can be measured from the amount of redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...

 (or blueshift) of the star's spectrum. Precise measurements of this redshift give a value of . The minus sign indicates a relative motion toward the Earth.

Motion transverse to the line of sight causes the position of Vega to shift with respect to the more distant background stars. Careful measurement of the star's position allows this angular movement, known as proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...

, to be calculated. Vega's proper motion is (mas) per year in right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

—the celestial equivalent of longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

—and in declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

, which is equivalent to a change in latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

. The net proper motion of Vega is 327.78 mas/y, which results in angular movement of a degree every 11,000 years.

In the Galactic coordinate system
Galactic coordinate system
The galactic coordinate system is a celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy. The "equator" is aligned to the galactic plane...

, the space velocity components of Vega are (U, V, W) = , for a net space velocity of 19 km/s. The radial component of this velocity—in the direction of the Sun—is −13.9 km/s, while the transverse velocity is 9.9 km/s. Although Vega is at present only the fifth-brightest star in the sky, the star is slowly brightening as proper motion causes it to approach the Sun. Vega will eventually become the brightest star in the sky in around 210,000 years, will attain a peak brightness of magnitude –0.81 in about 290,000 years and will be the brightest star in the sky for about 270,000 years.

Based on this star's kinematic properties, it appears to belong to a stellar association called the Castor Moving Group
Castor Moving Group
The Castor Moving Group is a moving group, that is, a set of stars with common velocities in space, thought to have a common origin. The stars that have been identified as part of the group include Castor, Fomalhaut, Vega, α Cephei and α Librae. They are all of similar age.-Discovery and...

. However, Vega may be much older than this group, so the membership remains uncertain. This group contains about 16 stars, including Alpha Librae
Alpha Librae
Alpha Librae is the second brightest star in the constellation Libra . It has the traditional name Zubenelgenubi. The name, from Arabic الزبن الجنوبي , means "southern claw" and was coined before Libra was recognized as distinct from Scorpius...

, Alpha Cephei
Alpha Cephei
Alpha Cephei is a second magnitude star in the constellation of Cepheus that is relatively close to Earth at only 49 light years...

, Castor
Castor (star)
Castor is the second brightest star in the constellation Gemini and one of the brightest stars in the night sky. Although it has the Bayer designation "alpha", it is actually fainter than Beta Geminorum...

, Fomalhaut
Fomalhaut
Fomalhaut is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. Fomalhaut can be seen low in the southern sky in the northern hemisphere in fall and early winter evenings. Near latitude 50˚N, it sets around the time Sirius rises, and does not...

 and Vega. All members of the group are moving in nearly the same direction with similar space velocities. Membership in a moving group implies a common origin for these stars in an open cluster
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...

 that has since become gravitationally unbound. The estimated age of this moving group is , and they have an average space velocity of 16.5 km/s.

Infrared excess

One of the early results from the Infrared Astronomy Satellite (IRAS) was the discovery of excess infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 flux coming from Vega, beyond what would be expected from the star alone. This excess was measured at wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

s of 25, 60, and 100 μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

, and came from within an angular radius of 10 arcseconds (10″) centered on the star. At the measured distance of Vega, this corresponded to an actual radius of 80 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

s (AU), where an AU is the average radius of the Earth's orbit around the Sun. It was proposed that this radiation came from a field of orbiting particles with a dimension on the order of a millimeter, as anything smaller would eventually be removed from the system by radiation pressure or drawn into the star by means of Poynting-Robertson drag. The latter is the result of radiation pressure creating an effective force that opposes the orbital motion of a dust particle, causing it to spiral inward. This effect is most pronounced for tiny particles that are closer to the star.

Subsequent measurements of Vega at 193 μm showed a lower than expected flux for the hypothesized particles, suggesting that they must instead be on the order of 100 μm or less. To maintain this amount of dust in orbit around Vega, a continual source of replenishment would be required. A proposed mechanism for maintaining the dust was a disk of coalesced bodies that were in the process of collapsing to form a planet. Models fitted to the dust distribution around Vega indicate that it is a 120 AU-radius circular disk viewed from nearly pole-on. In addition, there is a hole in the center of the disk with a radius of no less than 80 AU.

Following the discovery of an infrared excess around Vega, other stars have been found that display a similar anomaly that is attributable to dust emission. As of 2002, about 400 of these stars have been found, and they have come to be termed "Vega-like" or "Vega-excess" stars. It is believed that these may provide clues to the origin of the Solar System.

Debris disk

By 2005, the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...

 had produced high resolution infrared images of the dust around Vega. It was shown to extend out to 43″ (330 AU) at a wavelength of 24 μm, 70″ (543 AU) at 70 μm and 105″ (815 AU) at 160 μm. These much wider disks were found to be circular and free of clumps, with dust particles ranging from 1–50 μm in size. The estimated total mass of this dust is 3 times the mass of the Earth. Production of the dust would require collisions between asteroids in a population corresponding to the Kuiper Belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...

 around the Sun. Thus the dust is more likely created by a debris disk
Debris disk
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a...

 around Vega, rather than from a protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...

 as was earlier thought.

The inner boundary of the debris disk was estimated at 11″ ± 2″, or 70–102 AU. The disk of dust is produced as radiation pressure from Vega pushes debris from collisions of larger objects outward. However, continuous production of the amount of dust observed over the course of Vega's lifetime would require an enormous starting mass—estimated as hundreds of times the mass of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

. Hence it is more likely to have been produced as the result of a relatively recent breakup of a moderate-sized (or larger) comet or asteroid, which then further fragmented as the result of collisions between the smaller components and other bodies. This dusty disk would be relatively young on the time scale of the star's age, and it will eventually be removed unless other collision events supply more dust.

Observations, first with the Palomar Testbed Interferometer
Palomar Testbed Interferometer
The Palomar Testbed Interferometer was a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was built by Caltech/JPL and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer...

 in 2001 and then later confirmed with the CHARA array
CHARA array
The CHARA Array is an optical astronomical interferometer operated by The Center for High Angular Resolution Astronomy of the Georgia State University . CHARA is the World's highest angular resolution telescope at near-infrared wavelengths...

 at Mt. Wilson in 2006, revealed evidence for an inner dust band around Vega. Originating within 8 AU of the star, this exozodiacal dust
Exozodiacal dust
Exozodiacal dust is the exoplanetary analog of zodiacal dust, the 1-100 micrometre-sized grains of silicate dust that fill the plane of the solar system, especially interior to the asteroid belt. As for the zodiacal dust, these grains are probably produced by outgasing comets as well as by...

 may be evidence of dynamical perturbations within the system. This may be caused by an intense bombardment of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

s or meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

s, and may be evidence for the existence of a planetary system.

Possible planets

Observations from the James Clerk Maxwell Telescope
James Clerk Maxwell Telescope
The James Clerk Maxwell Telescope is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum...

 in 1997 revealed an "elongated bright central region" that peaked at 9″ (70 AU) to the northeast of Vega. This was hypothesized as either a perturbation of the dust disk by a planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...

 or else an orbiting object that was surrounded by dust. However, images by the Keck telescope had ruled out a companion down to magnitude 16, which would correspond to a body with more than 12 times the mass of Jupiter. Astronomers at the Joint Astronomy Centre
Joint Astronomy Centre
The Joint Astronomy Centre operates British, Canadian and Dutch telescopes at Mauna Kea Observatory, and provides support for other telescopes and public outreach activities...

 in Hawaii and at UCLA suggested that the image may indicate a planetary system still undergoing formation.

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. Dust would collect in orbits that have mean-motion resonances
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...

 with this planet—where their orbital periods form integer fractions with the period of the planet—producing the resulting clumpiness.

In 2003 it was hypothesized that these lumps could be caused by a roughly Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

-mass planet having migrated
Planetary migration
Planetary migration occurs when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite's orbital parameters, especially its semi-major axis...

 from 40 to 65 AU over 56 million years, an orbit large enough to allow the formation of smaller rocky planets closer to Vega. The migration of this planet would likely require gravitational interaction with a second, higher mass planet in a smaller orbit.

Using a coronagraph
Coronagraph
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved...

 on the Subaru telescope
Subaru (telescope)
Subaru Telescope is the 8.2 metre flagship telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades...

 in Hawaii in 2005, astronomers were able to further constrain the size of a planet orbiting Vega to no more than 5–10 times the mass of Jupiter. The issue of possible clumps in the debris disc was revisited in 2007 using newer, more sensitive instrumentation on the Plateau de Bure Interferometer
Plateau de Bure Interferometer
The Plateau de Bure Interferometer is a six-antenna interferometer on the Plateau de Bure in the French Alps, operated by the Institut de radioastronomie millimétrique....

. The observations showed that the debris ring is smooth and symmetric. No evidence was found of the blobs reported earlier, casting doubts on the hypothesized giant planet.

Although a planet has yet to be directly observed around Vega, the presence of a planetary system can not yet be precluded. Thus there could be smaller, terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...

s orbiting closer to the star. The inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...

 of planetary orbits around Vega is likely to be closely aligned to the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

ial plane of this star. From the perspective of an observer on a hypothetical planet around Vega, the Sun would appear as a faint 4.3 magnitude star in the Columba
Columba (constellation)
Columba is a small, faint constellation created in the late sixteenth century. Its name is Latin for dove. It is located just south of Canis Major and Lepus.-History:...

 constellation.

Etymology and cultural significance

The name Wega (later Vega) comes from a loose transliteration of the Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 word meaning "falling" or "landing", via the phrase "the alighting vulture". The term "Al Nesr al Waki" appeared in the Al Achsasi Al Mouakket star catalogue and was translated into Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 as "Vulture Cadens". The constellation was represented as a vulture in ancient Egypt
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

, and as an eagle or vulture in ancient India
History of India
The history of India begins with evidence of human activity of Homo sapiens as long as 75,000 years ago, or with earlier hominids including Homo erectus from about 500,000 years ago. The Indus Valley Civilization, which spread and flourished in the northwestern part of the Indian subcontinent from...

. The Arabic name then appeared in the western world
Western world
The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

 in the Alfonsine Tables
Alfonsine tables
The Alfonsine tables provided data for computing the position of the Sun, Moon and planets relative to the fixed stars....

, which were drawn up between 1215 and 1270 by order of Alfonso X.

Each night the positions of the stars appear to change as the Earth rotates. However, when a star is located along the Earth's axis of rotation, it will remain in the same position and thus is called a pole star
Pole star
The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

. The direction of the Earth's axis of rotation gradually changes over time in a process known as the precession of the equinoxes. A complete precession cycle requires 25,770 years, during which time the pole of the Earth's rotation follows a circular path across the celestial sphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

 that passes near several prominent stars. At present the pole star is Polaris
Polaris
Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

, but around 12,000 BC the pole was pointed only five degrees away from Vega. Through precession, the pole will again pass near Vega around AD 14,000. It is the brightest of the successive northern pole stars.

Among the northern Polynesia
Polynesia
Polynesia is a subregion of Oceania, made up of over 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are termed Polynesians and they share many similar traits including language, culture and beliefs...

n people, Vega was known as whetu o te tau, the year star. For a period of history it marked the start of their new year when the ground would be prepared for planting. Eventually this function became denoted by the Pleiades
Pleiades (star cluster)
In astronomy, the Pleiades, or Seven Sisters , is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky...

.

The Assyrians
Assyrian people
The Assyrian people are a distinct ethnic group whose origins lie in ancient Mesopotamia...

 named this pole star Dayan-same, the "Judge of Heaven", while in Akkadian
Akkadian language
Akkadian is an extinct Semitic language that was spoken in ancient Mesopotamia. The earliest attested Semitic language, it used the cuneiform writing system derived ultimately from ancient Sumerian, an unrelated language isolate...

 it was Tir-anna, "Life of Heaven". In Babylon
Babylon
Babylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...

ian astronomy, Vega may have been one of the stars named Dilgan, "the Messenger of Light". To the ancient Greeks
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

, the constellation Lyra was formed from the harp of Orpheus
Orpheus
Orpheus was a legendary musician, poet, and prophet in ancient Greek religion and myth. The major stories about him are centered on his ability to charm all living things and even stones with his music; his attempt to retrieve his wife from the underworld; and his death at the hands of those who...

, with Vega as its handle. For the Roman Empire
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

, the start of autumn was based upon the hour at which Vega set below the horizon.

In Chinese mythology
Chinese mythology
Chinese mythology is a collection of cultural history, folktales, and religions that have been passed down in oral or written tradition. These include creation myths and legends and myths concerning the founding of Chinese culture and the Chinese state...

, there is a love story of Qi Xi
Qi Xi
Qixi Festival , also known as Magpie Festival, falls on the seventh day of the seventh lunar month on the Chinese calendar; thus its name. It inspired Tanabata in Japan, Chilseok in Korea, and Thất Tịch in Vietnam...

  in which Niu Lang and his two children (β and γ Aquilae) are separated from their mother Zhi Nü who is on the far side of the river, the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. However, one day per year on the seventh day of the seventh month of the Chinese lunisolar calendar, magpies make a bridge so that Niu Lang and Zhi Nü can be together again for a brief encounter. The Japanese Tanabata
Tanabata
is a Japanese star festival, originating from the Chinese Qixi Festival. It celebrates the meeting of the deities Orihime and Hikoboshi . According to legend, the Milky Way separates these lovers, and they are allowed to meet only once a year on the seventh day of the seventh lunar month of the...

 festival, in which Vega is known as orihime (織姫), is also based on this legend.

Vega is mentioned in a Chinese legend about Zhang Qian
Zhang Qian
Zhang Qian was an imperial envoy to the world outside of China in the 2nd century BCE, during the time of the Han Dynasty...

, though some argue that the historical person is not the subject of the legend; he just shared a name. It was said that he was commissioned to find the source of the Yellow River
Yellow River
The Yellow River or Huang He, formerly known as the Hwang Ho, is the second-longest river in China and the sixth-longest in the world at the estimated length of . Originating in the Bayan Har Mountains in Qinghai Province in western China, it flows through nine provinces of China and empties into...

, which was believed to flow from heaven as a continuation of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. After sailing up-river for many days, he saw a girl spinning and a cow herd. Upon asking the girl where he was, she presented him with her shuttle
Shuttle (weaving)
A shuttle is a tool designed to neatly and compactly store weft yarn while weaving. Shuttles are thrown or passed back and forth through the shed, between the yarn threads of the warp in order to weave in the weft....

 with instructions to show it to the astrologer Yen Chün-p'ing. When he returned, the astrologer recognised it as the shuttle of the Weaving Girl (Vega), and, moreover, said that at the time Zhang received the shuttle, he had seen a wandering star interpose itself between the Weaving Girl and the cow herd.

In Zoroastrianism
Zoroastrianism
Zoroastrianism is a religion and philosophy based on the teachings of prophet Zoroaster and was formerly among the world's largest religions. It was probably founded some time before the 6th century BCE in Greater Iran.In Zoroastrianism, the Creator Ahura Mazda is all good, and no evil...

, Vega was sometimes associated with Vanant, a minor divinity whose name means "conqueror".

In Hindu mythology, Vega is called Abhijit. The author of Mahabharat, Maharshi Vyas, mentions in the chapter Vana Parva (Chap. 230, Verses 8–11): "Contesting against Abhijit (Vega), the constellation Krittika (Pleiades
Pleiades (star cluster)
In astronomy, the Pleiades, or Seven Sisters , is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky...

) went to "Vana" the Summer Solstice
Solstice
A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

 to heat the summer. Then the star Abhijit slipped down in the sky." P. V. Vartak suggests in his book, The Scholarly Dating of Mahabharat, that the "slipping of Abhijit" and ascension of Krittika (Pleiades) might refer to the gradual drop of Vega as a pole star since 12,000 BC.

Medieval astrologers counted Vega as one of the Behenian stars and related it to chrysolite
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

 and winter savory
Winter savory
Winter savory is a perennial herb in the family Lamiaceae, native to warm temperate regions of southern Europe.It is a semi-evergreen, semi-woody subshrub growing to over tall. The leaves are opposite, oval-lanceolate, 1–2 cm long and 5 mm broad...

. Cornelius Agrippa listed its kabbalistic sign under Vultur cadens, a literal Latin translation of the Arabic name. Medieval star charts also listed the alternate names Waghi, Vagieh and Veka for this star.

Vega became the first star to have a car named after it when Chevrolet
Chevrolet
Chevrolet , also known as Chevy , is a brand of vehicle produced by General Motors Company . Founded by Louis Chevrolet and ousted GM founder William C. Durant on November 3, 1911, General Motors acquired Chevrolet in 1918...

 launched the Vega
Chevrolet Vega
The Chevrolet Vega is a subcompact, two-door automobile that was produced by the Chevrolet division of General Motors for the 1971-1977 model years. Named after the star Vega, the car was powered by a lightweight aluminum-block inline four-cylinder engine...

 in 1971. Other vehicles named after Vega include the ESA's
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

 Vega
Vega (launcher)
Vega is an expendable launch system being developed for Arianespace jointly by the Italian Space Agency and the European Space Agency. Development began in 1998 and the first launch, which will take place from the Guiana Space Centre, is planned for early 2012...

 launch system and the Lockheed Vega
Lockheed Vega
|-See also:-References:NotesCitationsBibliography* Allen, Richard Sanders. Revolution in the Sky: Those Fabulous Lockheeds, The Pilots Who Flew Them. Brattleboro, Vermont: The Stephen Greene Press, 1964....

 aircraft. Vega is the title of a song by the Penguin Cafe Orchestra
Penguin Cafe Orchestra
The Penguin Cafe Orchestra was a collective of performing musicians created by classically trained British guitarist, composer and arranger Simon Jeffes...

on their album Concert Program.

External links

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