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Vega is the brightest
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
in the
northern Northern may refer to the following: Geography * North, a point in direction * Northern Europe, the northern part or region of Europe * Northern Highland, a region of Wisconsin, United States * Northern Province, Sri Lanka * Northern Range, a ra ...
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...
of Lyra. It has the
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...
α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, and one of the most luminous stars in the Sun's neighborhood. It is the fifth-brightest star in the night sky, and the second-brightest star in the northern celestial hemisphere, after Arcturus. 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 Northern may refer to the following: Geography * North, a point in direction * Northern Europe, the northern part or region of Europe * Northern Highland, a region of Wisconsin, United States * Northern Province, Sri Lanka * Northern Range, a ra ...
pole star around 12,000 BCE and will be so again around the year 13,727, when its declination will be . Vega was the first star other than the Sun to have its image and spectrum photographed. It was one of the first stars whose distance was estimated through
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. Due to foreshortening, nearby objects ...
measurements. Vega has functioned as the baseline for calibrating the photometric brightness scale and was one of the stars used to define the zero point for the UBV photometric system. 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. Compared with the Sun, Vega has a lower abundance of elements heavier than helium. Vega is also a variable star that varies slightly in brightness. It is rotating rapidly with a velocity of at the equator. This causes the equator to bulge outward due to
centrifugal Centrifugal (a key concept in rotating systems) may refer to: *Centrifugal casting (industrial), Centrifugal casting (silversmithing), and Spin casting (centrifugal rubber mold casting), forms of centrifigual casting *Centrifugal clutch *Centrifug ...
effects, and, as a result, there is a variation of temperature across the star's
photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
that reaches a maximum at the poles. From Earth, Vega is observed from the direction of one of these poles. Based on an observed excess emission of infrared 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, which is analogous to the
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
in the Solar System. Stars that display an infrared excess due to dust emission are termed Vega-like stars. In 2021, a candidate
ultra-hot Neptune A hot Neptune or Hoptune is a type of giant planet with a mass similar to that of Uranus or Neptune orbiting close to its star, normally within less than 1 AU. The first hot Neptune to be discovered with certainty was Gliese 436 b in 2007, an exo ...
on a 2.43-day orbit around Vega was discovered with the
radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
method, additionally, another possible Saturn-mass signal with a period of about 200 days.


Nomenclature

'' α Lyrae'' ( Latinised to ''Alpha Lyrae'') is the star's
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...
. The traditional name ''Vega'' (earlier ''Wega'') comes from a loose transliteration of the Arabic word ' ( Arabic: واقع) meaning "falling" or "landing", via the phrase ' ( Arabic: النّسر الْواقع), "the falling eagle". In 2016, the International Astronomical Union (IAU) organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 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 Catalog of Star Names.


Observation

Vega can often be seen near the zenith in the mid-northern latitudes during the evening in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
summer. From mid-southern latitudes, it can be seen low above the northern horizon during the Southern Hemisphere winter. With a
declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...
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 continuously above the horizon as a circumpolar star. Around July 1, Vega reaches midnight
culmination In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events were also known as meridian transits ...
when it crosses the
meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...
at that time. 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. 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 In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...
that passes near several prominent stars. At present the pole star is
Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...
, but around 12,000 BCE the pole was pointed only five degrees away from Vega. Through precession, the pole will again pass near Vega around 14,000 CE. Vega is the brightest of the successive northern pole stars. In 210,000 years, Vega will become the brightest star in the night sky, – based on computations from
HIPPARCOS ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...
data. (The calculations exclude stars whose distance or
proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
is uncertain.) tp://tlgleonid.asuscomm.com/HITACHI/BOOK_ASTRO/S&T/SkyandTelescope_1998%20-%20astronomy/04/199804059063.pdf PDF/ref> and will peak in brightness in 290,000 years with an apparent magnitude of –0.81. This star lies at a
vertex Vertex, vertices or vertexes may refer to: Science and technology Mathematics and computer science *Vertex (geometry), a point where two or more curves, lines, or edges meet *Vertex (computer graphics), a data structure that describes the position ...
of a widely spaced asterism called the
Summer Triangle The Summer Triangle is an astronomical asterism in the northern celestial hemisphere. The defining vertices of this imaginary triangle are at Altair, Deneb, and Vega, each of which is the brightest star of its constellation ( Aquila, Cygnus, ...
, which consists of Vega plus the two first-magnitude stars Altair, in Aquila, and Deneb in Cygnus. This formation is the approximate shape of a right triangle, with Vega located at its
right angle In geometry and trigonometry, a right angle is an angle of exactly 90 Degree (angle), degrees or radians corresponding to a quarter turn (geometry), turn. If a Line (mathematics)#Ray, ray is placed so that its endpoint is on a line and the ad ...
. The Summer Triangle is recognizable in the northern skies for there are few other bright stars in its vicinity.


Observational history

Astrophotography, the photography of celestial objects, began in 1840 when
John William Draper John William Draper (May 5, 1811 – January 4, 1882) was an English-born American scientist, philosopher, physician, chemist, historian and photographer. He is credited with producing the first clear photograph of a female face (1839–40) and ...
took an image of the Moon using the
daguerreotype Daguerreotype (; french: daguerréotype) was the first publicly available photographic process; it was widely used during the 1840s and 1850s. "Daguerreotype" also refers to an image created through this process. Invented by Louis Daguerre an ...
process. On 17 July 1850, Vega became the first star (other than the Sun) to be photographed, when it was imaged by William Bond and
John Adams Whipple John Adams Whipple (September 10, 1822 – April 10, 1891) 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 pho ...
at the Harvard College Observatory, also with a daguerreotype. In August 1872, Henry Draper took a photograph of Vega's spectrum, the first photograph of a star's spectrum showing absorption lines. Similar lines had already been identified in the spectrum of the Sun. 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. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. 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, when he announced a value of 0.125 arcsecond () for Vega. Friedrich Bessel was skeptical about Struve's data, and, when Bessel published a parallax of 0.314″ for the star system 61 Cygni, 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 close to the currently accepted value of 0.129″, as determined by the ''
Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...
''
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. His ...
satellite. The brightness of a star, as seen from Earth, is measured with a standardized,
logarithmic scale A logarithmic scale (or log scale) is a way of displaying numerical data over a very wide range of values in a compact way—typically the largest numbers in the data are hundreds or even thousands of times larger than the smallest numbers. Such a ...
. This apparent magnitude 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 in the night sky, Sirius, is of magnitude −1.46. 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 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 describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
. This approach is more convenient for astronomers, since Vega is not always available for calibration and varies in brightness. The UBV photometric system measures the magnitude of stars through ultraviolet, 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. Thus, Vega has a relatively flat electromagnetic spectrum in the visual region—wavelength range 350–850
nanometer 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
s, most of which can be seen with the human eye—so the flux densities are roughly equal; 2,000–. However, the flux density of Vega drops rapidly in the infrared, and is near at . Photometric measurements of Vega during the 1930s appeared to show that the star had a low-magnitude variability on the order of ±0.03 magnitude (around ±2.8% luminosity). 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 and showed some slight variability. Thus it was suggested that Vega showed occasional low-amplitude pulsations associated with a Delta Scuti variable. 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 was thought to possibly be the result of systematic errors in measurement. However, a 2007 article surveyed these and other results, and concluded that "A conservative analysis of the foregoing results suggests that Vega is quite likely variable in the 1–2% range, with possible occasional excursions to as much as 4% from the mean". Also, a 2011 article affirms that "The long-term (year-to-year) variability of Vega was confirmed". 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. 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.


Physical characteristics

Vega's spectral class is A0V, making it a blue-tinged white main-sequence star that is fusing hydrogen to helium in its core. Since more massive stars use their fusion fuel more quickly than smaller ones, Vega's main-sequence lifetime is roughly one billion years, a tenth of the Sun's. The current age of this star is about 455 million years, or up to about half its expected total main-sequence lifespan. After leaving the main sequence, Vega will become a class-M
red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...
and shed much of its mass, finally becoming a white dwarf. At present, Vega has more than twice the mass of the Sun and its bolometric luminosity is about 40 times the Sun's. Because it is rotating rapidly, approximately once every 12.5 hours, and seen nearly pole-on, its apparent luminosity, calculated assuming it was the same brightness all over, is about 57 times the Sun's. If Vega is variable, then it may be a Delta Scuti type with a period of about 0.107 day. Most of the energy produced at Vega's core is generated by the carbon–nitrogen–oxygen cycle ( CNO cycle), a nuclear fusion process that combines
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s to form helium nuclei through intermediary nuclei of carbon, nitrogen and oxygen. This process becomes dominant at a temperature of about 17 million K, which is slightly higher than the core temperature of the Sun, but is less efficient than the Sun's proton–proton chain fusion reaction. The CNO cycle is highly temperature sensitive, which results in a convection zone about the core that evenly distributes the 'ash' from the fusion reaction within the core region. The overlying atmosphere is in
radiative equilibrium Radiative equilibrium is the condition where the total thermal radiation leaving an object is equal to the total thermal radiation entering it. It is one of the several requirements for thermodynamic equilibrium, but it can occur in the absence of t ...
. This is in contrast to the Sun, which has a radiation zone centered on the core with an overlying convection zone. The energy flux from Vega has been precisely measured against standard light sources. At , the flux density is with an error margin of 2%. The visual spectrum of Vega is dominated by
absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
s of hydrogen; specifically by the hydrogen Balmer series with the electron at the n=2 principal quantum number. The lines of other elements are relatively weak, with the strongest being ionized magnesium, iron and
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
. The X-ray emission from Vega is very low, demonstrating that the corona for this star must be very weak or non-existent. However, as the pole of Vega is facing Earth 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 Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or hav ...
, a
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
has been detected on the surface of Vega by a team of astronomers at the
Observatoire du Pic du Midi The Pic du Midi de Bigorre or simply the Pic du Midi (elevation ) is a mountain in the France, French Pyrenees. It is the site of the Pic du Midi Observatory. Pic du Midi Observatory The Pic du Midi Observatory (french: Observatoire du Pic ...
. This is the first such detection of a magnetic field on a spectral class A star that is not an Ap chemically peculiar star. 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 G have been reported for Vega, compared to about 1 G for the Sun. In 2015, bright starspots were detected on the star's surface—the first such detection for a normal A-type star, and these features show evidence of rotational modulation with a period of 0.68 day.


Rotation

Vega has a rotation period of 12.5 hours, much faster than the Sun's rotational period but similar to, and slightly slower than, those of Jupiter and
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
. Because of that, Vega is significantly
oblate In Christianity (especially in the Roman Catholic, Orthodox, Anglican and Methodist traditions), an oblate is a person who is specifically dedicated to God or to God's service. Oblates are individuals, either laypersons or clergy, normally livi ...
like those two planets. When the radius of Vega was measured to high accuracy with an
interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...
, it resulted in an unexpectedly large estimated value of times the
radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\t ...
. 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. 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
rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
velocity for Vega is along the equator, much higher than the observed (i.e.
projected Projected is an American rock supergroup consisting of Sevendust members John Connolly and Vinnie Hornsby, Alter Bridge and Creed drummer Scott Phillips, and former Submersed and current Tremonti guitarist Eric Friedman. The band released thei ...
) 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 Centrifugal (a key concept in rotating systems) may refer to: *Centrifugal casting (industrial), Centrifugal casting (silversmithing), and Spin casting (centrifugal rubber mold casting), forms of centrifigual casting *Centrifugal clutch *Centrifug ...
effects. This rapid rotation of Vega produces a pronounced equatorial bulge, so the radius of the equator is 19% 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 surface gravity at the poles is greater than at the equator, which produces a variation in
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. Effective temperature is often used as an estimate of a body's surface temperature ...
over the star: the polar temperature is near , while the equatorial temperature is about . This large temperature difference between the poles and the equator produces a strong
gravity darkening Gravity darkening, also referred to as gravity brightening, is an astronomical phenomenon where the poles of a star are brighter than the equator, due to rapid rotation and oblate shape. When a star is oblate, it has a larger radius at its equat ...
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 that Vega has a convection zone around the equator, while the remainder of the atmosphere is likely to be in almost pure
radiative equilibrium Radiative equilibrium is the condition where the total thermal radiation leaving an object is equal to the total thermal radiation entering it. It is one of the several requirements for thermodynamic equilibrium, but it can occur in the absence of t ...
. By the
Von Zeipel theorem In astrophysics, the von Zeipel theorem states that the radiative flux F in a uniformly rotating star is proportional to the local effective gravity g_\text. The theorem is named after Swedish astronomer Edvard Hugo von Zeipel. The theorem is: : ...
, the local luminosity is higher at the poles. As a result, if Vega were viewed along the plane of its
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
instead of almost pole-on, then its overall brightness would be lower. 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 improved instrument calibrations.


Element abundance

In astronomy, those elements with higher atomic numbers than helium are termed "metals". The
metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...
of Vega's
photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
is only about 32% of the abundance of heavy elements in the Sun's atmosphere. (Compare this, for example, to a threefold metallicity abundance in the similar star Sirius as compared to the Sun.) For comparison, the Sun has an abundance of elements heavier than helium of about ZSol = . Thus, in terms of abundances, only about 0.54% of Vega consists of elements heavier than helium. Nitrogen is slightly ''more'' abundant, oxygen is only marginally less abundant and
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
abundance is about 50% of solar. On the other hand, Vega has only 10% to 30% of the solar abundance for most other major elements with
barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...
and scandium below 10%. The unusually low metallicity of Vega makes it a weak Lambda Boötis star. However, the reason for the existence of such chemically peculiar, spectral class A0–F0 stars remains unclear. One possibility is that the chemical peculiarity may be the result of diffusion 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 In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
of gas and dust that was unusually metal-poor. The observed helium to hydrogen ratio in Vega is , which is about 40% lower than the Sun. This may be caused by the disappearance of a helium convection zone near the surface. Energy transfer is instead performed by the radiative process, which may be causing an abundance anomaly through diffusion.


Kinematics

The
radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
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 (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 shift of the star's spectrum. Precise measurements of this blueshift 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 is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
, to be calculated. Vega's proper motion is (mas) per year in
right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...
—the celestial equivalent of longitude—and in
declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...
, which is equivalent to a change in latitude. The net proper motion of Vega is , which results in angular movement of a degree every . In the galactic coordinate system, the space velocity components of Vega are (U, V, W) = , for a net space velocity of . The radial component of this velocity—in the direction of the Sun—is , while the transverse velocity is . Although Vega is at present only the fifth-brightest star in the night sky, the star is slowly brightening as proper motion causes it to approach the Sun. Vega will make its closest approach in an estimated 264,000 years at a perihelion distance of . Based on this star's kinematic properties, it appears to belong to a stellar association called the
Castor Moving Group The Castor Moving Group, or Castor stream, is a moving group of stars sharing similar velocities and directions. The stars that have been identified as part of the group include Castor, Fomalhaut, Vega, α Cephei and α Librae. While the repor ...
. However, Vega may be much older than this group, so the membership remains uncertain. This group contains about 16 stars, including Alpha Librae,
Alpha Cephei Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin , is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (''ly''). ...
, Castor, Fomalhaut 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 that has since become gravitationally unbound. The estimated age of this moving group is , and they have an average space velocity of .


Possible planetary system


Infrared excess

One of the early results from the
Infrared Astronomy Satellite The Infrared Astronomical Satellite ( Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mo ...
(IRAS) was the discovery of excess infrared flux coming from Vega, beyond what would be expected from the star alone. This excess was measured at wavelengths of 25, 60 and , and came from within an angular radius of () centered on the star. At the measured distance of Vega, this corresponded to an actual radius of (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 millimetre, 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 showed a lower than expected flux for the hypothesized particles, suggesting that they must instead be on the order of 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-astronomical-unit-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 . 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 disks

By 2005, the
Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...
had produced high-resolution infrared images of the dust around Vega. It was shown to extend out to 43″ () at a wavelength of , 70″ () at and () at . These much wider disks were found to be circular and free of clumps, with dust particles ranging from 1– in size. The estimated total mass of this dust is 3 times the mass of the Earth (around 7.5 times more massive than the asteroid belt). Production of the dust would require collisions between asteroids in a population corresponding to the
Kuiper Belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
around the Sun. Thus the dust is more likely created by a debris disk around Vega, rather than from a protoplanetary disk as was earlier thought. The inner boundary of the debris disk was estimated at , or 70–. 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 mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is b ...
. 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 The Palomar Testbed Interferometer (PTI) was a near infrared, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County, California, United States. It was built by Caltech and the Jet Propulsion Laboratory and w ...
by
David Ciardi David Robert Ciardi (born 17 July 1969) is an American astronomer. He received a bachelor's degree in physics and astronomy from Boston University in 1991, and a Ph.D. in physics from the University of Wyoming in 1997. Career Ciardi has publishe ...
and Gerard van Belle in 2001 and then later confirmed with the CHARA array at Mt. Wilson in 2006 and the Infrared Optical Telescope Array at Mt. Hopkins in 2011, revealed evidence for an inner dust band around Vega. Originating within of the star, this
exozodiacal dust Exozodiacal dust is 1–100 micrometre-sized grains of amorphous carbon and silicate dust that fill the plane of extrasolar planetary systems. It is the exoplanetary analog of zodiacal dust, the 1–100 micrometre-sized dust grains observed in ...
may be evidence of dynamical perturbations within the system. This may be caused by an intense bombardment of comets or meteors, and may be evidence for the existence of a planetary system.


Possible planets

Observations from the
James Clerk Maxwell Telescope The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength radio telescope at Mauna Kea Observatory in Hawaii, US. The telescope is near the summit of Mauna Kea at . Its primary mirror is 15 metres (16.4 yards) across: it is the larg ...
in 1997 revealed an "elongated bright central region" that peaked at 9″ () to the northeast of Vega. This was hypothesized as either a perturbation of the dust disk by a planet or else an orbiting object that was surrounded by dust. However, images by the
Keck telescope The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state In the United States, a state is a constituent political entit ...
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 The Joint Astronomy Centre (JAC) was a management organisation based in Hilo, Hawaii, which from c.1980-2015 operated two large telescopes at Mauna Kea Observatory on behalf of an international consortium from the United Kingdom, Canada and the N ...
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 clumps are caused by a roughly Jupiter-mass planet on an eccentric orbit. Dust would collect in orbits that have mean-motion resonances 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 clumps could be caused by a roughly
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
-mass planet having migrated from 40 to 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 on the
Subaru Telescope is the 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. It had the largest monolithic primary mirror in the wo ...
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 The Plateau de Bure Interferometer (PdBI) was a six-antenna interferometer on the Pic de Bure (2550 m) in the French Alps, operated by the Institut de radioastronomie millimétrique. In 2014, it has been replaced by the Northern Extended Mill ...
. 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. The smooth structure has been confirmed in follow-up observations by Hughes et al. (2012) and the
Herschel Space Telescope The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Teles ...
. Although a planet has yet to be directly observed around Vega, the presence of a planetary system cannot yet be ruled out. Thus there could be smaller, terrestrial planets orbiting closer to the star. The inclination of planetary orbits around Vega is likely to be closely aligned to the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
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 or Colmcille; gd, Calum Cille; gv, Colum Keeilley; non, Kolban or at least partly reinterpreted as (7 December 521 – 9 June 597 AD) was an Irish abbot and missionary evangelist credited with spreading Christianity in what is toda ...
constellation. In 2021, a paper analyzing 10 years of spectra of Vega detected a candidate 2.43-day signal around Vega, statistically estimated to have only a 1% chance of being a false positive. Considering the amplitude of the signal, the authors estimated a minimum mass of Earth masses, but considering the very oblique rotation of Vega itself of only 6.2° from Earth's perspective, the planet may be aligned to this plane as well, giving it an actual mass of Earth masses. The researchers also detected a faint -day signal which could translate to a Earth masses ( at 6.2° inclination) but is too faint to claim as a real signal with available data.


Etymology and cultural significance

The name is believed to be derived from the Arabic term ''Al Nesr al Waki'' النسر الواقع which appeared in the Al Achsasi al Mouakket star catalogue and was translated into Latin as ''Vultur Cadens'', "the falling eagle/vulture". The constellation was represented as a vulture in ancient Egypt, and as an eagle or vulture in ancient India. The Arabic name then appeared in the western world in the '' Alfonsine tables'', which were drawn up between 1215 and 1270 by order of King Alfonso X. Medieval
astrolabe An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستاره‌یاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclin ...
s of England and Western Europe used the names Wega and Alvaca, and depicted it and Altair as birds. Among the northern Polynesian 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. The
Assyrians Assyrian may refer to: * Assyrian people, the indigenous ethnic group of Mesopotamia. * Assyria, a major Mesopotamian kingdom and empire. ** Early Assyrian Period ** Old Assyrian Period ** Middle Assyrian Empire ** Neo-Assyrian Empire * Assyrian ...
named this pole star Dayan-same, the "Judge of Heaven", while in
Akkadian Akkadian or Accadian may refer to: * Akkadians, inhabitants of the Akkadian Empire * Akkadian language, an extinct Eastern Semitic language * Akkadian literature, literature in this language * Akkadian cuneiform Cuneiform is a logo- syllabi ...
it was Tir-anna, "Life of Heaven". In Babylonian astronomy, Vega may have been one of the stars named Dilgan, "the Messenger of Light". To the ancient Greeks, the constellation Lyra was formed from the harp of Orpheus, with Vega as its handle. For the Roman Empire, the start of autumn was based upon the hour at which Vega set below the horizon. In
Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of va ...
, (), meaning ''
Weaving Girl ''Weaving Girl'' is a 2009 Chinese film directed by Wang Quan'an. Wang's fourth feature film, ''Weaving Girl'' stars Wang's frequent collaborator and former partner, actress Yu Nan. Title According to director Wang Quan'an, the film's title, ''Wea ...
(asterism)'', refers to an asterism consisting of Vega, ε Lyrae and ζ1 Lyrae. Consequently, the Chinese name for Vega is (, en, the First Star of Weaving Girl). In Chinese mythology, there is a love story of
Qixi The Qixi Festival ( zh, 七夕), also known as the Qiqiao Festival ( zh, 七巧, links=no), is a Chinese festival celebrating the annual meeting of Zhinü and Niulang in Chinese mythology... The festival is celebrated on the seventh day of the ...
() in which Niulang (, Altair) and his two children (
β Aquilae Beta Aquilae, Latinized from β Aquilae, is a triple star system in the equatorial constellation of Aquila. It is visible to the naked eye as a point-like source with an apparent visual magnitude of 3.87. Based on parallax measurements ...
and
γ Aquilae Gamma Aquilae, Latinized from γ Aquilae, and formally known as Tarazed , is a star in the constellation of Aquila. It has an apparent visual magnitude of 2.712, making it readily visible to the naked eye at night. Parallax measurements ...
) are separated from their mother Zhinü (, lit. "weaver girl", Vega) who is on the far side of the river, the Milky Way. However, one day per year on the seventh day of the seventh month of the
Chinese lunisolar calendar The traditional Chinese calendar (also known as the Agricultural Calendar 曆; 农历; ''Nónglì''; 'farming calendar' Former Calendar 曆; 旧历; ''Jiùlì'' Traditional Calendar 曆; 老历; ''Lǎolì'', is a lunisolar calendar ...
,
magpie Magpies are birds of the Corvidae family. Like other members of their family, they are widely considered to be intelligent creatures. The Eurasian magpie, for instance, is thought to rank among the world's most intelligent creatures, and is one ...
s make a bridge so that Niulang and Zhinü can be together again for a brief encounter. The Japanese
Tanabata , also known as the Star Festival ( 星祭り, ''Hoshimatsuri''), is a Japanese festival originating from the Chinese Qixi Festival. It celebrates the meeting of the deities Orihime and Hikoboshi (represented by the stars Vega and Altair res ...
festival, in which Vega is known as ''Orihime'' (織姫), is also based on this legend. In Zoroastrianism, Vega was sometimes associated with Vanant, a minor divinity whose name means "conqueror". The indigenous
Boorong The Wergaia or Werrigia people are an Aboriginal Australian group in the Mallee and Wimmera regions of north-Western Victoria, made up of a number of clans. The people were also known as the Maligundidj (in the Wotjobaluk language) which means ...
people of northwestern Victoria, Australia, named it as ''Neilloan'', "the flying loan". In the ''
Srimad Bhagavatam The ''Bhagavata Purana'' ( sa, भागवतपुराण; ), also known as the ''Srimad Bhagavatam'', ''Srimad Bhagavata Mahapurana'' or simply ''Bhagavata'', is one of Hinduism's eighteen great Puranas (''Mahapuranas''). Composed in Sa ...
'', Shri Krishna tells
Arjuna Arjuna (Sanskrit: अर्जुन, ), also known as Partha and Dhananjaya, is a character in several ancient Hindu texts, and specifically one of the major characters of the Indian epic Mahabharata. In the epic, he is the third among Panda ...
, that among the Nakshatras he is Abhijit, which remark indicates the auspiciousness of this Nakshatra. Medieval
astrologer Astrology is a range of divinatory practices, recognized as pseudoscientific since the 18th century, that claim to discern information about human affairs and terrestrial events by studying the apparent positions of celestial objects. Dif ...
s counted Vega as one of the Behenian stars and related it to
chrysolite Chrysolite may refer to: * Peridot, a gem-quality olivine * Archaically, any of several green or yellow-green-coloured gemstones including ** Topaz, a silicate mineral of aluminium and fluorine ** Chrysoberyl, an aluminate of beryllium ** Zircon, ...
and
winter savory ''Satureja montana'' (winter savory or mountain savory), is a perennial, semi-evergreen herb in the family Lamiaceae, native to warm temperate regions of southern Europe, the Mediterranean, and Africa. It has dark green leaves and summer flowers ...
. Cornelius Agrippa listed its
kabbalistic Kabbalah ( he, קַבָּלָה ''Qabbālā'', literally "reception, tradition") is an esoteric method, discipline and Jewish theology, school of thought in Jewish mysticism. A traditional Kabbalist is called a Mekubbal ( ''Məqūbbāl'' "rece ...
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. W. H. Auden's 1933 poem " A Summer Night (to Geoffrey Hoyland)" famously opens with the couplet, "Out on the lawn I lie in bed,/Vega conspicuous overhead". Vega became the first star to have a car named after it with the French Facel Vega line of cars from 1954 onwards, and later on, in America,
Chevrolet Chevrolet ( ), colloquially referred to as Chevy and formally the Chevrolet Motor Division of General Motors Company, is an American automobile division of the American manufacturer General Motors (GM). Louis Chevrolet (1878–1941) and ous ...
launched the Vega in 1971. Other vehicles named after Vega include the ESA's Vega launch system and the Lockheed Vega aircraft.


Notes


References


External links

* * * {{Authority control A-type main-sequence stars Delta Scuti variables Circumstellar disks Hypothetical planetary systems Castor Moving Group Lyra (constellation) Lyrae, Alpha 7001 Durchmusterung objects Lyrae, 03 0721 172167 091262 Lambda Boötis stars Northern pole stars Vega