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Vega is the brightest
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
in the northern
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 first constellati ...
of Lyra. It has the
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
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 The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include moonlig ...
, 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 pole star around 12,000 BCE and will be so again around the year 13,727, when its
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. The declination angle is measured north (positive) or ...
will be . Vega was the first star other than the Sun to have its image and
spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
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 sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
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
main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
lifetimes. Compared with the Sun, Vega has a lower abundance of elements heavier than helium. Vega is also a variable star—that is, a star whose brightness fluctuates. It is rotating rapidly with a speed of at the equator. This causes the equator to bulge outward due to centrifugal effects, and, as a result, there is a variation of temperature across the star's photosphere that reaches a maximum at the poles. From Earth, Vega is observed from the direction of one of these poles. Based on observations of more
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
radiation than expected, Vega appears to have a circumstellar disk of
dust Dust is made of particle size, fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian processes, aeolian process), Types of volcan ...
. This dust is likely to be the result of collisions between objects in an orbiting
debris disk A debris disk (American English), or debris disc ( Commonwealth English), 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 ...
, which is analogous to the Kuiper belt in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
. Stars that display an infrared excess due to dust emission are termed Vega-like stars. Observations by the
James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope designed to conduct infrared astronomy. As the largest telescope in space, it is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, Lis ...
show that the disk is exceptionally smooth, with no evidence of shaping by massive planets, though there is some evidence that there may be one or more Neptune-mass planets closer to the star.


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 alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
. The traditional name ''Vega'' (earlier ''Wega'') comes from a loose transliteration of the
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
word ' (
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
: واقع) meaning "falling" or "landing", via the phrase ' (
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
: النّسر الْواقع), "the falling eagle". In 2016, the
International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
(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 The zenith (, ) is the imaginary point on the celestial sphere directly "above" a particular location. "Above" means in the vertical direction (Vertical and horizontal, plumb line) opposite to the gravity direction at that location (nadir). The z ...
in the mid-northern
latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
s 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 by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
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. The declination angle is measured north (positive) or ...
of +38.78°, Vega can only be viewed at latitudes north of 51° S. Therefore, it does not rise at all anywhere in
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
or in the southernmost part of South America, including Punta Arenas,
Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
(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 when it crosses the meridian at that time. Complementarily, Vega swoops down and kisses the horizon at true North at midnight on Dec 31/Jan 1, as seen from 51° N. 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 In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's Rotation around a fixed axis, rotational axis. In the absence of precession, the astronomical body's orbit would show ...
. 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 (Latinisation of names, Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an ...
, 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, and will peak in brightness in 290,000 years with an apparent magnitude of –0.81. This star lies at a vertex of a widely spaced asterism called the Summer Triangle, 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 Photography is the visual arts, art, application, and practice of creating images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is empl ...
of celestial objects, began in 1840 when John William Draper took an image of the
Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
using the daguerreotype process. On 17 July 1850, Vega became the first star (other than the Sun) to be photographed, when it was imaged by William Bond and John Adams Whipple at the
Harvard College Observatory The Harvard College Observatory (HCO) 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, United St ...
, also with a daguerreotype. In August 1872, Henry Draper took a photograph of Vega's
spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
, 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 A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
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 Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
orbits the Sun. Giuseppe Calandrelli noted stellar parallax in 1805-6 and came up with a 4-second value for the star which was a gross overestimate. 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'' astrometry 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 method used to display numerical data that spans a broad range of values, especially when there are significant differences among the magnitudes of the numbers involved. Unlike a linear Scale (measurement) ...
. This
apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
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 and several similar stars and averaged their brightness 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. 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 Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
, 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 The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high ...
. 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; 2,000–. However, the flux density of Vega drops rapidly in the
infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
, 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 Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
to
helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
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 and shed much of its mass, finally becoming a
white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
. 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 16.5 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 Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
process that combines
proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
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 A convection zone, convective zone or convective region of a star is a layer which is unstable due to convection. Energy is primarily or partially transported by convection in such a region. In a 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. 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 lines of hydrogen; specifically by the hydrogen Balmer series with the
electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
at the n=2 principal quantum number. The lines of other elements are relatively weak, with the strongest being ionized
magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
,
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
and chromium. The
X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
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 Coronal holes are regions of the Sun's corona that emit low levels of ultraviolet and X-ray radiation compared to their surroundings. They are composed of relatively cool and tenuous plasma (physics), plasma permeated by magnetic fields that are o ...
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 A magnetic field (sometimes called B-field) is a physical 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 ...
has been detected on the surface of Vega by a team of astronomers at the Observatoire du Pic du Midi. 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 gauss (G). 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 16.3 hours, much faster than the Sun's rotational period but similar to, and slightly slower than, those of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
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 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...
. Because of that, Vega is significantly oblate like those two planets. When the radius of Vega was measured to high accuracy with an interferometer, 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, 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 rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...
velocity for Vega is along the equator, much higher than the observed (i.e. projected) rotational velocity because Vega is seen almost pole-on. This is 88% of the speed that would cause the star to start breaking up from centrifugal effects. This rapid rotation of Vega produces a pronounced equatorial bulge, so the radius of the equator is 19% larger than the polar radius, compared to just under 11% for Saturn, the most oblate of the Solar System's planets. (The estimated polar radius of this star is
solar radii Solar may refer to: Astronomy * Of or relating to the Sun ** Solar telescope, a special purpose telescope used to observe the Sun ** A device that utilizes solar energy (e.g. "solar panels") ** Solar calendar, a calendar whose dates indicat ...
, 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 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. By the Von Zeipel theorem, the local luminosity is higher at the poles. As a result, if Vega were viewed along the plane of its
equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
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 number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of pro ...
s than helium are termed "metals". The metallicity of Vega's photosphere 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 Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
is slightly ''more'' abundant,
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
is only marginally less abundant and
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
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 and
scandium Scandium is a chemical element; it has Symbol (chemistry), symbol Sc and atomic number 21. It is a silvery-white metallic d-block, d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the lantha ...
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 Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
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 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 A convection zone, convective zone or convective region of a star is a layer which is unstable due to convection. Energy is primarily or partially transported by convection in such a region. In a radiation zone, energy is transported by radiation ...
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 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 is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
(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, 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 equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...
—the celestial equivalent of
longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...
—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. The declination angle is measured north (positive) or ...
, which is equivalent to a change in
latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
. 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. 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, 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 An open cluster is a type of star cluster made of tens 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 ...
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 (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
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
s 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 The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
.


Debris disks

By 2005, the Spitzer Space Telescope 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 The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...
). Production of the dust would require collisions between asteroids in a population corresponding to the Kuiper Belt around the Sun. Thus the dust is more likely created by a
debris disk A debris disk (American English), or debris disc ( Commonwealth English), 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 ...
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. 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 by David Ciardi 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 may be evidence of dynamical perturbations within the system. This may be caused by an intense bombardment of
comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
s or
meteor A meteor, known colloquially as a shooting star, is a glowing streak of a small body (usually meteoroid) going through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, creating a ...
s, and may be evidence for the existence of a planetary system. The disk was also observed with ALMA in 2020, the LMT in 2022 and with Hubble STIS and JWST MIRI in 2024. The ALMA image did resolve the outer disk for the first time. The Hubble observation is the first image of the disk in scattered light and found an outer halo made up of small dust grains. JWST observations also detected the Halo, the outer disk and for the first time the inner disk. The infrared observations also showed a gap at 60 AU for the first time. The dust interior of the outer disk is consistent with dust being dragged by the Poynting-Robertson effect. The inner edge of the inner disk is hidden behind the coronagraph, but it was inferred to be 3-5 AU from photometry. The star is also surrounded by hot infrared excess, located at the sub-AU region, leaving a second gap between the inner disk and the hot dust around the star. This hot infrared excess lies within about 0.2 AU or closer and is made up of small grains, like
graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...
and
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
and
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
oxides, which was previously verified.


Possible planets

Observations from the James Clerk Maxwell Telescope 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 A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...
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 in Hawaii and at
UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California, United States. Its academic roots were established in 1881 as a normal school then known as the southern branch of the C ...
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 and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...
-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 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 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. 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 planet A terrestrial planet, tellurian 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 accepted by the IAU are the inner planets closest to ...
s orbiting closer to the star. The inclination of planetary orbits around Vega is likely to be closely aligned to the
equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
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 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 Earth masses ( at 6.2° inclination) but is too faint to claim as a real signal with available data. Observations of the disk with JWST MIRI did find a very circular face-on disk. The morphology indicate that there is no planet more massive than
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 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...
beyond 10 AU. The disk has a gap at around 60 AU. Gap-opening planets are inferred for disks around other stars and the team tests this idea for Vega by running simulations. The simulations have shown that a planet with <6 at 65 AU would introduce interior asymetric structures that are not seen in the disk of Vega. Any gap-opening planet would need to be less massive. Additionally the inner edge of the inner disk was inferred to be 3-5 AU. Vega shows also evidence for hot infrared excess at the sub-AU region. The inner boundary of the warm debris might indicate that there is a
Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...
-mass planet inside, shepherding it.


Etymology and cultural significance

The name Vega is believed to be derived from the
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
term ''Al Nesr al Waki'' النسر الواقع which appeared in the Al Achsasi al Mouakket star catalogue and was translated into
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
as ''Vultur Cadens'', "the falling eagle/vulture". The constellation was represented as a vulture in
ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...
, and as an eagle or vulture in
ancient India Anatomically modern humans first arrived on the Indian subcontinent between 73,000 and 55,000 years ago. The earliest known human remains in South Asia date to 30,000 years ago. Sedentism, Sedentariness began in South Asia around 7000 BCE; ...
. The Arabic name then appeared in the
western world The Western world, also known as the West, primarily refers to various nations and state (polity), states in Western Europe, Northern America, and Australasia; with some debate as to whether those in Eastern Europe and Latin America also const ...
in the '' Alfonsine tables'', which were drawn up between 1215 and 1270 by order of King Alfonso X. Medieval astrolabes of
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
and
Western Europe Western Europe is the western region of Europe. The region's extent varies depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the Western half of the ancient Mediterranean ...
used the names Wega and Alvaca, and depicted it and Altair as birds. Among the northern
Polynesia Polynesia ( , ) is a subregion of Oceania, made up of more than 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are called Polynesians. They have many things in ...
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 The Pleiades (), also known as Seven Sisters and Messier 45 (M45), is an Asterism (astronomy), asterism of an open cluster, open star cluster containing young Stellar classification#Class B, B-type stars in the northwest of the constellation Tau ...
. A Hawaiian name is Keho‘oea; in
Native Hawaiian Native Hawaiians (also known as Indigenous Hawaiians, Kānaka Maoli, Aboriginal Hawaiians, or simply Hawaiians; , , , and ) are the Indigenous peoples of Oceania, Indigenous Polynesians, Polynesian people of the Hawaiian Islands. Hawaiʻi was set ...
culture objects can have different names depending on their position in the sky, so it is also known as Kahō‘eoa, Kaho‘ea or Keoe. The Assyrians named this pole star Dayan-same, the "Judge of Heaven", while in Akkadian it was Tir-anna, "Life of Heaven". In
Babylonian astronomy Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia. The numeral system used, sexagesimal, was based on 60, as opposed to ten in the modern decimal system. This system simplified the ca ...
, 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 Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of ...
, the start of autumn was based upon the hour at which Vega set below the horizon. In Chinese, (), meaning '' Weaving Girl (asterism)'', refers to an asterism consisting of Vega, ε Lyrae and ζ1 Lyrae. Consequently, the Chinese name for Vega is (, ). In
Chinese mythology Chinese mythology () is mythology that has been passed down in oral form or recorded in literature throughout the area now known as Greater China. Chinese mythology encompasses a diverse array of myths derived from regional and cultural tradit ...
, there is a love story of Qixi () in which Niulang (, Altair) and his two children ( β Aquilae and γ Aquilae) are separated from their mother Zhinü (, lit. "weaver girl", Vega) who is on the far side of the river, the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
. However, one day per year on the seventh day of the seventh month of the Chinese lunisolar calendar, magpies make a bridge so that Niulang and Zhinü can be together again for a brief encounter. The Japanese Tanabata festival, in which Vega is known as ''Orihime'' (織姫), is also based on this legend. In
Zoroastrianism Zoroastrianism ( ), also called Mazdayasnā () or Beh-dīn (), is an Iranian religions, Iranian religion centred on the Avesta and the teachings of Zoroaster, Zarathushtra Spitama, who is more commonly referred to by the Greek translation, ...
, Vega was sometimes associated with Vanant, a minor divinity whose name means "conqueror". The indigenous Boorong people of north-western Victoria, Australia, named it ''Neilloan'', "the flying
loan In finance, a loan is the tender of money by one party to another with an agreement to pay it back. The recipient, or borrower, incurs a debt and is usually required to pay interest for the use of the money. The document evidencing the deb ...
". In Indian astronomy and astrology, Vega is represented by the nakshatra Abhijit. In the '' Srimad Bhagavatam'', Shri Krishna tells Arjuna, that among the Nakshatras he is Abhijit, which remark indicates the auspiciousness of this Nakshatra.
Medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of World history (field), global history. It began with the fall of the West ...
astrologer Astrology is a range of Divination, divinatory practices, recognized as pseudoscientific since the 18th century, that propose that information about human affairs and terrestrial events may be discerned by studying the apparent positions ...
s counted Vega as one of the Behenian stars and related it to chrysolite and winter savory. Cornelius Agrippa listed its kabbalistic sign under ''Vultur cadens'', a literal Latin translation of the Arabic name. 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". In the 1997 film '' Contact'', the Vega system is the source of alien communication. 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 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 Lambda Boötis stars Circumstellar disks Hypothetical planetary systems Castor Moving Group Lyra Lyrae, Alpha 7001 BD+38 3238 Lyrae, 03 0721 172167 091262 Northern pole stars Stars with proper names