Quasar
A quasar is an luminous active galactic nucleus. It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of times the mass of the Sun. In quasars and other types of AGN, the black hole is surrounded by a gaseous accretion disk; as gas falls toward the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum. The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way; the term "quasar" originated as a contraction of quasi-stellar radio source, because quasars were first identified during the 1950s as sources of radio-wave emission of unknown physical origin, when identified in photographic images at visible wavelengths they resembled faint star-like points of light. High-resolution images of quasars from the Hubble Space Telescope, have demonstrated that quasars occur in the centers of galaxies, that some host-galaxies are interacting or merging galaxies.
As with other categories of AGN, the observed properties of a quasar depend on many factors including the mass of the black hole, the rate of gas accretion, the orientation of the accretion disk relative to the observer, the presence or absence of a jet, the degree of obscuration by gas and dust within the host galaxy. Quasars are found over a broad range of distances, quasar discovery surveys have demonstrated that quasar activity was more common in the distant past; the peak epoch of quasar activity was 10 billion years ago. As of 2017, the most distant known quasar is ULAS J1342+0928 at redshift z = 7.54. The supermassive black hole in this quasar, estimated at 800 million solar masses, is the most distant black hole identified to date; the term "quasar" was first used in a paper by Chinese-born U. S. astrophysicist Hong-Yee Chiu in May 1964, in Physics Today, to describe certain astronomically-puzzling objects: So far, the clumsily long name'quasi-stellar radio sources' is used to describe these objects.
Because the nature of these objects is unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form'quasar' will be used throughout this paper. Between 1917 and 1922, it became clear from work by Heber Curtis, Ernst Öpik and others, that some objects seen by astronomers were in fact distant galaxies like our own, but when radio astronomy commenced in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation. The objects emitted large amounts of radiation of many frequencies, but no source could be located optically, or in some cases only a faint and point-like object somewhat like a distant star; the spectral lines of these objects, which identify the chemical elements of which the object is composed, were extremely strange and defied explanation. Some of them changed their luminosity rapidly in the optical range and more in the X-ray range, suggesting an upper limit on their size no larger than our own Solar System.
This implies an high power density. Considerable discussion took place over, they were described as "quasi-stellar radio sources", or "quasi-stellar objects", a name which reflected their unknown nature, this became shortened to "quasar". The first quasars were discovered as radio sources in all-sky radio surveys, they were first noted as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a small angular size. Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for their optical counterparts. In 1963, a definite identification of the radio source 3C 48 with an optical object was published by Allan Sandage and Thomas A. Matthews. Astronomers had detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum, which contained many unknown broad emission lines; the anomalous spectrum defied interpretation.
British-Australian astronomer John Bolton made many early observations of quasars, including a breakthrough in 1962. Another radio source, 3C 273, was predicted to undergo five occultations by the Moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to find a visible counterpart to the radio source and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar; this spectrum revealed the same strange emission lines. Schmidt was able to demonstrate that these were to be the ordinary spectral lines of hydrogen redshifted by 15.8 percent - an extreme redshift never seen in astronomy before. If this was due to the physical motion of the "star" 3C 273 was receding at an enormous velocity, around 47,000 km/s, far beyond the speed of any known star and defying any obvious explanation. Nor would an extreme velocity help to explain 3C 273's huge radio emissions. Although it raised many questions, Schmidt's discovery revolutionized quasar observation.
The strange spectrum of 3C 48 was identified by Schmidt and Oke as hydrogen and magnesium redshifted by 37%. Shortly afterwards, two more quasar spectra in 1964 and five more in 1965, were confirmed as ordinary
Corona
A corona is an aura of plasma that surrounds the Sun and other stars. The Sun's corona extends millions of kilometres into outer space and is most seen during a total solar eclipse, but it is observable with a coronagraph; the word corona is a Latin word meaning "crown", from the Ancient Greek κορώνη. Spectroscopy measurements indicate strong ionization in the corona and a plasma temperature in excess of 1,000,000 kelvins, much hotter than the surface of the Sun. Light from the corona comes from the same volume of space; the K-corona is created by sunlight scattering off free electrons. The F-corona is created by sunlight bouncing off dust particles, is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the E-corona is due to spectral emission lines produced by ions that are present in the coronal plasma. In 1724, French-Italian astronomer Giacomo F. Maraldi recognized that the aura visible during a solar eclipse belongs to the Sun not to the Moon.
In 1809, Spanish astronomer José Joaquín de Ferrer coined the term'corona'. Based in his own observations of the 1806 solar eclipse at Kinderhook, de Ferrer proposed that the corona was part of the Sun and not of the Moon. English astronomer Norman Lockyer identified the first element unknown on Earth in the Sun's chromosphere, called helium. French astronomer Jules Jenssen noted that the size and shape of the corona changes with the sunspot cycle. In 1930, Bernard Lyot invented the coronograph, which allows to see the corona without a total eclipse. In 1952, American astronomer Eugene Parker proposed that the solar corona might be heated by myriad tiny'nanoflares', miniature brightenings resembling solar flares that would occur all over the surface of the Sun; the high temperature of the Sun's corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a unknown element, "coronium". Instead, these spectral features have since been explained by ionized iron.
Bengt Edlén, following the work of Grotrian, first identified the coronal spectral lines in 1940 as transitions from low-lying metastable levels of the ground configuration of ionised metals. The sun's corona is much hotter than the visible surface of the Sun: the photosphere's average temperature is 5800 kelvins compared to the corona's one to three million kelvins; the corona is 10−12 times as dense as the photosphere, so produces about one-millionth as much visible light. The corona is separated from the photosphere by the shallow chromosphere; the exact mechanism by which the corona is heated is still the subject of some debate, but possibilities include induction by the Sun's magnetic field and magnetohydrodynamic waves from below. The outer edges of the Sun's corona are being transported away due to open magnetic flux and hence generating the solar wind; the corona is not always evenly distributed across the surface of the sun. During periods of quiet, the corona is more or less confined to the equatorial regions, with coronal holes covering the polar regions.
However, during the Sun's active periods, the corona is evenly distributed over the equatorial and polar regions, though it is most prominent in areas with sunspot activity. The solar cycle spans 11 years, from solar minimum to the following minimum. Since the solar magnetic field is continually wound up due to the faster rotation of mass at the sun's equator, sunspot activity will be more pronounced at solar maximum where the magnetic field is more twisted. Associated with sunspots are coronal loops, loops of magnetic flux, upwelling from the solar interior; the magnetic flux pushes the hotter photosphere aside, exposing the cooler plasma below, thus creating the dark sun spots. Since the corona has been photographed at high resolution in the X-ray range of the spectrum by the satellite Skylab in 1973, later by Yohkoh and the other following space instruments, it has been seen that the structure of the corona is quite varied and complex: different zones have been classified on the coronal disc.
The astronomers distinguish several regions, as described below. Active regions are ensembles of loop structures connecting points of opposite magnetic polarity in the photosphere, the so-called coronal loops, they distribute in two zones of activity, which are parallel to the solar equator. The average temperature is between two and four million kelvins, while the density goes from 109 to 1010 particle per cm3. Active regions involve all the phenomena directly linked to the magnetic field, which occur at different heights above the Sun's surface: sunspots and faculae, occur in the photosphere, spicules, Hα filaments and plages in the chromosphere, prominences in the chromosphere and transition region, flares and coronal mass ejections happen in the corona and chromosphere. If flares are violent, they can perturb the photosphere and generate a Moreton wave. On the contrary, quiescent prom
Rayleigh scattering
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. Rayleigh scattering is, hence, a parametric process; the particles may be individual molecules. It can occur when light travels through transparent solids and liquids, is most prominently seen in gases. Rayleigh scattering results from the electric polarizability of the particles; the oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle therefore becomes a small radiating dipole; this radiation is an integral part of the photon and no excitation or deexcitation occurs. Rayleigh scattering of sunlight in Earth's atmosphere causes diffuse sky radiation, the reason for the blue color of the daytime and twilight sky, as well as the yellowish to reddish hue of the low Sun. For wave frequencies well below the resonance frequency of the scattering particle, the amount of scattering is inversely proportional to the fourth power of the wavelength.
Rayleigh scattering of molecular nitrogen and oxygen in the atmosphere includes elastic scattering as well as the inelastic contribution from rotational Raman scattering in air, since the changes in wavenumber of the scattered photon are smaller than 50 cm−1. This can lead to changes in the rotational state of the molecules. Furthermore, the inelastic contribution has the same wavelengths dependency as the elastic part. Scattering by particles similar to, or larger than, the wavelength of light is treated by the Mie theory, the discrete dipole approximation and other computational techniques. Rayleigh scattering applies to particles that are small with respect to wavelengths of light, that are optically "soft". On the other hand, anomalous diffraction theory applies to larger particles. In 1859, while attempting to determine whether any contaminants remained in the purified air he used for infrared experiments, John Tyndall discovered that bright light scattering off nanoscopic particulates was faintly blue-tinted.
He conjectured that a similar scattering of sunlight gave the sky its blue hue, but he could not explain the preference for blue light, nor could atmospheric dust explain the intensity of the sky's color. In 1871, Lord Rayleigh published two papers on the color and polarization of skylight to quantify Tyndall's effect in water droplets in terms of the tiny particulates' volumes and refractive indices. In 1881 with the benefit of James Clerk Maxwell's 1865 proof of the electromagnetic nature of light, he showed that his equations followed from electromagnetism. In 1899, he showed that they applied to individual molecules, with terms containing particulate volumes and refractive indices replaced with terms for molecular polarizability; the size of a scattering particle is parameterized by the ratio where r is its characteristic length and λ is the wavelength of the light. The amplitude of light scattered from within any transparent dielectric is proportional to the inverse square of its wavelength and to the volume of material, to the cube of its characteristic length.
The wavelength dependence is characteristic of dipole scattering and the volume dependence will apply to any scattering mechanism. Objects with x ≫ 1 act as geometric shapes. At the intermediate x ≃ 1 of Mie scattering, interference effects develop through phase variations over the object's surface. Rayleigh scattering applies to the case when the scattering particle is small and the whole surface re-radiates with the same phase; because the particles are randomly positioned, the scattered light arrives at a particular point with a random collection of phases. In detail, the intensity I of light scattered by any one of the small spheres of diameter d and refractive index n from a beam of unpolarized light of wavelength λ and intensity I0 is given by where R is the distance to the particle and θ is the scattering angle. Averaging this over all angles gives the Rayleigh scattering cross-sectionThe fraction of light scattered by a group of scattering particles is the number of particles per unit volume N times the cross-section.
For example, the major constituent of the atmosphere, has a Rayleigh cross section of 5.1×10−31 m2 at a wavelength of 532 nm. This means that at atmospheric pressure, where there are about 2×1025 molecules per cubic meter, about a fraction 10−5 of the light will be scattered for every meter of travel; the strong wavelength dependence of the scattering means that shorter wavelengths are scattered more than longer wavelengths. The expression above can be written in terms of individual molecules by expressing the dependence on refractive index in terms of the molecular polarizability α, proportional to the dipole moment induced by the electric field of the light. In this case, the Rayleigh scattering intensity for a single particle is given in CGS-units by When the dielectric constant ϵ of a certain region of volume V is different from the average dielectric constant of the medium ϵ ¯ {\displaystyle
Coronagraph
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view the corona of the Sun, but a new class of conceptually similar instruments are being used to find extrasolar planets and circumstellar disks around nearby stars; the coronagraph was introduced in 1931 by the French astronomer Bernard Lyot. Coronagraphs operating within Earth's atmosphere suffer from scattered light in the sky itself, due to Rayleigh scattering of sunlight in the upper atmosphere. At view angles close to the Sun, the sky is much brighter than the background corona at high altitude sites on clear, dry days. Ground-based coronagraphs, such as the High Altitude Observatory's Mark IV Coronagraph on top of Mauna Loa, use polarization to distinguish sky brightness from the image of the corona: both coronal light and sky brightness are scattered sunlight and have similar spectral properties, but the coronal light is Thomson-scattered at nearly a right angle and therefore undergoes scattering polarization, while the superimposed light from the sky near the Sun is scattered at only a glancing angle and hence remains nearly unpolarized.
Coronagraph instruments are extreme examples of stray light rejection and precise photometry because the total brightness from the solar corona is less than one millionth the brightness of the Sun. The apparent surface brightness is fainter because, in addition to delivering less total light, the corona has a much greater apparent size than the Sun itself. During a total solar eclipse, the Moon acts as an occluding disk and any camera in the eclipse path may be operated as a coronagraph until the eclipse is over. More common is an arrangement where the sky is imaged onto an intermediate focal plane containing an opaque spot. Another arrangement is to image the sky onto a mirror with a small hole: the desired light is reflected and reimaged, but the unwanted light from the star goes through the hole and does not reach the detector. Either way, the instrument design must take into account scattering and diffraction to make sure that as little unwanted light as possible reaches the final detector.
Lyot's key invention was an arrangement of lenses with stops, known as Lyot stops, baffles such that light scattered by diffraction was focused on the stops and baffles, where it could be absorbed, while light needed for a useful image missed them. As an example, imaging instruments on the Hubble Space Telescope offer coronagraphic capability. A band-limited coronagraph uses; this mask is designed to block light and manage diffraction effects caused by removal of the light. The band-limited coronagraph has served as the baseline design for the canceled Terrestrial Planet Finder coronagraph. Band-limited masks will be available on the James Webb Space Telescope. See also: A phase-mask coronagraph uses a transparent mask to shift the phase of the stellar light in order to create a self-destructive interference, rather than a simple opaque disc to block it. See also: An optical vortex coronagraph uses a phase-mask in which the phase-shift varies azimuthally around the center. Several varieties of optical vortex coronagraphs exist: the scalar optical vortex coronagraph based on a phase ramp directly etched in a dielectric material, like fused silica.
The vector vortex coronagraph employs a mask that rotates the angle of polarization of photons, ramping this angle of rotation has the same effect as ramping a phase-shift. A mask of this kind can be synthesized by various technologies, ranging from liquid crystal polymer, micro-structured surfaces; such a vector vortex coronagraph made out of liquid crystal polymers is in use at the 200-inch Hale telescope at the Palomar Observatory. It has been operated with adaptive optics to image extrasolar planets; this works with stars other than the sun because they are so far away their light is, for this purpose, a spatially coherent plane wave. The coronagraph using interference masks out the light along the center axis of the telescope, but allows the light from off axis objects through. Coronagraphs in outer space are much more effective than the same instruments would be if located on the ground; this is because the complete absence of atmospheric scattering eliminates the largest source of glare present in a terrestrial coronagraph.
Several space missions such as NASA-ESA's SOHO, NASA's SPARTAN, Solar Maximum Mission, Skylab have used coronagraphs to study the outer reaches of the solar corona. The Hubble Space Telescope is able to perform coronagraphy using the Near Infrared Camera and Multi-Object Spectrometer, there are plans to have this capability on the James Webb Space Telescope using its Near Infrared Camera and Mid Infrared Instrument. While space-based coronagraphs such as LASCO avoid the sky brightness problem, they face design challenges in stray light management under the stringent size and weight requirements of space flight. Any sharp edge causes Fresnel diffraction of incoming light around the edge, which means that the smaller instruments that one would want on a satellite unavoidably leak more light than larger ones would; the LASCO C-3 coronagraph uses both an exte
Moon
The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, the largest among planetary satellites relative to the size of the planet that it orbits; the Moon is after Jupiter's satellite Io the second-densest satellite in the Solar System among those whose densities are known. The Moon is thought to have formed not long after Earth; the most accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. The Moon is in synchronous rotation with Earth, thus always shows the same side to Earth, the near side; the near side is marked by dark volcanic maria that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. After the Sun, the Moon is the second-brightest visible celestial object in Earth's sky, its surface is dark, although compared to the night sky it appears bright, with a reflectance just higher than that of worn asphalt.
Its gravitational influence produces the ocean tides, body tides, the slight lengthening of the day. The Moon's average orbital distance is 1.28 light-seconds. This is about thirty times the diameter of Earth; the Moon's apparent size in the sky is the same as that of the Sun, since the star is about 400 times the lunar distance and diameter. Therefore, the Moon covers the Sun nearly during a total solar eclipse; this matching of apparent visual size will not continue in the far future because the Moon's distance from Earth is increasing. The Moon was first reached in September 1959 by an unmanned spacecraft; the United States' NASA Apollo program achieved the only manned lunar missions to date, beginning with the first manned orbital mission by Apollo 8 in 1968, six manned landings between 1969 and 1972, with the first being Apollo 11. These missions returned lunar rocks which have been used to develop a geological understanding of the Moon's origin, internal structure, the Moon's history. Since the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft.
Both the Moon's natural prominence in the earthly sky and its regular cycle of phases as seen from Earth have provided cultural references and influences for human societies and cultures since time immemorial. Such cultural influences can be found in language, lunar calendar systems and mythology; the usual English proper name for Earth's natural satellite is "the Moon", which in nonscientific texts is not capitalized. The noun moon is derived from Old English mōna, which stems from Proto-Germanic *mēnô, which comes from Proto-Indo-European *mḗh₁n̥s "moon", "month", which comes from the Proto-Indo-European root *meh₁- "to measure", the month being the ancient unit of time measured by the Moon; the name "Luna" is used. In literature science fiction, "Luna" is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of Earth's moon; the modern English adjective pertaining to the Moon is lunar, derived from the Latin word for the Moon, luna. The adjective selenic is so used to refer to the Moon that this meaning is not recorded in most major dictionaries.
It is derived from the Ancient Greek word for the Moon, σελήνη, from, however derived the prefix "seleno-", as in selenography, the study of the physical features of the Moon, as well as the element name selenium. Both the Greek goddess Selene and the Roman goddess Diana were alternatively called Cynthia; the names Luna and Selene are reflected in terminology for lunar orbits in words such as apolune and selenocentric. The name Diana comes from the Proto-Indo-European *diw-yo, "heavenly", which comes from the PIE root *dyeu- "to shine," which in many derivatives means "sky and god" and is the origin of Latin dies, "day"; the Moon formed 4.51 billion years ago, some 60 million years after the origin of the Solar System. Several forming mechanisms have been proposed, including the fission of the Moon from Earth's crust through centrifugal force, the gravitational capture of a pre-formed Moon, the co-formation of Earth and the Moon together in the primordial accretion disk; these hypotheses cannot account for the high angular momentum of the Earth–Moon system.
The prevailing hypothesis is that the Earth–Moon system formed after an impact of a Mars-sized body with the proto-Earth. The impact blasted material into Earth's orbit and the material accreted and formed the Moon; the Moon's far side has a crust, 30 mi thicker than that of the near side. This is thought to be; this hypothesis, although not perfect best explains the evidence. Eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, Jeff Taylor challenged fellow lunar scientists: "You have eighteen months. Go back to your Apollo data, go back to your computer, do whatever you have to, but make up your mind. Don't come to our conference unless you have something to say about the Moon's birth." At the 1984 conference at Kona, the giant impact hypothesis emerged as the most consensual theory. Before the conference, there were parti
Fomalhaut
Fomalhaut designated Alpha Piscis Austrini is the brightest star in the constellation of Piscis Austrinus and one of the brightest stars in the sky. It is a class A star on the main sequence 25 light-years from the Sun as measured by the Hipparcos astrometry satellite. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified, it is classified as a Vega-like star that emits excess infrared radiation, indicating it is surrounded by a circumstellar disk. Fomalhaut, K-type main-sequence star TW Piscis Austrini, M-type, red dwarf star LP 876-10 constitute a triple system though the companions are separated by several degrees. Fomalhaut holds a special significance in extrasolar planet research, as it is the center of the first stellar system with an extrasolar planet candidate imaged at visible wavelengths; the image was published in Science in November 2008. Fomalhaut is the third-brightest star known to have a planetary system, after the Pollux.
Α Piscis Austrini is the system's Bayer designation. It bears the Flamsteed designation of 24 Piscis Austrini; the classical astronomer Ptolemy put it in Aquarius, as well as Piscis Austrinus. In the 1600s Johann Bayer planted it in the primary position of Piscis Austrinus. Following Ptolemy, John Flamsteed in 1725 additionally denoted it 79 Aquarii; the current designation reflects modern consensus on Bayer's decision, that the star belongs in Piscis Austrinus. Under the rules for naming objects in multiple star systems, the three components – Fomalhaut, TW Piscis Austrini and LP 876-10 – are designated A, B and C, respectively. On its discovery, the planet was designated Fomalhaut b; the star's traditional name derives from Fom al-Haut from scientific Arabic فم الحوت fam al-ḥūt "the mouth of the Fish", a translation of how Ptolemy labeled it. In 2016, the International Astronomical Union organized a Working Group on Star Names 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 the name Fomalhaut for this star.
In July 2014, the International Astronomical Union launched a process for giving proper names to certain exoplanets. The process involved public voting for the new names. In December 2015, the IAU announced; the winning name was proposed by Todd Vaccaro and forwarded by the St. Cloud State University Planetarium of St. Cloud, United States of America, to the IAU for consideration. Dagon was a Semitic deity represented as half-man, half-fish. At a declination of −29.6°, Fomalhaut is located south of the celestial equator, hence is best viewed from the Southern Hemisphere. However, its southerly declination is not as great as that of stars such as Acrux, Alpha Centauri and Canopus, meaning that, unlike them, Fomalhaut is visible from a large part of the Northern Hemisphere as well, its declination is similar to that of Antares. At 40°N, Fomalhaut rises above the horizon for eight hours and reaches only 20° above the horizon, while Capella, which rises at the same time, will stay above the horizon for twenty hours.
Fomalhaut can be located in northern latitudes by the fact that the western side of the Square of Pegasus points to it. Continuing the line from Beta to Alpha Pegasi towards the southern horizon, Fomalhaut is about 45˚ south of Alpha Pegasi, with no bright stars in between. Fomalhaut is a young star, for many years thought to be only 100 to 300 million years old, with a potential lifespan of a billion years. A 2012 study gave a higher age of 440±40 million years; the surface temperature of the star is around 8,590 K. Fomalhaut's mass is about 1.92 times that of the Sun, its luminosity is about 16.6 times greater, its diameter is 1.84 times as large. Fomalhaut is metal-deficient compared to the Sun, which means it is composed of a smaller percentage of elements other than hydrogen and helium; the metallicity is determined by measuring the abundance of iron in the photosphere relative to the abundance of hydrogen. A 1997 spectroscopic study measured a value equal to 93% of the Sun's abundance of iron.
A second 1997 study deduced a value of 78%, by assuming Fomalhaut has the same metallicity as the neighboring star TW Piscis Austrini, which has since been argued to be a physical companion. In 2004, a stellar evolutionary model of Fomalhaut yielded a metallicity of 79%. In 2008, a spectroscopic measurement gave a lower value of 46%. Fomalhaut has been claimed to be one of 16 stars belonging to the Castor Moving Group; this is an association of stars which share a common motion through space, have been claimed to be physically associated. Other members of this group include Vega; the moving group has an estimated age of 200±100 million years and originated from the same location. More recent work has found that purported members of the Castor Moving Group appear to not only have a wide range of ages, but their velocities are too different to have been associated with one another in the distant past. Hence, "membership" to this dynamical group has no bearing on the age of the Fomalhaut system. Fomalhaut is surrounded by several debris disks.
The inner disk is a high-carbon small-grain ash disk, clustering at 0.1 AU from the star. Next is a disk of larger particles, with inner edge 0.4-1 AU of the star. The innermost dis
