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| Alioth (Epsilon Ursae Majoris) | |
|---|---|
| Name | Alioth (Epsilon Ursae Majoris) |
| Epoch | J2000 |
| Constellation | Ursa Major |
| Apparent magnitude | 1.76 |
| Spectral type | A0pCr |
| Distance | ~81 ly |
| Other names | ε UMa, HD 112185, HR 4905, HIP 63090 |
Alioth (Epsilon Ursae Majoris) Alioth is the brightest star in the constellation of Ursa Major and one of the principal members of the Big Dipper asterism, notable for its role in celestial navigation and for being a well-studied chemically peculiar and variable star. It has been observed and cataloged by projects and institutions such as the Hipparcos mission, the Henry Draper Catalogue, the Harvard College Observatory, and the Royal Greenwich Observatory, and figures in the cultural traditions of societies including the Polynesians, Babylonians, and Maya.
The traditional name "Alioth" derives from the Arabic "al-yāthā" and appears alongside other historical star names recorded by figures and compilers such as Ptolemy, Al-Sufi, and Johannes Hevelius. Modern catalog designations include Bayer ε Ursae Majoris, Henry Draper HD 112185, Bright Star Catalogue HR 4905, and Hipparcos HIP 63090. Alioth's place within the Big Dipper links it to navigation tools used by Polynesian navigators, the Mariners' astrolabe, and later by explorers such as James Cook and Ferdinand Magellan.
Alioth is an A-type star with a high luminosity and a radius and mass greater than the Sun. Measurements from the Hipparcos and Gaia missions, combined with interferometry from facilities like the Very Large Telescope and historical photometry from the Mount Wilson Observatory, give an absolute magnitude and luminosity that place Alioth well above main-sequence red dwarfs cataloged in compilations by the American Association of Variable Star Observers and surveys by the Sloan Digital Sky Survey. Its effective temperature and surface gravity have been determined using spectral fitting methods employed by researchers at institutions such as the European Southern Observatory and the Max Planck Institute for Astronomy.
Alioth exhibits the spectral signatures of an Ap star and is classified in some catalogs as A0pCr, reflecting anomalous abundances of chromium and other elements. Spectroscopic analyses using instruments at the Keck Observatory, the William Herschel Telescope, and the Calar Alto Observatory have detected overabundances and stratification of elements that align with studies of chemically peculiar stars by groups at the Royal Observatory Edinburgh and the Observatoire de Paris. Line-profile studies reference techniques developed by astronomers at Cambridge University and University of Vienna, and comparisons are often made with well-known peculiar stars cataloged by Gerard Kuiper and Willem Luyten.
Alioth is an α2 Canum Venaticorum-type variable with rotational modulation of its light and spectral lines; photometric variability has been recorded by observers associated with the International Astronomical Union and monitoring campaigns coordinated through the American Association of Variable Star Observers and space missions including Hipparcos and TESS. Magnetic field measurements using spectropolarimeters at the Bernhard Schmidt Telescope and the Canada–France–Hawaii Telescope reveal a global organized field consistent with oblique rotator models developed by researchers at University of California, Berkeley and the University of St Andrews. Studies published by teams at Leiden University and Nicolaus Copernicus University relate Alioth's magnetic topology to processes discussed in works by Eugene Parker and Subrahmanyan Chandrasekhar.
Parallax determinations from the Hipparcos and Gaia catalogs place Alioth at approximately 81 light-years from the Solar System, with proper motion values reported in the Tycho and UCAC catalogs. Radial velocity and space motion studies connect Alioth kinematically to structures identified in surveys by the Radial Velocity Experiment and groups at the European Space Agency, and its motion is compared with moving groups and stellar streams like those studied by Gustav Strömberg and teams at the Harvard-Smithsonian Center for Astrophysics.
Stellar evolution models computed with codes from the Geneva Observatory and computational frameworks developed at Princeton University indicate that Alioth is a relatively young intermediate-mass star that has evolved partway across the main sequence. Isochrone fitting techniques used by researchers at University of Geneva and South African Astronomical Observatory estimate an age consistent with membership in populations traced by surveys such as the Geneva–Copenhagen Survey and modeled in the context of works by Icko Iben and Andre Maeder.
Alioth has been noted since antiquity in catalogs from Hipparchus through Ptolemy and appears in medieval star lists compiled by Al-Sufi and later European astronomers such as Tycho Brahe and Johannes Bayer. Its prominence in the Big Dipper made it a navigational marker for explorers including James Cook and featured in folklore collected by scholars like E. E. Evans-Pritchard and Jacob Grimm. Modern observational campaigns by observatories including the Cerro Tololo Inter-American Observatory and missions such as Hipparcos and Gaia continue to refine its parameters, while Alioth appears in cultural works from poetry anthologies archived by The British Library to star charts published by the Royal Astronomical Society.
Category:Stars