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| Dubhe (Alpha Ursae Majoris) | |
|---|---|
| Name | Dubhe (Alpha Ursae Majoris) |
| Epoch | J2000 |
| Constellation | Ursa Major |
| Ra | 11h 03m 43.67152s |
| Dec | +61° 45′ 03.7245″ |
| App mag v | 1.79 |
| Spectral type | K0III |
| Distance pc | 25.6 |
| Radial velocity | −9.0 |
Dubhe (Alpha Ursae Majoris) is a bright K-type giant star in the constellation Ursa Major, prominent as one of the stars forming the Big Dipper asterism and serving as a pole star indicator for the North Celestial Pole in precession calculations linked to Hipparchus and Al-Battani. It is a spectroscopic binary whose primary has evolved off the main sequence to a helium-burning giant phase, and its properties have been referenced in catalogs such as the Hipparcos catalogue, the Henry Draper Catalogue, and studies by the European Space Agency and the Keck Observatory. Dubhe's brightness and position have made it significant in navigation histories involving Vikings, Polynesians, and later Age of Exploration mariners like Ferdinand Magellan and James Cook.
The traditional name derives from the Arabic دُبَّة (dubba, "female bear") reflecting the star's role in representing the rump of the Great Bear in Greco-Arabic star lore preserved by authors such as Ptolemy and commentators in the Islamic Golden Age like Al-Sufi. The Bayer designation "Alpha Ursae Majoris" stems from Johann Bayer's 1603 Uranometria, while the Flamsteed numbering and catalog entries were formalized by John Flamsteed and later by Francis Baily. Modern standardized naming practices follow the conventions of the International Astronomical Union, whose Working Group on Star Names reviews historical usages alongside catalogs maintained by observatories including Royal Greenwich Observatory and institutions like the Smithsonian Astrophysical Observatory.
Dubhe's primary has a spectral classification of K0III, indicating a cool orange giant with effective temperature estimates from spectroscopic analyses by teams at Mount Wilson Observatory and McDonald Observatory. Its luminosity and radius determinations derive from angular diameter measurements performed with facilities such as the Very Large Telescope interferometer and radio observations at the Very Long Baseline Array, with inferred radius several tens of times that of the Sun and luminosity several hundred times solar. Stellar atmosphere models employed by researchers at Princeton University and Harvard–Smithsonian Center for Astrophysics fit metallicity and surface gravity consistent with an intermediate-mass star; asteroseismic constraints from missions like Kepler and surveys by Gaia further refine its mass and age estimates in the context of stellar evolution models developed at institutions including Max Planck Institute for Astronomy.
Dubhe is a spectroscopic binary system first recognized in radial velocity studies at Lick Observatory and later characterized using adaptive optics at Palomar Observatory and interferometry at CHARA Array. The resolved companion, cataloged in catalogs such as the Washington Double Star Catalog and observed with the Hubble Space Telescope, contributes to dynamical mass estimates that constrain models produced by research groups at Caltech and University of Cambridge. Historical astrometric measurements from the Yerkes Observatory and radial velocity work by Williamina Fleming and successors trace orbital elements that inform synthetic population studies at Instituto de Astrofísica de Canarias and Observatoire de Paris.
Parallax and proper motion determinations by the Hipparcos mission, refined by the Gaia data releases, place Dubhe at roughly 83 light-years from Earth with space motion relative to the Local Standard of Rest measured through spectroscopy at Keck Observatory and kinematic analyses published by teams at University of California, Berkeley and Carnegie Institution for Science. Its radial velocity and proper motion vectors have been used in studies of galactic dynamics by researchers associated with Max Planck Institute for Astrophysics and the Royal Astronomical Society, and its trajectory contributes to models of stellar population membership compared against moving groups cataloged by Eggen and later surveys conducted by LAMOST and RAdial Velocity Experiment (RAVE).
As an evolved K-type giant, Dubhe exemplifies post-main-sequence evolutionary stages predicted by stellar evolution codes from teams at Geneva Observatory and Yale University; its position on the Hertzsprung–Russell diagram alongside giants studied in open clusters such as Hyades and M67 informs convective mixing and mass-loss prescriptions debated at conferences hosted by International Astronomical Union commissions. Its binary nature allows dynamical mass constraints useful for calibrating isochrone models used by research groups at University of Oxford and University of Michigan, and its observed chemical abundances feed into galactic chemical evolution studies by collaborations at Max Planck Institute for Astrophysics and the European Southern Observatory.
Dubhe has been recorded since antiquity in works by Ptolemy and featured in star lore across cultures compiled by scholars such as Richard Hinckley Allen and E. W. Maunder; during the Age of Sail it was a navigation aid in manuals by John Davis and Nathaniel Bowditch. Its prominence in modern astronomy includes observation campaigns by Hipparcos, imaging by Hubble Space Telescope, and spectroscopic follow-ups at Keck Observatory that have been cited in literature from Nature and The Astrophysical Journal. Cultural references appear in literature and music cataloged by institutions like the Library of Congress and in planetarium programs curated by Royal Observatory Greenwich and Hayden Planetarium.
Category:K-type giants Category:Ursa Major