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| Dubhe | |
|---|---|
| Other names | Alpha Ursae Majoris A, HD 95689, HIP 54204, HR 4301 |
| Epoch | J2000 |
| Constellation | Ursa Major |
| Ra | 11h 03m 43.6715s |
| Dec | +61° 45′ 03.724″ |
| App mag v | 1.79 |
| Spectral type | K0III |
| Parallax | 26.54 mas |
| Dist pc | 37.7 |
| Abs mag v | −0.32 |
| Radius | ~22 R☉ |
| Mass | ~4 M☉ |
| Luminosity | ~200 L☉ |
| Gravity | log g ~2.5 |
| Temperature | ~4,900 K |
| Rotational velocity | ~2 km/s |
| Names | Alpha Ursae Majoris, HD 95689, HIP 54204, HR 4301 |
Dubhe Dubhe is the traditional proper name of the northern star commonly cataloged as Alpha Ursae Majoris A, a bright K-type giant in the constellation Ursa Major. It is one of the most prominent stars of the northern sky, forming part of the well-known asterism that includes the Big Dipper and serving as an important navigation and cultural marker across civilizations. Modern astrometry and spectroscopy have characterized it as a spectroscopic multiple with a luminous giant primary and several fainter companions, making it a frequent subject in stellar evolution and multiplicity studies.
The traditional name derives from Arabic and Persian traditions transmitted through medieval European star catalogs and atlases. Historic star cataloguers such as Ptolemy and Islamic astronomers influenced later Western works like those by Johannes Hevelius and John Flamsteed, whose numbering conventions intersect with designation systems used by the Henry Draper Catalogue and the Hipparcos mission. Modern catalog identifiers include Henry Draper Catalogue numbers, the Hipparcos catalog entry, and Bayer designations from Johann Bayer; the International Astronomical Union standardized proper names in the 21st century, linking traditional nomenclature with modern cataloging practices.
Spectral classification places the star as a K0III giant, indicative of a cool, orange-hued photosphere with an effective temperature near 4,900 K. Its visual magnitude around 1.8 ranks it among the brighter members of the northern sky, comparable in apparent brightness studies to stars listed in the Bright Star Catalogue and cross-referenced in the Hipparcos Catalogue. Parallax measurements from the Hipparcos and later astrometric solutions establish a distance near 37–38 parsecs, enabling calculation of an absolute magnitude and bolometric luminosity several hundred times that of the Sun, consistent with interferometric radius estimates and evolutionary models produced by groups at institutions like the European Southern Observatory and major university observatories.
Located at the head of the classical constellation, the star anchors the northern end of the pattern commonly known as the Big Dipper, an asterism historically recorded by Ptolemy and extensively depicted by Hevelius and later atlas makers. Its position relative to other notable Ursa Major members—such as the stars cataloged under Bayer letters, nearby giants cataloged in the Bright Star Catalogue, and companions resolved in surveys by Washington Double Star Catalog—makes it a reference point in celestial navigation traditions used by mariners like those in the Age of Exploration and in modern astrometry by missions including Gaia.
As a K-type giant, the star has evolved off the main sequence after exhausting core hydrogen, following evolutionary tracks computed by stellar modelers at institutions such as the Geneva Observatory and the Padova group. Mass estimates infer an intermediate-mass progenitor, and the star is currently on the red-giant branch or possibly in a core-helium-burning phase depending on detailed asteroseismic constraints from space observatories like Kepler and ground-based spectroscopic analyses. Surface abundances and gravity determinations from high-resolution spectroscopy, often obtained at observatories including Keck Observatory and the Very Large Telescope, inform comparisons to stellar evolution codes and yield age estimates compatible with intermediate-age Galactic disk populations studied by survey projects such as RAVE and LAMOST.
The star’s brightness and position near the pole have made it a fixture in myth, navigation, and astronomical catalogues across cultures, appearing in Arabic astronomy texts, Norse lore, and Chinese star maps. Early catalogues by Ptolemy and medieval Islamic astronomers were transmitted into Renaissance atlases by Tycho Brahe and Johannes Hevelius, while later star atlases and navigational charts used the asterism for direction finding during the Age of Discovery. In modern outreach, the star and its asterism serve as an introductory target in amateur astronomy guides and planetarium programs produced by institutions like the Royal Astronomical Society and the American Astronomical Society.
The object is the primary of a multiple system: high-resolution spectroscopy and long-term astrometry reveal at least one spectroscopic companion in a relatively close orbit and more distant optical or gravitationally bound components cataloged in double-star compilations such as the Washington Double Star Catalog. Historic measures by observers associated with the Royal Astronomical Society and modern adaptive optics imaging from instruments on Gemini Observatory and Subaru Telescope have constrained companion separations and mass ratios, contributing to statistical studies of multiplicity among evolved stars compiled by survey teams at institutions like CfA and Max Planck Institute for Astronomy.
Research on the star has ranged from interferometric radius measurements to spectroscopic abundance analyses and radial-velocity monitoring campaigns. Interferometry from facilities like the CHARA Array provided direct angular diameters feeding into luminosity and radius determinations, while spectroscopic time-series from groups at ESO and NOAO characterized the spectroscopic binary orbit and searched for pulsational variability analogous to red-giant oscillations investigated by missions such as CoRoT and Kepler. Surveys of chemically peculiar giants and Galactic structure projects have used its well-determined parameters as calibration points in studies by research centers including the European Space Agency and university astrophysics departments.
Category:K-type giants Category:Ursa Major