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| Mizar (Zeta Ursae Majoris) | |
|---|---|
| Name | Mizar (Zeta Ursae Majoris) |
| Constellation | Ursa Major |
| Epoch | J2000 |
| App mag v | 2.23 |
| Distance | 86 ly |
| Spectral type | A2V + A2V |
| Radial velocity | -6 km/s |
| Names | Zeta Ursae Majoris, ζ UMa |
Mizar (Zeta Ursae Majoris) is a prominent multiple star system in the constellation Ursa Major, visible to the naked eye near Alcor (80 Ursae Majoris), and historically significant in observational astronomy, spectroscopy, and binary star studies. The system has been central to investigations by figures and institutions such as Giovanni Battista Hodierna, Giovanni Cassini, William Herschel, Friedrich Bessel, Edward Pickering, and observatories including Yerkes Observatory, Greenwich Observatory, Mount Wilson Observatory, and Palomar Observatory. Mizar's role in multiple catalogs—Messier catalog, Bayer designation, Hipparcos catalogue, Henry Draper Catalogue, and Bright Star Catalogue—links it to projects like Gaia mission, Hubble Space Telescope, Keck Observatory, Very Large Telescope, and Sloan Digital Sky Survey.
The Bayer designation ζ associates the star with Ursa Major as part of the Bayer designation system promulgated after Johann Bayer and incorporated in atlases like those by John Flamsteed and Hevelius. Traditional names and folk references connect Mizar to narratives recorded by chroniclers such as Ptolemy, Al-Sufi, Abu Ma'shar, and later compilers including Richard Hinckley Allen, Johannes Hevelius, and Johann Bayer. Mizar appears in catalogs compiled by Charles Messier, John Flamsteed, Friedrich Wilhelm Argelander, and modern surveys like Hipparcos and Gaia for parallax and proper motion, and it is often paired with Alcor (80 Ursae Majoris) in cultural tests of eyesight noted by writers including Pliny the Elder and observers from Ancient Greece to Medieval Islamic astronomy; scholars such as E. W. Maunder and Simon Newcomb discussed its inclusion in navigational lore used by mariners from Age of Discovery voyages under commanders like Christopher Columbus and Ferdinand Magellan.
Mizar is a hierarchical multiple system comprising visual and spectroscopic subsystems studied at facilities including Harvard College Observatory, University of Chicago, Caltech, Max Planck Institute for Astronomy, and teams led by researchers like Antonia Maury and Edward C. Pickering. The wide visual pair with Alcor (80 Ursae Majoris) contrasts with the resolved double components Mizar A and Mizar B, each of which is itself a spectroscopic binary, an architecture analogous to systems cataloged by Torres, Andersen & Giménez and investigated with instruments at Mount Wilson Observatory, Palomar Observatory, and interferometers operated by University of Cambridge and CHARA Array. Components designated A and B were first resolved by observers associated with Giovanni Battista Hodierna and later by Friedrich Bessel and rediscovered by Giovanni Cassini, while modern separations and component masses derive from techniques deployed at Keck Observatory, Very Large Telescope, Subaru Telescope, and interferometry projects supported by National Science Foundation and European Southern Observatory.
Mizar's spectroscopic binaries exhibit orbital periods measurable via radial velocities recorded by spectrographs at Lick Observatory, Yerkes Observatory, Royal Greenwich Observatory, and modern echelle instruments on Keck I and ESO 3.6m Telescope. The A subsystem has an orbital period of about 20.5 days and the B subsystem about 175 days, parameters refined alongside eccentricities and semimajor axes using methods formalized by S. A. Alexander and Karl Schwarzschild and applied in analyses published in journals such as Monthly Notices of the Royal Astronomical Society, Astronomy and Astrophysics, and The Astrophysical Journal. Long-term relative motion between A and B is monitored against proper motion data from Hipparcos and Gaia, while dynamical stability criteria reference frameworks by P. Eggleton and S. J. Aarseth and N-body integrations run on systems developed at institutions like Cambridge University and Princeton University.
The primary components are A-type main-sequence stars with spectral types around A2V, documented in the Henry Draper Catalogue and spectral atlases curated by Annie Jump Cannon, Antonia Maury, and later revised by researchers at Smithsonian Astrophysical Observatory and Cerro Tololo Inter-American Observatory. Spectroscopic studies revealed line profiles and rotational velocities measured using techniques from Arthur Eddington and equipment at Mount Wilson Observatory, while chemical abundances were compared to standards studied by Audouin Dollfus and groups at Max Planck Institute for Astrophysics. Photometry from Hipparcos and ground-based campaigns at Palomar Observatory provided magnitudes and color indices used alongside bolometric corrections from models produced by teams at Geneva Observatory and Padova Observatory. Measurements of mass, radius, temperature, and luminosity utilize stellar evolution models from Icko Iben, Gustav Hertzsprung, and Ejnar Hertzsprung and are cross-referenced with isochrones from Yonsei–Yale and MESA grids.
The formation scenarios for hierarchical multiples like Mizar draw on theories developed by Lyman Spitzer, Fred Hoyle, C. J. Lada, and computational studies by groups at Harvard–Smithsonian Center for Astrophysics, Max Planck Institute for Astronomy, and Jet Propulsion Laboratory. Proposed pathways include fragmenting protostellar disks described by Shu, Adams & Lizano and dynamical capture processes examined by Heggie and Kroupa. Evolutionary fate predictions reference mass transfer and angular momentum loss formulations from Peter Eggleton and binary stellar evolution codes maintained by STScI and teams behind Binary Star Evolution (BSE) packages, with long-term outcomes framed relative to populations studied in open clusters by researchers at European Southern Observatory and surveys such as Gaia-ESO Survey.
Mizar's first telescopic double record is often attributed to observers in the early modern period including Giovanni Battista Riccioli and Giovanni Cassini, while spectroscopic binarity was first detected in the late 19th century by teams at Harvard College Observatory under figures like Edward Pickering and Antonia Maury. The system figured in debates and demonstrations by William Herschel and in catalogs by John Herschel, and it served as a test case in the development of spectrographs by Angelo Secchi and Hermann Carl Vogel. Culturally, Mizar and Alcor (80 Ursae Majoris) appear in literature and myth compiled by Pliny the Elder, Ovid, Ibn al-Haytham, and modern writers like Carl Sagan, while ethnographic records document significance among societies described by Claude Lévi-Strauss and explorers such as Captain Cook and James Cook. The star continues to be used in outreach by institutions such as Smithsonian Institution, Royal Astronomical Society, American Astronomical Society, and planetaria including Hayden Planetarium and Griffith Observatory.
Category:Ursa Major Category:Multiple star systems