What kind of star is Mizar?
Mizar, catalogued as Zeta Ursae Majoris Aa (ζ UMa Aa), appears in the official constellation Ursa Major. Its apparent visual magnitude is about 2.23 for Mizar; 2.0 with Alcor, while its estimated distance is about 83 light-years. Astronomers classify the object as A-type quadruple system; wider pairing with Alcor. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Mizar is a hierarchical quadruple system: the visually separated Mizar A and B subsystems are each spectroscopic binaries. Nearby Alcor is itself a binary. The Mizar and Alcor systems share motion and distance as members of the Ursa Major Moving Group; whether their very wide configuration is best described as securely bound has been analysed through modern astrometry. Mizar A made history as the first spectroscopic binary discovered, when periodic doubling of its spectral lines exposed orbital motion. These nested scales—from days to centuries and beyond—make the field a compact demonstration of stellar dynamics.
The coordinate pair RA 13h 23m 55.54s, Dec +54° 55′ 31.3″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Mizar data at a glance
| Proper name | Mizar | Catalogue designation | Zeta Ursae Majoris Aa (ζ UMa Aa) |
|---|---|---|---|
| Constellation | Ursa Major | Apparent magnitude | about 2.23 for Mizar; 2.0 with Alcor |
| Spectral or system type | A-type quadruple system; wider pairing with Alcor | Estimated distance | about 83 light-years |
| Right ascension (J2000) | 13h 23m 55.54s | Declination (J2000) | +54° 55′ 31.3″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Mizar
Mizar comes from Arabic miʾzar, “girdle” or “waistcloth.” The IAU applies the name specifically to Zeta Ursae Majoris Aa.
Mizar and Alcor have long served as an eyesight test in several cultural traditions, though claims about a single universal military test are too sweeping. Giovanni Battista Riccioli documented Mizar’s telescopic double in 1650. Photography of the pair followed in the nineteenth century, and Antonia Maury’s spectral work helped establish Mizar A as the first known spectroscopic binary. The IAU later reserved Mizar for component Aa, while Alcor remains a separately named system.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Mizar
Mizar is the middle star in the Big Dipper’s handle. Sharp unaided eyes can see fainter Alcor beside it; binoculars make that pair effortless. A small telescope then splits Mizar itself into two bright points, while spectroscopy reveals that each is also binary.
Circumpolar through much of the Northern Hemisphere; especially prominent on spring evenings. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Choose the middle bend of the Big Dipper’s handle and first look for Alcor unaided.
- Binoculars easily separate Mizar and Alcor by about 12 arcminutes.
- A small telescope at 40–80× splits Mizar A and B into a bright, nearly equal-looking pair.
- The inner spectroscopic pairs cannot be visually resolved with ordinary amateur equipment.
Interesting facts about Mizar
- Mizar was the first telescopic double star known from an early documented observation.
- Mizar A became the first star recognized as a spectroscopic binary.
- Both Mizar A and Mizar B are themselves binaries, making Mizar a quadruple system.
- Alcor is also binary and shares the Ursa Major Moving Group’s motion.
- The official name Mizar applies to component Aa.
Continue from Mizar into the night sky
Use the Ursa Major constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.