What kind of star is Alioth?
Alioth, catalogued as Epsilon Ursae Majoris (ε UMa), appears in the official constellation Ursa Major. Its apparent visual magnitude is 1.76, while its estimated distance is about 83 light-years. Astronomers classify the object as A1 III–IVp; magnetic chemically peculiar. 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.
Epsilon Ursae Majoris is a magnetic chemically peculiar A star and the prototype of neither a pulsating nor eclipsing variable. Instead, elements such as chromium and europium are distributed unevenly across its atmosphere under the influence of a global magnetic field. As the star rotates in roughly 5.1 days, these abundance patches change the spectrum and produce slight brightness variations classified with Alpha2 Canum Venaticorum variables. Alioth also shares space motion and age with the Ursa Major moving group, along with several central Dipper stars. Membership is based on three-dimensional velocity and stellar properties, not simply participation in the same sky pattern; Dubhe and Alkaid are notable visual members that do not share the group's motion.
The coordinate pair RA 12h 54m 01.75s, Dec +55° 57′ 35.4″ 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.
Alioth data at a glance
| Proper name | Alioth | Catalogue designation | Epsilon Ursae Majoris (ε UMa) |
|---|---|---|---|
| Constellation | Ursa Major | Apparent magnitude | 1.76 |
| Spectral or system type | A1 III–IVp; magnetic chemically peculiar | Estimated distance | about 83 light-years |
| Right ascension (J2000) | 12h 54m 01.75s | Declination (J2000) | +55° 57′ 35.4″ |
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 Alioth
From an Arabic name commonly connected with alyat, the broad or fatty part of a sheep’s tail, reflecting an older sky figure.
Alioth's name passed through Arabic catalogue traditions and referred to part of an older animal figure rather than the modern Bear alone. Bayer assigned Epsilon Ursae Majoris, although it is the constellation's brightest star. Its reliable naked-eye visibility led to selection in navigational star lists. Twentieth-century spectroscopy revealed changing chemical lines and magnetic behaviour, explaining why a star used as a steady guide can still vary slightly on a five-day rotation cycle.
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 Alioth
Alioth is the first handle star moving away from the Big Dipper’s bowl, directly beside Megrez. It is easy to see without optical aid throughout the year at many northern latitudes.
Strongly northern and circumpolar across much of northern Europe and North America. 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
- Find the first handle star immediately beside the Big Dipper's bowl.
- At high northern latitudes it is circumpolar and available in every season.
- Use multicolour calibrated photometry to detect the subtle rotational variation.
- Compare the shared motion of central Dipper stars conceptually; it is not visible in one observing session.
Interesting facts about Alioth
- Alioth is the brightest star in Ursa Major despite its Epsilon designation.
- It is a magnetic chemically peculiar star whose spectrum and brightness change slightly as it rotates.
- Alioth belongs to the Ursa Major Moving Group of stars sharing motion and origin.
- Five central Big Dipper stars share this relationship, while end stars Dubhe and Alkaid do not.
- Alioth is one of the stars historically selected for celestial navigation.
Continue from Alioth 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.