What kind of star is Pollux?
Pollux, catalogued as Beta Geminorum (β Gem), appears in the official constellation Gemini. Its apparent visual magnitude is about 1.14, while its estimated distance is about 33.8 light-years. Astronomers classify the object as K0 III. 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.
Pollux has exhausted core hydrogen and expanded into a K0 giant while remaining only about 34 light-years from the Sun. Repeated radial-velocity measurements reveal a companion with a period near 590 days and a minimum mass several times Jupiter's; the planet's IAU-approved proper name is Thestias. Unlike Aldebaran's disputed signal, Pollux's velocity period remains coherent across long datasets and is distinguishable from measured rotation and magnetic-activity indicators. Spectropolarimetry detects a weak surface magnetic field, showing that even a slowly rotating giant can sustain organised magnetism. Interferometric angular-diameter measurements, combined with distance, tightly constrain the star's physical radius and help place it on evolutionary tracks.
The coordinate pair RA 07h 45m 18.95s, Dec +28° 01′ 34.3″ 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.
Pollux data at a glance
| Proper name | Pollux | Catalogue designation | Beta Geminorum (β Gem) |
|---|---|---|---|
| Constellation | Gemini | Apparent magnitude | about 1.14 |
| Spectral or system type | K0 III | Estimated distance | about 33.8 light-years |
| Right ascension (J2000) | 07h 45m 18.95s | Declination (J2000) | +28° 01′ 34.3″ |
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 Pollux
Named for Pollux, the immortal twin of Castor in Greek and Roman tradition.
Classical tradition made Pollux the immortal twin and Castor the mortal one, although the two naked-eye stars are unrelated in space. Bayer assigned Pollux the letter Beta despite its greater apparent brightness. The planetary name Thestias was approved through the IAU's 2015 NameExoWorlds campaign; it refers to Leda, mother of Pollux, through her patronymic. This modern naming layer is separate from the star's ancient Greek and Roman identity.
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 Pollux
Find Orion in winter and look northeast for Castor and Pollux. Pollux is the lower, more southerly and warmer-coloured member of the pair.
Best on northern winter and southern summer evenings; visible from most of the globe. 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
- Look northeast of Orion from December through April to find the Castor–Pollux pair.
- Pollux is the lower, more southerly twin and usually shows the warmer tint.
- Use binoculars to explore nearby open cluster M44 in Cancer after identifying Gemini.
- The planet Thestias is not directly visible; it is inferred from precision spectroscopy over many orbits.
Interesting facts about Pollux
- Pollux is brighter than Castor despite carrying the Bayer letter Beta.
- It is an evolved orange giant and one of the nearest familiar first-magnitude giants.
- Pollux hosts a confirmed giant planet whose approved proper name is Thestias.
- Pollux and Castor form the heads of the celestial Twins.
- Its warm colour is readily distinguishable from Castor’s whiter light.
Continue from Pollux into the night sky
Use the Gemini 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.