What kind of star is Alhena?
Alhena, catalogued as Gamma Geminorum (γ Gem), appears in the official constellation Gemini. Its apparent visual magnitude is about 1.93, while its estimated distance is about 109 light-years. Astronomers classify the object as A1 IV spectroscopic binary. 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.
Gamma Geminorum's visible primary is an A-type subgiant, slightly evolved beyond the main sequence and hotter than the Sun. Changes in its radial velocity reveal a close stellar companion, so measurements that treat Alhena as one isolated star can blur the properties of the system. The pair's orbit supplies mass constraints that cannot be obtained from a lone star as directly. Alhena is also a useful colour reference in Gemini: it appears whiter than orange Pollux. Its apparent membership in the Twins is geometric rather than genetic; Gemini's principal stars lie at different distances and include systems of very different ages and architectures.
The coordinate pair RA 06h 37m 42.71s, Dec +16° 23′ 57.4″ 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.
Alhena data at a glance
| Proper name | Alhena | Catalogue designation | Gamma Geminorum (γ Gem) |
|---|---|---|---|
| Constellation | Gemini | Apparent magnitude | about 1.93 |
| Spectral or system type | A1 IV spectroscopic binary | Estimated distance | about 109 light-years |
| Right ascension (J2000) | 06h 37m 42.71s | Declination (J2000) | +16° 23′ 57.4″ |
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 Alhena
Alhena derives from Arabic al-hanʿa, associated with a brand or mark on a camel and with an older Arabic lunar mansion. Its historical sky context is therefore broader than the modern Western Twins.
The name Alhena preserves an Arabic asterism and lunar-mansion association that did not map exactly onto modern Gemini. Greek tradition placed the star near a foot of Pollux, and Bayer labelled it Gamma Geminorum. Navigators also knew it as a bright reference star. IAU standardization fixes the spelling Alhena for Gamma Geminorum while the broader history explains why translations vary.
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 Alhena
Find Castor and Pollux, then trace Gemini's southern line through Wasat toward the bright point at Pollux's foot. Alhena is easily visible without optical aid and has a clean white appearance. Its close companion is detected spectroscopically, not as an easy visual double.
Visible from most of the world and especially prominent on northern winter and southern summer 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
- Best evening months are December through March.
- Trace southwest from Pollux through the body of Gemini.
- Compare Alhena's white light directly with orange Pollux.
- Do not expect the spectroscopic companion to split in a small telescope.
Interesting facts about Alhena
- Alhena is a close binary system.
- The visible primary is an A-type subgiant.
- Its name is connected with an old Arabic lunar mansion.
- It marks a foot in common drawings of Gemini.
- Its white colour contrasts noticeably with Pollux.
Continue from Alhena 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.