What kind of star is Unukalhai?
Unukalhai, catalogued as Alpha Serpentis (α Ser), appears in the official constellation Serpens. Its apparent visual magnitude is about 2.63, while its estimated distance is about 74 light-years. Astronomers classify the object as K2 III orange giant. 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.
Unukalhai is an evolved K-type giant. After consuming core hydrogen, it expanded to a radius many times the Sun’s and cooled enough to appear orange, while remaining substantially more luminous overall. Its spectrum is used to determine metallicity and atmospheric composition, and radial-velocity monitoring has investigated variability without producing the kind of famous, securely characterized system associated with Pollux. The star’s modest distance makes its luminosity better constrained than that of remote supergiants. Visually, it is isolated enough to serve as a reliable guide through Serpens Caput’s compact triangular head.
The coordinate pair RA 15h 44m 16.08s, Dec +06° 25′ 32.3″ 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.
Unukalhai data at a glance
| Proper name | Unukalhai | Catalogue designation | Alpha Serpentis (α Ser) |
|---|---|---|---|
| Constellation | Serpens | Apparent magnitude | about 2.63 |
| Spectral or system type | K2 III orange giant | Estimated distance | about 74 light-years |
| Right ascension (J2000) | 15h 44m 16.08s | Declination (J2000) | +06° 25′ 32.3″ |
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 Unukalhai
Unukalhai comes from Arabic ʿunuq al-ḥayya, “the serpent’s neck.” The alternative Cor Serpentis, “heart of the serpent,” reflects a different anatomical placement.
Serpens is unique among the 88 IAU constellations because Ophiuchus divides it into two disconnected sky areas, Serpens Caput and Serpens Cauda. The Arabic proper name locates Alpha Serpentis at the serpent’s neck; Latin atlases also called it Cor Serpentis, the heart. Bayer’s Alpha designation correctly identifies the constellation’s brightest star. The IAU retained the spelling Unukalhai when formalizing traditional names.
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 Unukalhai
Find the northern half of Serpens west of Ophiuchus. Unukalhai is the brightest star in Serpens Caput and has a noticeable warm tint in binoculars. The constellation is split into Head and Tail regions, but both remain one official IAU constellation.
Visible from nearly all inhabited latitudes; best during northern summer and southern winter. 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
- Begin at Rasalhague, then move southwest into the small Serpens Caput pattern.
- Use binoculars to appreciate the star’s orange tint against fainter white neighbours.
- Remember that Serpens Caput and Cauda are one constellation separated by Ophiuchus.
- Observe near the meridian from northern latitudes for the darkest background and best colour impression.
Interesting facts about Unukalhai
- Unukalhai is the brightest star in the entire constellation Serpens.
- It is an orange giant that has left the main sequence.
- Its name means the serpent’s neck.
- The historical alternative Cor Serpentis means the serpent’s heart.
- Serpens is the only IAU constellation represented by two non-contiguous regions.
Continue from Unukalhai into the night sky
Use the Serpens 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.