# Unukalhai (Alpha Serpentis)

Unukalhai (Alpha Serpentis) is a star in the constellation Serpens, magnitude 2.6.

**The serpent’s neck — brightest star of the only constellation cut in two.**

Serpens is the only constellation split in two: Ophiuchus, the serpent-bearer, grips the snake in the middle, with its head on one side and its tail on the other. Unukalhai shines in the head half. Its name is Arabic for “the serpent’s neck”, and in Latin it was Cor Serpentis, “the heart of the serpent”.

It is an [orange](https://astropilot.space/glossary/star-colour) giant of about 1.6 times the Sun’s mass. It has used up the hydrogen in its core and probably now fuses helium there, swollen to 13.5 times the Sun’s width with a surface near 4,700 K. Its spectrum shows unusually strong bands of cyanogen, a molecule of carbon and nitrogen, which marks it out as a “CN star”.

Unukalhai (Alpha Serpentis) is 74 light-years away: the light we see from it set off in 1952, 5 years before Sputnik became the first artificial satellite.

## Did you know?

- **The Southern Line.** Arabic star lore placed it in al-Nasaq al-Yamānī, “the Southern Line”, a string of stars across Serpens and Ophiuchus that includes Yed Prior and Zeta Ophiuchi.
- **The state of Shu.** In Chinese astronomy it is the seventh star of the Right Wall of the Heavenly Market Enclosure, where it stands for Shu, one of the old states of China.

An orange star of magnitude 2.6, the brightest in Serpens; binoculars bring out its colour. Follow fainter stars about 9 degrees north to the Serpent’s head, a small group of stars just south of Corona Borealis.

## When and where to see it

It is best placed in the evening sky around June, when it crosses the meridian at about 10 pm local time (around midnight in May). It can be seen from everywhere north of 84°S and never sets north of 84°N.

At its highest it stands 46° up from 50°N, 61° up from 35°N, 84° up from the equator, 49° up from 35°S.

## Facts

- Type: Star
- Constellation: Serpens
- Designations: Alpha Serpentis, α Ser, 24 Ser, HR 5854, HD 140573, HIP 77070
- Magnitude: 2.6
- Position: RA 15h 44.3m, Dec +6° 26′ (J2000)
- Spectral type: K2IIIbCN1
- Colour: orange (B−V 1.17)
- Distance: 74 light-years
- Discovered: Known since antiquity

Open AstroPilot to see when Unukalhai (Alpha Serpentis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view. https://astropilot.space/object/unukalhai