Alpha Serpentis
Brightest star in Serpens, an orange giant about 74 light-years away.
Alpha Serpentis, also known as Unukalhai, is the brightest star in the constellation Serpens, located in the head (Serpens Caput). With an apparent visual magnitude of 2.6, it is visible to the naked eye from most of Earth. Parallax measurements place it at an estimated distance of about 74 light-years from the Sun.
Quick Facts
- Bayer designation
- α Serpentis
- Apparent visual magnitude
- 2.6
- Distance from sun
- about 74 ly
- Stellar classification
- K2IIIbCN1
- Mass
- 1.6 times the Sun
- Radius
- 13.5 times the Sun
- Effective temperature
- 4,687 K
Facts from the source article.
Properties
Alpha Serpentis is a giant star of spectral type K2IIIbCN1, having exhausted its core hydrogen and evolved off the main sequence. It has 1.6 times the Sun's mass and 13.5 times its radius, and is likely a horizontal branch or red clump star fusing helium into carbon and heavier elements. Its outer envelope temperature of 4,687 K gives it an orange hue typical of K-type stars. It is classified as a strong CN star, with unusually prominent cyanogen bands. The star radiates about 30 times the Sun's luminosity in visible light, with an additional 32 times the Sun's luminosity emitted in the infrared, for a total of about 70 times solar luminosity.
Nomenclature
The Bayer designation for this star is α Serpentis, Latinised to Alpha Serpentis. Its traditional names include Unukalhai (also spelled Unuk al Hay or Unuk Elhaija), from the Arabic عنق الحيّة (ʽunuq al-ḥayyah) meaning 'the serpent's neck', and Cor Serpentis, Latin for 'the Heart of the Serpent'. In 2016, the International Astronomical Union's Working Group on Star Names approved the name Unukalhai, and it is now listed in the IAU Catalog of Star Names. Alpha Serpentis is part of the indigenous Arabic asterism al-Nasaq al-Yamānī 'the Southern Line' of al-Nasaqān 'the Two Lines', along with Delta Serpentis, Epsilon Serpentis, Delta Ophiuchi, Epsilon Ophiuchi, Zeta Ophiuchi, and Gamma Ophiuchi. According to a 1971 NASA catalogue, al-Nasaq al-Yamānī or Nasak Yamani referred to two stars: Delta Serpentis as Nasak Yamani I and Epsilon Serpentis as Nasak Yamani II. In Chinese astronomy, it belongs to an asterism called 'Right Wall of Heavenly Market Enclosure', representing eleven old states, with Alpha Serpentis itself representing the state Shu (or Shuh), together with Lambda Serpentis in R.H. Allen's works.
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