Epsilon Ophiuchi is a star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Ophiuchus

Ophiuchus

Ophiuchus is a large constellation located around the celestial equator. Its name is from the Greek "serpent-bearer", and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century...

. It has the traditional name Yed Posterior (and the star Delta Ophiuchi

Delta Ophiuchi

Delta Ophiuchi is a star in the constellation Ophiuchus. It has the traditional name Yed Prior ....

, with which it forms a naked eye

Naked eye

The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...

 optical double

Double star

In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...

, is Yed Prior).

The traditional name Yed is derived from Arabic

Arabic language

Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 meaning "the hand", and the two stars are the left hand of Ophiuchus (the Serpent Bearer) that holds the head of the serpent Serpens Caput. It was a member of indigenous Arabic asterism

Asterism (astronomy)

In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...

 al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser

Alpha Serpentis

Alpha Serpentis is a triple star system in the constellation Serpens, in its head . Alpha Serpentis has the proper names Unukalhai, from the Arabic عنق الحية ‘Unuq al-Ħayyah "the Serpent's Neck", and Cor Serpentis from the Latin "the Heart of the Serpent"...

 (Unukalhai), δ Ser

Delta Serpentis

Delta Serpentis is a star system in the constellation Serpens, in its head . It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , ε Ser , δ Oph , ε Oph , ζ Oph and γ Oph .According to the...

 (Qin, Tsin), ε Ser

Epsilon Serpentis

Epsilon Serpentis is a star in the constellation Serpens, in its head .It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , δ Ser , δ Oph , ε Oph , ζ Oph and γ Oph .According to the...

 (Ba, Pa), δ Oph

Delta Ophiuchi

Delta Ophiuchi is a star in the constellation Ophiuchus. It has the traditional name Yed Prior ....

 (Yed Prior), ζ Oph

Zeta Ophiuchi

Zeta Ophiuchi is a star located in the constellation of Ophiuchus. It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , δ Ser , ε Ser , δ Oph , ε Ser and γ Oph .According to the catalogue of stars...

 (Han) and γ Oph

Gamma Ophiuchi

Gamma Ophiuchi is a Class A4, fourth-magnitude star in the constellation Ophiuchus. Gamma Ophiuchi is a stellar system located about 95 light-years from Earth....

 (Tsung Ching).

According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, al-Nasaq al-Yamānī or Nasak Yamani were the title for two stars :δ Ser

Delta Serpentis

Delta Serpentis is a star system in the constellation Serpens, in its head . It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , ε Ser , δ Oph , ε Oph , ζ Oph and γ Oph .According to the...

 as Nasak Yamani I and ε Ser

Epsilon Serpentis

Epsilon Serpentis is a star in the constellation Serpens, in its head .It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , δ Ser , δ Oph , ε Oph , ζ Oph and γ Oph .According to the...

 as Nasak Yamani II (exclude this star, α Ser

Alpha Serpentis

Alpha Serpentis is a triple star system in the constellation Serpens, in its head . Alpha Serpentis has the proper names Unukalhai, from the Arabic عنق الحية ‘Unuq al-Ħayyah "the Serpent's Neck", and Cor Serpentis from the Latin "the Heart of the Serpent"...

, δ Oph

Delta Ophiuchi

Delta Ophiuchi is a star in the constellation Ophiuchus. It has the traditional name Yed Prior ....

, ζ Oph

Zeta Ophiuchi

Zeta Ophiuchi is a star located in the constellation of Ophiuchus. It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , δ Ser , ε Ser , δ Oph , ε Ser and γ Oph .According to the catalogue of stars...

 and γ Oph

Gamma Ophiuchi

Gamma Ophiuchi is a Class A4, fourth-magnitude star in the constellation Ophiuchus. Gamma Ophiuchi is a stellar system located about 95 light-years from Earth....

)

In Chinese

Chinese language

The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...

, , meaning Right Wall of Heavenly Market Enclosure

Heavenly Market enclosure

Tian Shi Yuan, the Heavenly Market Enclosure , is one of the San Yuan or Three enclosures. Stars and constellations of this group are visible during late summer and early autumn in the Northern Hemisphere . The summer triangle lies directly to the northwest.-Asterisms:The asterisms are :...

, refers to an asterism which is represent eleven old states in China which is marking the right borderline of the enclosure, consisting of ε Ophiuchi, β Herculis

Beta Herculis

Beta Herculis , which also has the name Kornephoros, is the brightest star in the constellation of Hercules. It has an apparent visual magnitude which varies between 2.76 and 2.81.Although β Herculis appears to the naked eye to be a single star, W. W...

, γ Herculis

Gamma Herculis

Gamma Herculis is a magnitude 3.74 binary star in the constellation Hercules. It is a giant star with a stellar classification of A9III that is located at a distance of about 195 light years from the Earth.-Name:...

, κ Herculis

Kappa Herculis

Kappa Herculis is a double star in the constellation Hercules. Traditional names that have been attributed to the star are "Marfik", "Marfak" or "Marsic", all of which come from the Arabic لمرفق Al-Mirfaq meaning "the elbow", a name it shares with Lambda Ophiuchi.- Properties :Kappa Herculis is a...

, γ Serpentis, β Serpentis

Beta Serpentis

Beta Serpentis is a star system in the constellation Serpens, in its head . It was a member of indigenous Arabic asterism al-Nasaq al-Sha'āmī, "the Northern Line" of al-Nasaqān "the Two Lines", along with β Her , γ Her and γ Ser .According to the catalogue of stars in the Technical Memorandum...

, α Serpentis

Alpha Serpentis

Alpha Serpentis is a triple star system in the constellation Serpens, in its head . Alpha Serpentis has the proper names Unukalhai, from the Arabic عنق الحية ‘Unuq al-Ħayyah "the Serpent's Neck", and Cor Serpentis from the Latin "the Heart of the Serpent"...

, δ Serpentis

Delta Serpentis

Delta Serpentis is a star system in the constellation Serpens, in its head . It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , ε Ser , δ Oph , ε Oph , ζ Oph and γ Oph .According to the...

, ε Serpentis

Epsilon Serpentis

Epsilon Serpentis is a star in the constellation Serpens, in its head .It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , δ Ser , δ Oph , ε Oph , ζ Oph and γ Oph .According to the...

, δ Ophiuchi

Delta Ophiuchi

Delta Ophiuchi is a star in the constellation Ophiuchus. It has the traditional name Yed Prior ....

 and ζ Ophiuchi

Zeta Ophiuchi

Zeta Ophiuchi is a star located in the constellation of Ophiuchus. It was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines"., along with α Ser , δ Ser , ε Ser , δ Oph , ε Ser and γ Oph .According to the catalogue of stars...

 . Consequently, ε Ophiuchi itself is known as , represent the state Chu

Chu (state)

The State of Chu was a Zhou Dynasty vassal state in present-day central and southern China during the Spring and Autumn period and Warring States Period . Its ruling house had the surname Nai , and clan name Yan , later evolved to surname Mi , and clan name Xiong...

(楚) (or Tsoo), together with φ Capricorni

Phi Capricorni

Phi Capricorni is a star in the constellation Capricornus. φ Capricorni is an orange K-type bright giant with an apparent magnitude of +5.17...

 (or 24 Capricorni

24 Capricorni

24 Capricorni is a star in the constellation Capricornus. 24 Capricorni is a M-type red giant with an apparent magnitude of +4.49. It is approximately 523 light years from Earth.-Chinese name:...

 in R.H.Allen's version) in Twelve States

Girl (Chinese constellation)

The Girl mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the northern mansions of the Black Tortoise.- Asterisms :...

(asterism).

Structure

Epsilon Ophiuchi is 108 light years from Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

(while Delta is 170, hence they are a mere optical double). It is a class G giant, which, unusually for such stars, is cyanogen-deficient and carbon-deficient.