Delta Serpentis, Latinized from δ Serpentis, is a binary star system in the constellation Serpens, in its head (Serpens Caput). The light from the two stars in the system give a combined apparent magnitude of +3.80, which is bright enough to be visible to the naked eye. Based on parallax measurements, it is located at a distance of approximately 230 light years from the Sun. The system is moving closer with a radial velocity of ~42 km/s, and may come to within 35.23pc in 1.2 million years.
The primary, component A, is a yellow-white F-type subgiant with an apparent magnitude of +4.25. It is classified as a Delta Scuti type variable star and its magnitude varies by 0.04 with a period of 0.1557 days. Its binary companion, component B, is also an F-type subgiant which is slightly dimmer, with a magnitude of +5.2. A and B are separated by four arcseconds in the sky, and perform one orbit around their centre of mass once every 3,200 years.
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 (Unukalhai), ε Ser (Ba, Pa), δ Oph (Yed Prior), ε Oph (Yed Posterior), ζ Oph (Han) and γ Oph (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 as Nasak Yamani I and ε Ser as Nasak Yamani II (exclude α Ser, δ Oph, ε Oph, ζ Oph and γ Oph)
In Chinese, Chinese: 天市右垣 (Chinese: Tiān Shì Yòu Yuán), meaning Right Wall of Heavenly Market Enclosure, refers to an asterism which represents eleven old states in China and which marks the right borderline of the enclosure, consisting of δ Serpentis, β Herculis, γ Herculis, κ Herculis, γ Serpentis, β Serpentis, α Serpentis, ε Serpentis, δ Ophiuchi, ε Ophiuchi and ζ Ophiuchi.[1] Consequently, the Chinese name for δ Serpentis itself is Chinese: 天市右垣六 (Chinese: Tiān Shì Yòu Yuán liù, English: the Sixth Star of Right Wall of Heavenly Market Enclosure), representing the state Qin (秦) (or Tsin),[2] [3] [4] together with θ Capricorni and 30 Capricorni (according to Ian Ridpath version) in Twelve States (asterism).