Gamma Sagittarii

Gamma Sagittarii

Location of γ Sagittarii (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Sagittarius
Right ascension	18h 05m 48.48810s
Declination	–30° 25′ 26.7235″
Apparent magnitude (V)	+2.98
Characteristics
Spectral type	K1 III
U−B color index	+0.77
B−V color index	+1.01
Astrometry
Radial velocity (Rv)	22.0 km/s
Proper motion (μ)	RA: –53.92 mas/yr Dec.: -180.90 mas/yr
Parallax (π)	33.67 ± 0.18 mas
Distance	96.9 ± 0.5 ly (29.7 ± 0.2 pc)
Details
Radius	12 R☉
Surface gravity (log g)	2.72 cgs
Temperature	4,760 K
Metallicity [Fe/H]	–0.36 dex
Other designations
Alnasl, Nushaba, Warida, γ Sagittarii, γ Sgr, Gamma Sgr, 10 Sagittarii, CPD-30  5241, FK5 679, GC 24632, HD 165135, HIP 88635, HR 6746, PPM 297231, SAO 209696,
Database references
SIMBAD	data

Gamma Sagittarii (Gamma Sgr, γ Sagittarii, γ Sgr) is a 3rd-magnitude star in the zodiac constellation Sagittarius. The location of this star forms the tip of the arrow in the bow of Sagittarius the Centaur. It has the proper names Alnasl (Nasl, El Nasl), Nushaba (Nash) and Warida.

This star is close enough to the Earth that its distance can be determined using parallax, yielding a value of about 96.9 light-years (29.7 parsecs). It has an apparent visual magnitude of +2.98, making it the seventh brightest star in the constellation. A stellar classification of K1 III reveals that this is a giant star, having expanded to an estimated 12 times the Sun's radius. This means it has exhausted the hydrogen in its core and evolved away from the main sequence. The abundance of elements other than hydrogen and helium in this star, what astronomers term the star's metallicity, is lower than in the Sun. Gamma Sagittarii has an effective temperature of 4,760 K, compared to 5,778 K for the Sun. It is this lower temperature that gives Gamma Sagittarii the orange hue that is a characteristic of K-type stars.

There is a fainter optical companion located about 50 arcminutes north of this star. It is magnitude 4.7 Cepheid variable star designated W Sagittarii.

Name and etymology

• Alnasl is derived from the Arabic النصل al-naşl meaning "arrowhead"., Nushaba is derived from the Arabic Zujj al-Nashshaba meaning the same as Alnasl., Warida is derived from النعم الوارد Al Naʽām al Wārid, the Going Ostriches, the asterism consisting this star, δ Sgr, ε Sgr and η Sgr.
• This star, together with :
  • δ Sgr, ε Sgr, ζ Sgr, λ Sgr, σ Sgr, τ Sgr and φ Sgr, comprising the asterism Teapot.
  • δ Sgr and ε Sgr were Akkadian Sin-nun‑tu, or Si-nu-nu‑tum, the Swallow.
• In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Waridah, which was translated into Latin as Prima τού al Warida, meaning first going ostrich.
• In Chinese, 箕 (Jī), meaning Winnowing Basket, refers to an asterism consisting of γ Sagittarii, δ Sagittarii, ε Sagittarii and η Sagittarii. Consequently, γ Sagittarii itself is known as 箕宿一 (Jī Sù yī, English: the First Star of Winnowing Basket.)