Tau Sagittarii

Tau Sagittarii (Tau Sgr, τ Sagittarii, τ Sgr) is a star in the southern zodiac constellation of Sagittarius.

Description
With an apparent visual magnitude of +3.3, this is one of the brighter members of the constellation. The distance of this star from Earth is roughly 122 ly, based upon parallax measurements.

This is a spectral type K1 giant star with about. The stellar envelope is slightly cooler than the Sun with an effective temperature of 4,459 K, giving the star a light orange color. The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 3.93 ± 0.04 mas, which, at its estimated distance, equates to a physical radius of about 16 times the radius of the Sun.

τ Sagittarii is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 54% lower than the sun's) and a high peculiar velocity (64 km/s, four times the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.

τ Sagittarii is a red clump giant, a star with a similar mass to the sun which has exhausted its core hydrogen, passed through the red giant branch, and started helium fusion in its core.

The Wow! signal
τ Sagittarii is the closest constellational star (a star that is part of the traditional outline of a constellation) to the origin of the 1977 Wow! signal.

Name and etymology

 * The star forms part of simple asterisms:
 * γ Sgr, τ Sgr, δ Sgr, ε Sgr, ζ Sgr, λ Sgr, σ Sgr and φ Sgr — the Teapot.
 * φ Sgr, τ Sgr, ζ Sgr, χ Sgr (double) and σ Sgr — the Returning Ostriches; in Arabic Al Naʽām al Ṣādirah often transliterated as Namalsadirah (النعم السادرة).
 * Originally four stars in a numerical order: φ Sgr, τ Sgr, χ1 Sgr and χ2 Sgr
 * ν Sgr, τ Sgr, ψ Sgr, ω Sgr, 60 Sgr and ζ Sgr, Al Udḥiyy — the Ostrich's Nest.
 * In the entirely separate Chinese tradition — 斗 (Dǒu), meaning Dipper: τ Sgr, φ Sgr, λ Sgr, μ Sgr, σ Sgr and ζ Sgr. The star itself is 斗宿五 (Dǒu Xiù wǔ, the Dipper's fifth star).