Tau Aquilae

Tau Aquilae (τ Aql, τ Aquilae) is the Bayer designation for a star in the equatorial constellation of Aquila. The apparent visual magnitude of 5.7 indicates it is a faint star that is visible to the naked eye from suburban skies; at least according to the Bortle Dark-Sky Scale. The annual orbital motion of the Earth causes a parallax shift of 7.06 mas, which means the distance to this star is approximately 460 light-years (140 parsecs). The magnitude of the star is diminished by 0.28 from extinction caused by interstellar gas and dust.

The spectrum of Tau Aquilae matches a stellar classification of K0 III, with the luminosity class of III suggesting this is an evolved giant star that has exhausted the supply of hydrogen at its core and left the main sequence of stars like the Sun. The measured angular diameter of this star is 1.08 ± 0.01 mas. At the estimated distance of this system, this yields a physical size of about 16.5 times the radius of the Sun. The outer envelope is radiating energy into space with an effective temperature of 4,660 K, giving it the orange hued glow of a K-type star.