Phi Aquarii

Phi Aquarii (φ Aqr, φ Aquarii) is the Bayer designation for a binary star system in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of +4.223. Parallax measurements from the Hipparcos mission indicate its estimated distance from Earth is roughly 220 light-years (67 parsecs).

This is a spectroscopic binary star system with an estimated period of 2,500 days. The primary component is a red giant star with a stellar classification of M1.5 III. The outer envelope of this evolved star has expanded to 39 times the size of the Sun. It is radiating 324 times the luminosity of the Sun at an effective temperature of 3,899 K, giving it the reddish hue of an M-type star.