Epsilon1 Arae

Epsilon1 Arae (ε1 Ara, ε1 Arae) is the Bayer designation for a star in the constellation Ara, the Altar. It is visible to the naked eye with an apparent visual magnitude of +4.1 Based upon an annual parallax shift of 9.04 mas, this star is around 360 ly distant from the Earth.

ε1 Arae is an evolved giant star with a stellar classification of K3 III. It is around 74% more massive than the Sun. At an age of about 1.7 billion years, the outer envelope of the star has expanded to almost 34 times the Sun's radius. It is radiating energy into space at an effective temperature of 4,176 K, giving it the orange-hued glow of a K-type star.

ε1 Arae was known as 龜一(spelled as "Guī yī", meaning: "the 1st (star) of Guī") in traditional Chinese astronomy. Allen erroneously called it Tso Kang (左更). He probably confused the constellation "Ara" with "Ari", as Tso Kang is actually in Aries.