Epsilon Tauri (ε Tau / ε Tauri) is an orange giant star, spectral type of K0 III, located approximately 155 light-years away from the Sun in the constellation of Taurus. It is a member of the Hyades open cluster. It has the traditional names Ain (Arabic عين), or Oculus Borealis, both of which mean "eye". Another traditional name is Coronis (Greek Κορωνις), referring to one of the mythological Hyades sisters.

It has an 11th magnitude companion 182 arcseconds from the primary.

Since Epsilon Tauri lies near the plane of the ecliptic, it is sometimes occulted by the Moon and (very rarely) by planets.

As a member of the Hyades Cluster, Epsilon Tauri's age is well constrained at 625 million years. Given its large mass, this star was formerly a member of spectral type A that has now evolved off the main sequence into the giant phase. It is regarded as a red clump giant that burns helium at its core.

Planetary system

In 2007 a massive extrasolar planet was reported orbiting the star. The planet orbits Epsilon Tauri every 1.6 years in a somewhat eccentric orbit. At the time of the discovery it was the only known planet in an open cluster.. No other planets have yet been detected in the Hyades cluster, but another planetary system - Iota Horologii - was subsequently reassigned to the Hyades as a stellar family.