Epsilon Eridani

Epsilon Eridani (Latinized from ε Eridani), proper name Ran, is a star in the southern constellation of Eridanus. At a declination of −9.46°, it is visible from most of Earth's surface. Located at a distance 10.5 light-years (3.2 parsecs) from the Sun, it has an apparent magnitude of 3.73, making it the third-closest individual star (or star system) visible to the naked eye.

The star is estimated to be less than a billion years old. This relative youth gives Epsilon Eridani a higher level of magnetic activity than the Sun, with a stellar wind 30 times as strong. The star's rotation period is 11.2 days at the equator. Epsilon Eridani is smaller and less massive than the Sun, and has a lower level of elements heavier than helium. It is a main-sequence star of spectral class K2, with an effective temperature of about 5,000 K (8,500 °F), giving it an orange hue. It is a candidate member of the Ursa Major moving group of stars, which share a similar motion through the Milky Way, implying these stars shared a common origin in an open cluster.

Periodic changes in Epsilon Eridani's radial velocity have yielded evidence of a giant planet orbiting it, designated Epsilon Eridani b. The discovery of the planet was initially controversial, but most astronomers now regard the planet as confirmed. In 2015 the planet was given the proper name AEgir [sic]. The Epsilon Eridani planetary system also includes a debris disc consisting of a Kuiper belt analogue at 70 au from the star and warm dust between about 3 au and 20 au from the star. The gap in the debris disc between 20 and 70 au implies the likely existence of outer planets in the system.

As one of the nearest Sun-like stars, Epsilon Eridani has been the target of several observations in the search for extraterrestrial intelligence. Epsilon Eridani appears in science fiction stories and has been suggested as a destination for interstellar travel. From Epsilon Eridani, the Sun would appear as a star in Serpens, with an apparent magnitude of 2.4.