Acamar, also known as Theta Eridani, is a double star, consisting of a +3.2 magnitude bright main star of the spectral class A4 and a companion of the spectral class A1 of magnitude +4.3. The angular separation of the stars amounts to 8.2". The distance from Earth is 120 light years.

In Star Trek, Acamar (or Theta Eridani) is a star system, consisting of binary companion stars, located about 162 light years from Sol. Acamar III was the third planet in the Acamar system and homeworld of the Acamarian species. It is ruled by Marouk, the Sovereign of Acamar III, as well as a planetary council. The Acamarians suffered through one hundred years of war between rival clans. In 2366 Marouk met with Brull, a leader of the Gatherers, the last renegade clan from Acamar III, in an effort to complete the re-integration of Acamarian society.

Brull took Marouk to meet with Chorgan, the supreme leader of the Gatherers. Unknown to Marouk her servant, Yuta, planned to kill Chorigan in revenge for the Gatherers' murder of her clan over a century prior. Yuta was killed by Riker before she could kill Chorgan. Eventually both Marouk and Chorgan were able to agree on a peace that would bring the Gatherers back into the Acamarian fold. (TNG: "The Vengeance Factor")