Theta1 Eridani


Distance (Light Years) 161 ± 4
Apparent Magnitude 2.88(Combined)
Color (B-V)0.14

Names For This Star

According to Allen, this star, Theta Eridani, was originally recognized as the end of the River Eridanus and therefore bore the name Achernar. This name now applies to Alpha Eridani instead.

According to Allen, the first usage of the name "Acamar" for this star was in the Alfonsine Tables published in Spain in 1252 under the patronage of King Alfonso X of Leon and Castile. However, Allen gives no information about the origin of the name.

Description of the Star

Acamar is a binary star system. The primary, Acamar A, is an A4III normal giant. This star is much hotter than the sun and white in color. Even though the smaller star is technically a dwarf, both stars are larger in mass and radius than our sun.

The smaller star is about one magnitude dimmer than the larger star and lies about 8.31 arc seconds away from it. At the distance of the star system from the earth, this separation corresponds to more than 5 times the diameter of the solar system out to Pluto.

According to Burnham a very slow orbital motion has been observed for the companion relative to the primay. This is consistent with the large separation between the stars.

Other Designations For This Star

Hipparcos Identifier (HIP Number)


Harvard Revised (HR Number)


Henry Draper Catalog (HD Number)


Bonner Durchmusterung (BD Number)

CD-40 771
Smithsonian Astrophysical
Observatory compendium (SAO Number)

Fundamental Katalog (FK5 Number)



Copyright © 1998 - 2010 by Arnold V. Lesikar,
Professor Emeritus
Dept. of Physics, Astronomy, and Engineering Science,
St. Cloud State University,St. Cloud, MN 56301-4498

Feedback to: editor AT