Epsilon Canis Majoris

Lore & Background

The primary, ε Canis Majoris A, has an apparent magnitude of +1.5 and belongs to spectral classification B2, with a blue or blueish-white color. Its exact evolutionary status is uncertain: spectroscopically it has been given class B2 II (bright giant), but it appears less luminous than expected and is more likely class B2 III-II. Two studies suggest it is still in the late main sequence, and one even suggested it could be the final product of a stellar merger. It has sufficient mass to explode as a supernova. The companion, ε Canis Majoris B, is magnitude +7.5 and lies 7.5″ away with a position angle of 161°; the primary is about 250 times brighter.

Reader's Guide

Epsilon Canis Majoris holds significance as the brightest source of extreme ultraviolet radiation in the night sky, making it a key star for understanding the ionization of interstellar gas near the Sun, particularly the Local Interstellar Cloud. Its historical brightness peak about 4.4–4.7 million years ago, when it was the brightest star in the night sky with a magnitude of −3.99 to −4.13, underscores the dynamic nature of stellar distances and apparent magnitudes. The system's binary nature, with a primary that may be a bright giant or a late main-sequence star, and its potential to end as a supernova, add to its astrophysical interest. Culturally, it appears on the national flag of Brazil, symbolizing the state of Tocantins, and a U.S. Navy cargo ship was named USS Adhara after the star. The IAU officially approved the name Adhara for the primary component in 2016.

Did You Know?

• About 4.7 million years ago, Epsilon Canis Majoris was the brightest star in the night sky with an apparent magnitude of −3.99.
• It is the brightest source of extreme ultraviolet radiation in the night sky.
• The primary star has a rotation period estimated to be about 5 days.
• The star appears on the national flag of Brazil, symbolising the state of Tocantins.