Adhara (Epsilon Canis Majoris)
Adhara (Epsilon Canis Majoris) is a star in the constellation Canis Major, magnitude 1.5.
Once the brightest star in Earth’s sky, by far — and still the strongest source of extreme ultraviolet we see.
Some four and a half million years ago, Adhara passed much closer to the Sun and blazed at about magnitude −4, as bright as Venus often appears. No star has looked so bright in our sky since, and none will for at least five million years.
Today it is a hot blue giant star, shining with about 38,700 times the Sun’s light from a surface at around 22,000 K. That heat makes it the brightest source of extreme ultraviolet light in our night sky. No star does more to strip electrons from the thin hydrogen gas near the Sun, so it plays a big part in shaping the nearby Local Interstellar Cloud. It is massive enough to end as a supernova — and one study suggests it may itself be the product of two stars merging.
Its name comes from the Arabic for ‘the virgins’, a group it formed with Wezen, Aludra and a fainter neighbour.
Adhara (Epsilon Canis Majoris) is 410 light-years away: the light we see from it set off around 1615, around the time Galileo first turned a telescope to the sky.
Did you know?
- A companion lost in the glare. A seventh-magnitude companion sits close beside Adhara, but the main star is about 250 times brighter, so only large telescopes can split the pair.
- On Brazil’s flag. Adhara appears on the national flag of Brazil, where it stands for the state of Tocantins.
- The Bow and Arrow. In Chinese astronomy Adhara is the seventh star of Hú Shǐ, the Bow and Arrow, a pattern that spans Canis Major and Puppis.
A bright blue-white star south of Sirius, marking the Great Dog’s hindquarters and forming a triangle with Wezen and Aludra. From mid-northern latitudes it stays low, so find a clear southern horizon.
When and where to see it
It is best placed in the evening sky around February, when it crosses the meridian at about 10 pm local time (around midnight in January). It can be seen from everywhere south of 61°N and never sets south of 61°S.
At its highest it stands 11° up from 50°N, 26° up from 35°N, 61° up from the equator, 84° up from 35°S.
Facts
- Type
- Star
- Constellation
- Canis Major
- Designations
- Epsilon Canis Majoris, ε CMa, 21 CMa, HR 2618, HD 52089, HIP 33579
- Magnitude
- 1.5
- Position
- RA 6h 58.6m, Dec −28° 58′ (J2000)
- Spectral type
- B1.5II
- Colour
- blue-white (B−V -0.21)
- Distance
- 410 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Adhara (Epsilon Canis Majoris) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.