Mirzam (Beta Canis Majoris)
Mirzam (Beta Canis Majoris) is a star in the constellation Canis Major, magnitude 2.0.
The Herald that rises before Sirius — and was once brighter than Sirius is today.
Its name means “the Herald” in Arabic, probably because it climbs above the horizon just ahead of Sirius, announcing the brightest star in the sky. But the herald once outshone its master. Around four million years ago Mirzam was the brightest star in Earth’s night sky — more than seven times as bright as Sirius is now.
It is a hot blue-white giant of 12 to 13 solar masses, its surface near 24,700 kelvin, over four times hotter than the Sun’s. Only 12 to 14 million years old, it has already begun to swell, and it is heavy enough to end its life as a supernova.
Mirzam also breathes. Its outer layers pulse in three overlapping rhythms, each about six hours long, making it a Beta Cephei variable star. The change is far too slight for the eye to notice.
Mirzam (Beta Canis Majoris) is 490 light-years away: the light we see from it set off around 1535, around the time Copernicus put the Sun at the centre of the Solar System.
Did you know?
- On Brazil’s flag. Mirzam is one of the stars on the flag of Brazil, where it stands for the state of Amapá.
- A misplaced pheasant. The Dunhuang Star Chart from China shows it as Yeji, the “Pheasant Cock” — drawn about 10 degrees too far north.
- Its own tunnel. Mirzam lies inside the Mirzam Tunnel, a corridor of thin interstellar gas near the far edge of the Local Bubble, the cavity the Sun is travelling through.
A blue-white 2nd-magnitude star a few degrees west of Sirius, at the Great Dog’s front leg. Its name, the Herald, comes from rising just ahead of Sirius. Its pulsing is far too slight to see, but its cool light makes a fine partner to Sirius’s glare.
When and where to see it
It is best placed in the evening sky around January, when it crosses the meridian at about 10 pm local time (around midnight in December). It can be seen from everywhere south of 72°N and never sets south of 72°S.
At its highest it stands 22° up from 50°N, 37° up from 35°N, 72° up from the equator, 73° up from 35°S.
Facts
- Type
- Star
- Constellation
- Canis Major
- Designations
- Beta Canis Majoris, β CMa, 2 CMa, HR 2294, HD 44743, HIP 30324
- Magnitude
- 2.0
- Position
- RA 6h 22.7m, Dec −17° 57′ (J2000)
- Spectral type
- B1II-III
- Colour
- blue-white (B−V -0.24)
- Distance
- 490 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Mirzam (Beta Canis Majoris) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.