Mimosa (Beta Crucis)
Mimosa (Beta Crucis) is a star in the constellation Crux, magnitude 1.3.
The second star of the Southern Cross — a young blue giant that may explode in a few million years.
Mimosa is a newcomer. The system is only 8 to 11 million years old, yet its main star — a blue giant 15 times the Sun’s mass — has already used up the hydrogen in its core. Heavy stars live fast: in roughly 6 million years it may explode as a supernova. Its surface, at about 27,000 K, glows blue-white, and a fierce wind streams off it at 2,000 km/s or more.
It does not live alone. A smaller star circles it every five years, too close to separate in a telescope, and a third, still-young star, announced in 2007, glows in X-rays. The giant is also a variable star, pulsing gently with three rhythms, each a little over four hours long. Its name may come from the mimosa flower, or from the Latin for ‘actor’.
Mimosa (Beta Crucis) is 280 light-years away: the light we see from it set off around 1745, 25 years before Charles Messier published his famous catalogue.
Did you know?
- On five flags. Mimosa is one of the Southern Cross stars on the flags of Australia, New Zealand, Samoa and Papua New Guinea. On Brazil’s flag it stands for the state of Rio de Janeiro.
- Once a Greek star. Precession once placed Mimosa far enough north for the ancient Greeks and Romans to see it from latitudes north of 40°. They counted it as part of Centaurus.
- A record age. Asteroseismology — reading a star’s insides from its pulsations — gives Mimosa an age of 11 million years. It is the most massive star whose age has been found this way.
A bright blue-white star at the eastern end of the Southern Cross’s crossbar, second only to Acrux in the pattern. Compare it with orange Gacrux at the top of the Cross for a vivid colour contrast.
When and where to see it
It is best placed in the evening sky around May, when it crosses the meridian at about 10 pm local time (around midnight in April). It can be seen from everywhere south of 30°N and never sets south of 30°S.
At its highest it stands below the horizon from 50°N, below the horizon from 35°N, 30° up from the equator, 65° up from 35°S.
Facts
- Type
- Star
- Constellation
- Crux
- Designations
- Beta Crucis, β Cru, HR 4853, HD 111123, HIP 62434
- Magnitude
- 1.3
- Position
- RA 12h 47.7m, Dec −59° 41′ (J2000)
- Spectral type
- B1IV
- Colour
- blue-white (B−V -0.23)
- Distance
- 280 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Mimosa (Beta Crucis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.