What kind of star is Mimosa?
Mimosa, catalogued as Beta Crucis (β Cru; name applies to component Aa), appears in the official constellation Crux. Its apparent visual magnitude is about 1.23–1.31, while its estimated distance is approximately 280 light-years. Astronomers classify the object as B0.5 III primary; multiple system. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Beta Crucis is a multiple early-B system dominated by a Beta Cephei pulsator. Its short-period pressure modes and longer-period gravity modes penetrate different layers, allowing asteroseismology to constrain interior rotation and mixing. The main star belongs to an eccentric spectroscopic binary, and the IAU name Mimosa applies specifically to component Aa. Chandra spectra show comparatively soft, stable X-rays consistent with shocks distributed through the massive star's wind rather than a solar-type corona. Those observations also identified a nearby X-ray-bright pre-main-sequence star that is probably a physical low-mass companion. Measurements referring simply to “Mimosa” can therefore mix several physical sources unless the instrument's angular resolution and component label are stated.
The coordinate pair RA 12h 47m 43.27s, Dec −59° 41′ 19.6″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Mimosa data at a glance
| Proper name | Mimosa | Catalogue designation | Beta Crucis (β Cru; name applies to component Aa) |
|---|---|---|---|
| Constellation | Crux | Apparent magnitude | about 1.23–1.31 |
| Spectral or system type | B0.5 III primary; multiple system | Estimated distance | approximately 280 light-years |
| Right ascension (J2000) | 12h 47m 43.27s | Declination (J2000) | −59° 41′ 19.6″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Mimosa
The origin of Mimosa is uncertain; Becrux, a contraction of Beta Crucis, is a historical alternative. The IAU name applies specifically to β Crucis Aa.
Mimosa's etymology remains uncertain, while Becrux is a transparent modern contraction of Beta and Crux. The star's place in the Southern Cross made it prominent in navigation and in national emblems, including the flags of Australia, New Zealand and Papua New Guinea. Those political symbols are comparatively recent; Indigenous peoples across the Southern Hemisphere maintain older and distinct interpretations of the same sky region that should not be treated as variants of the European cross.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Mimosa
Locate compact Crux beside the Southern Pointers. Mimosa is the bright blue-white star on the Cross’s eastern arm. Its variability is too slight for casual naked-eye detection.
Southern sky; circumpolar across much of the Southern Hemisphere and invisible from most of Europe. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Observe during March through June evenings when Crux is high in southern skies.
- Identify Mimosa as the eastern arm, not the lower star Acrux or red upper star Gacrux.
- Compare its blue-white colour with Gacrux in the same binocular field.
- Its pulsations and close spectroscopic companion are not separable by eye; they require precision time-series measurements.
Interesting facts about Mimosa
- Mimosa is the second-brightest star in Crux after Acrux.
- It is a multiple blue-white star system.
- The primary is a Beta Cephei variable with small, rapid pulsations.
- Its oscillations make it valuable for asteroseismology, which probes stellar interiors.
- Mimosa forms the eastern arm of the Southern Cross.
Continue from Mimosa into the night sky
Use the Crux constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.