What kind of star is Acrux?
Acrux, catalogued as Alpha Crucis (α Cru; name applies to component Aa), appears in the official constellation Crux. Its apparent visual magnitude is about 0.76 combined, while its estimated distance is approximately 320 light-years. Astronomers classify the object as B0.5 IV + B1 V. 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.
The coordinate pair RA 12h 26m 35.9s, Dec −63° 05′ 57″ 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.
The name Acrux
A modern contraction of “Alpha Crucis” that entered common use in the nineteenth and twentieth centuries.
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 Acrux
Identify compact Crux beside Alpha and Beta Centauri. Acrux is the brilliant southern end of the Cross. Around 75–100× magnification can separate its close blue-white visual components under steady seeing.
Deep 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.
Interesting facts about Acrux
- Acrux is the brightest system in Crux and the southernmost first-magnitude star.
- Crux and the Southern Pointers can be used to estimate the south celestial pole.
- Acrux appears single to the eye but separates into bright blue-white components in a telescope.
- Its wider visual components are separated by only about four arcseconds.
- It anchors the foot of the familiar four-star Southern Cross.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values.