About Alpha Cru
Description
Alpha Crucis B is the fainter component of the Acrux double star system at magnitude 1.73, a blue main-sequence star of spectral type B1V. Together with the brighter A component, it forms one of the finest visual double stars in the southern sky. The B component has a luminosity of about 16,000 times solar.
Observing Tips
Resolved in a small telescope at moderate magnification as the fainter companion to Acrux A, separated by about 4 arcseconds. The pair appears as two brilliant blue-white points, nearly equal in brightness. This is one of the most rewarding double stars accessible from the southern hemisphere. Best observed March through June.
History
The double nature of Acrux was first noted by Jesuit missionary Jean Richaud while observing a comet from Pondicherry, India in 1685. It was one of the first double stars discovered in the southern sky and remains one of the showpiece objects for southern hemisphere observers.
Fun Facts
The two components of Acrux are among the nearest pair of B-type giants to Earth that can be resolved visually. The system may actually contain additional components, making it a quadruple or even quintuple star system.
Observe
1Physical Properties
2Position & Identifiers
3How easy to spot?
| Equipment | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| Naked eye Naked eye | Easy | Easy | Easy |
| 50 mm finder 50mm finder | Easy | Easy | Easy |
| 150 mm telescope 150mm scope | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Survey Image
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Explore
7
Size Comparison
8
Compare Stars
9
Spectral Classification
10
Hertzsprung-Russell Diagram
11
Stellar Lifecycle
12
Blackbody Spectrum
13
Stellar Absorption Spectrum
Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.
14
Stellar Fusion
Discover
15Stellar Notes
16
Light Travel Time Machine
17
Relativistic Travel
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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