Mu Crucis is a double star in the southern constellation of Crux, which is commonly known as the Southern Cross. Its name is a Bayer designation that is Latinized from μ Crucis and abbreviated Mu Cru or μ Cru. μ Crucis is a wide pair of spectral class B stars, magnitude 4.0 and 5.2 respectively, forming the seventh-brightest star in the constellation. They lie about 370 light-years away, and both stars are likely physically attached. The brighter component is known as μ1 Crucis or μ Crucis A, while the fainter is μ2 Crucis or μ Crucis B.
μ1 Crucis is the brighter of the two stars with an apparent magnitude of 4.0. It is a hot massive main sequence or subgiant star, over a thousand times as luminous as the sun.
μ2 Crucis is the fainter of the pair. Its apparent magnitude is 5.2 and it is a Be star, a star spinning so quickly that it has ejected a disc of material that creates emission lines in its spectrum. The disc is inclined at 36° to our line of sight.
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