Acrux is the twelfth brightest star in the sky, the southernmost first magnitude star, and the brightest and southernmost star in Crux. In fact, Acrux is a multiple star system.

 

A moderate telescope shows two similar B stars separated by 4 arcseconds. Alpha¹ is a B subgiant (visual magnitude 1.4, luminosity 25,000 times that of the Sun, surface temperature 28,000 K). Alpha², a B dwarf (visual magnitude 2.09, luminosity 16,000 times that of the Sun, temperature 26,000 K).

 

Alpha² is a 13-solar-mass single star but Alpha¹ is a spectroscopic binary whose 14- and 10-solar-mass components are separated by about one astronomical unit (AU) and complete an orbit every 76 days. Alpha¹ and Alpha², with a minimum separation of 430 AU, take at least 1,500 years to circle around each other. Another B subgiant lies 90" away from the triplet but, despite its similar velocity through space, is probably a more distant star that happens to lie along the same line of sight.

 

visual magnitude	0.77 (combined), 1.40/2.09
absolute magnitude	-4.19/-3.79
spectral type	B0.5IV + B1V
distance	320 light-years (98 pc)
position	RA 12h 26m 35.9s, Dec -63° 05' 57"
other designations	HR 4730/4731, CD -62° 2745, HD 108248/108249, SAO 251904, FK5 462, HIP 60718.