Beta Scorpii the sixth-brightest star in the constellation Scorpius, but has a prominent position in the Scorpion's claws. β Sco also has the traditional names Acrab, meaning "Scorpion" in Arabic, and Graffias, meaning "claws", a name it shares with ξ Sco. Because it is close to the ecliptic, β Sco can be occulted by the Moon and, very rarely, by planets. The last occultation by took place on 13 May 1971, by Jupiter's moon Io, and provided much of what we know about the system.
β Sco is a double star with a separation of 14" between its magnitude 2.56 and 4.90 components. At a distance of 530 light years, this makes them about 2200 AU apart; they take over 16,000 years to orbit each other. The brighter component has over 20,000 times the Sun's luminosity. They are both hot, class B0.5 V and B2 V class stars at least 10 times as massive as our own Sun; both stars are expected to end their evolution as supernova explosions.
β1 Sco, the brighter of the pair, has another 10th magnitude companion 0.5", or about 80 AU, distant. It is very difficult to split, even with large amateur telescopes. Furthermore, both β1 Scorpii and β2 Scorpii are themselves spectroscopic binaries, bringing the total number of stars in the system to five. The spectrum of β1 Sco shows two stars in orbit with a period of 6.8 days, separated by merely 0.001", or 0.3 AU.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]