Acrux

Acrux is the brightest star in the Sternbild Crux (das Kreuz des Südens) at a combined magnitude of 0.76. It is a Mehrfachsternsystem located about 320 Lichtjahre von der Erde entfernt. The two brightest components, Alpha1 Crucis (magnitude 1.33, Spektraltyp B0.5IV) and Alpha2 Crucis (magnitude 1.73, Spektraltyp B1V), are separated by about 4 Bogensekunden. Both are hot, massive blue stars. Alpha1 is itself a spektroskopischer Doppelstern, making Acrux at least a triple system.

Acrux marks the foot (southern point) of das Kreuz des Südens and is visible only from latitudes south of about 27°N. A kleines Teleskop easily splits the two main components, which present a beautiful pair of nearly matched blue-white stars — one of the finest Doppelsterns in the sky. The color contrast with the reddish Gacrux at the top of the Cross adds to the spectacle. Acrux, together with Gacrux, points roughly toward the südlicher Himmelspol. Best observed from März through Juli from südlichen Breiten.

The name Acrux is a modern contraction of 'Alpha Crucis,' coined in the 19th century. The Kreuz des Südens was known to ancient Greeks (it was visible from the Mediterranean due to Präzession) but gradually sank below their horizon over millennia. European explorers rediscovered it in the Age of Exploration. The Portuguese navigator João Faras made the first known European observation of the Cross in 1500.