object. The bar of the "A" consists of a line of four stars. On the right (south) is BU Cru, a magnitude 6.92 B2 supergiant and eclipsing binary. Next to it is BV Cru, a magnitude 8.662 B0.5 giant and Beta Cephei variable. Next in line is DU Cru, an M2 red supergiant that varies irregularly between magnitude 7.1 and 7.6. The last of the four is CC Cru, a magnitude 7.83 B2 giant and ellipsoidal variable. Each leg of the base of the asterism's outline is marked by a blue supergiant star. HD 111990 (HIP 62953) is magnitude 6.77 and B1/2. The star κ Cru itself is magnitude 5.98 and B3. Physical characteristics The Jewel Box cluster is one of the youngest known open clusters. The mean radial velocity of the Jewel Box cluster is . The brightest stars in the Jewel Box cluster are supergiants, and include some of the brightest stars in the Milky Way galaxy. Calculating its distance is difficult due to the proximity of the Coalsack Nebula, which obscures some of its light. Observation The Jewel Box cluster is regarded as one of the finest objects in the southern sky. It is visible to the naked eye as a hazy object of the fourth magnitude. It can be easily located using the star Beta Crucis as a guide, and appears as a fourth magnitude object. It is impressive when viewed with binoculars or a small or large telescope. Three members along the crossbar of the A-shaped asterism lie in a straight line known as the 'traffic lights' due to their varying colours. Gallery References External links SEDS: NGC 4755, with a Copyright Anglo-Australian Observatory Image of NGC 4755 A Copyright T. Warner Amateur Image of NGC4755 Open clusters Crux (constellation) NGC objects 094b