Agena

Agena (also known as Hadar) is the second brightest star in Centaurus and the 11th brightest in the night sky at magnitude 0.61. It is a giant star of spectral type B1III located about 390 light-years from Earth. Agena is actually a triple star system: the primary is a spectroscopic binary of two blue giant stars orbiting each other every 357 days, with a more distant third companion. The system's combined luminosity is about 41,000 times that of the Sun.

Agena is a Southern Hemisphere object, visible only from latitudes south of about 30°N. Together with Alpha Centauri, it forms the 'Southern Pointers' — the two bright stars that point toward the Southern Cross (Crux), a vital navigation aid in the southern sky. The two stars are about 4.5 degrees apart and make a striking pair. Best observed from March through September from southern latitudes.

The name Hadar comes from the Arabic for 'ground' or 'soil,' possibly referring to its low position as seen from Arabian latitudes. The alternative name Agena is Latin, possibly meaning 'the knee.' Along with Alpha Centauri, it has been used by Polynesian and Aboriginal Australian navigators for centuries. Its spectroscopic binary nature was discovered in the early 20th century.