When is the best time to observe Agena?

Agena is best observed from March through May, with peak visibility during April when it transits around midnight in the Northern Hemisphere.

Where is Agena located in the sky?

Agena lies in the constellation Centaurus at right ascension 14h 04m and declination -60° 22′.

What telescope do I need to split Agena?

Splitting Agena requires an aperture of roughly 200 mm or larger — the components are separated by about 0.2″ at magnitudes near 0.6. The companion is about 3.3 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Agena — Double Star in Centaurus

HIP 68702; Beta Centauri

Magnitude 0.6^m DoubleStar Centaurus (Cen) Visible

Star Map + List + Plan

About Agena

Description

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.

Observing Tips

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.

History

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.

Fun Facts

Despite being 100 times farther away than Alpha Centauri, Agena appears almost as bright because it is intrinsically far more luminous. The two stars serve as reliable pointers to the Southern Cross — a line drawn through them leads directly to Gacrux (Gamma Crucis) at the top of the Cross.