When is the best time to observe Zuben Elgenubi?

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

Where is Zuben Elgenubi located in the sky?

Zuben Elgenubi lies in the constellation Libra at right ascension 14h 51m and declination -16° 03′.

What telescope do I need to split Zuben Elgenubi?

Splitting Zuben Elgenubi requires an aperture of roughly 60 mm or larger — the components are separated by about 230.8″ at magnitudes near 2.8. Larger apertures and steady seeing help resolve the pair cleanly.

Zuben Elgenubi — Double Star in Libra

HIP 72622; Alpha2 Librae; 9 Librae

Observable Double Star Good (43/100)

Sep: 230.8", Companion: mag 5.2

Magnitude 2.8^m DoubleStar Libra (Lib) Visible

Star Map + List + Plan

About Zuben Elgenubi

Description

Zuben Elgenubi is a wide double star system at magnitude 2.75 in Libra, the second brightest star in the constellation. A white subgiant of spectral type A3IV, located about 77 light-years from Earth. A telescope reveals a fainter companion (magnitude 5.2) about 231 arcseconds away, making it one of the widest bright double stars in the sky.

Observing Tips

Zuben Elgenubi is the more southerly of Libra's two main stars, forming the southern pan of the Scales with Zuben Elschemali to the north. The wide companion is visible in binoculars. The pair lies between Virgo and Scorpius on the ecliptic. Best observed May through July.

History

The name Zuben Elgenubi comes from the Arabic 'al-zuban al-janubi,' meaning 'the southern claw,' from when Libra's stars were considered part of Scorpius. The Romans separated them into Libra, the only zodiacal constellation representing an inanimate object.

Fun Facts

The ecliptic passes very close to Zuben Elgenubi, making it one of the most frequently occulted bright stars. The Moon and planets regularly pass over it, and it has been used to study the lunar limb profile during occultations.

Observe

1Physical Properties

Magnitude 2.75

Spectral Type A3 III/V giant

Star Color White (B-V 0.15)

Distance 76 ly

2Position & Identifiers

RA 14h 50m 52.7s

Dec -16° 02' 30.0"

Constellation Libra (Lib)

HR 5531

HIP 72622

HD 130841

SAO 158840

Bayer Alpha2

Flamsteed 9 Lib

SIMBAD Wikipedia

3How easy to split?

Primary 2.8 mag Companion 5.2 mag Separation 230.8″

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
150 mm Newton 150mm Newt.	Easy	Easy	Easy
Celestron C8 (203 mm SCT) C8 203mm	Easy	Easy	Easy

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

Set a location in User Settings to see visibility data.

Best season Mar – May (peak: Apr)

5Multiple Star System Triple C,E: optical

Components 3 (triple)

Component IDs O

Separation 230.8″

Companion Mag 5.2

Companion Sp F4IV

Position Angle 314°

Star Colors A: White B: Yellow-white

Discoverer SHJ 186

Notes

CPM with HR 5530. Suspected occultation double.

Separation over time

Measured 1836 → 2016 (180 y)

Separation drift 229.0" → 230.8" (+1.80")

Rate +0.0100" / y

PA drift 314° → 314° (+0°, +0.000°/y)

Slow change over generations — observable in lifetime comparisons.

Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.