A guide to star Zubenelgenubi

All you need to know about Libra's leading star.

The lunar occultation of the double star Zubenelgenubi (Alpha-1 (α1) and Alpha-2 (α2) Librae) on the morning of 26 January. Times are correct for the UK’s centre and will vary with location. Credit: Pete Lawrence
Published: January 26, 2022 at 10:27 am
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Take a look at the modest constellation of Libra, the Scales. It isn’t particularly outstanding in terms of bright stars, but it does have a few of the best star names in the entire starry realm.

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The leading star of Libra is no exception to these rules. It's not bright, but its name is fantastic: Zubenelgenubi.

With 13 letters and six syllables, it’s a bit of a tongue-twister.

Use Scorpius and Libra to help you find stars Zubenelgenubi a and Zubeneschamali. Credit: Stellarium
Use Scorpius and Libra to help you find Zubenelgenubi. Credit: Stellarium

Zubenelgenubi is actually a double star containing the components α¹ Librae and α² Librae, which are mag. +5.1 and mag. +2.8, respectively.

It’s a binary star, with the two stars in orbit around each other. They lie at the same distance of 77 lightyears away from Earth and both have similar velocity and direction in space.

As a consequence, they are very likely to be a physical pair.

According to a 2016 decision by the International Astronomical Union, these days the name 'Zubenelgenubi' refers specifically to the brighter component, Alpha-2.

What does Zubenelgenubi mean?

Like many stars, the name Zubenelgenubi was created during the major Arabic influences on astronomy, around 1,000 years ago (for more on this, read our guide to Arabian astronomy).

Translated, Zubenelgenubi means ‘the southern claw of the Scorpion’, which harks back to the time when Libra was not a separate constellation but the front part of the constellation of Scorpius, the Scorpion.

Zubenelgenubi lunar occultations

As seen from Earth, Zubenelgenubi sits just above the ecliptic in the sky so can often be found near the Moon in a wonderful conjunction, or even being occulted by the Moon.

One such occultation occurred on 26 January 2022, when the 42%-lit waning crescent Moon passed in front of Zubenelgenubi in the early hours.

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This article originally appeared in the June 2009 issue of BBC Sky at Night Magazine.

Authors

Astronomy writer Anton Vamplew
Anton VamplewAstronomy communicator

Anton Vamplew is an amateur astronomer, author and lecturer.

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