Libra: The Scales (The Balance)

Look up the names of Libra's two main stars and something strange jumps out immediately. Zubeneschamali means "the northern claw." Zubenelgenubi means "the southern claw." A constellation supposedly about a balance is named, star by star, after a crab or scorpion's pincers. That is not an accident, and it tells you something true about how this part of the sky actually got its shape.

The only object in the zodiac that isn't a creature

Libra is the one zodiac constellation that represents a thing rather than a person or an animal. Its brightest star is Zubeneschamali, a blue-white star at magnitude 2.61 — worth noting because it is the Beta star, not the Alpha, a reminder that the Greek letter assigned to a star does not always track its actual brightness. The Alpha star, Zubenelgenubi, comes in at magnitude 2.75 and is itself a wide double star, splittable with nothing more than sharp eyes. A third star, Brachium, is a red giant at magnitude 3.29 that was at one point assigned to the neighboring constellation Scorpius rather than to Libra. Libra's best month is June.

Claws first, then a balance

The Greeks originally saw this region as an extension of the Scorpion next door, its claws reaching out into the space Libra now occupies. That earlier identity is exactly why the star names still say "claw" today, even though nobody pictures a scorpion here anymore. It was the Romans who separated this patch of sky into its own figure, the Scales, and attached it to Astraea, the goddess of justice, weighing right against wrong.

The idea of a balance here is actually older than the Romans, though. Mesopotamian astronomers had already mapped a set of scales onto this stretch of sky, called MUL Zibanitu, long before Rome existed. The Roman version did not invent the scales. It formalized something the Babylonians had already been drawing for a very long time.

Not much to see, but worth the look

Libra is not a constellation people visit for a rich deep-sky object. It holds one notable entry, NGC 5897, a loose and fairly faint globular cluster. It is not going to compete with the showpieces in nearby Scorpius or Sagittarius, but if you have already found Libra's stars, it is there for anyone with a telescope who wants to push a bit further.

Two names, two very different things in the sky

Libra the constellation is the actual pattern of stars described above, claws and scales and all, with fixed boundaries on the sky. Libra the zodiac sign is a completely separate object: a thirty-degree division of the tropical zodiac tied to the calendar, not to these specific stars. The two used to sit closer together than they do now. Over thousands of years, precession has pulled the constellations backward relative to the tropical zodiac's fixed seasonal markers, and Libra is no exception. The mechanism behind that drift is covered properly in our piece on precession, and if the astrological sign is what actually brought you here, it has its own page.

What this means for you tonight

If Libra is a placement in your chart, that is the tropical sign, not this specific group of stars, and the two will not literally line up if you go looking. Go looking anyway. In June, scan the southern sky for two moderately bright points close together, roughly matched in brightness — that pairing is Zubeneschamali and Zubenelgenubi. Try to notice, standing there, that the brighter of the two carries the "Beta" designation rather than "Alpha." It is a small, concrete way to see for yourself that star names were assigned by older conventions, not strictly by rank, and it is a fact worth having in your pocket before you look at any other constellation's star list. For how that Greek-letter naming system works in general, read how star brightness works, and for the basics of constellation boundaries, see what a constellation is.