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| Brightest Stars on Jun 05, 2014

Zubenelgenubi is Libra’s alpha star

Zubenelgenubi is an Arabic name that means this star was once seen as the Southern Claw of Scorpius the Scorpion.

Use binoculars to peer at Zubenelgenubi – otherwise known as Alpha Librae – and you’ll see that it’s a double star. Astronomers have studied the motions of Zubenelgenubi’s two stars, thinking that it’s probably a binary – two physically related stars orbiting a common center of mass. However, the rather wide separation between these two stars must mean a long orbital period of perhaps 200,000 years. That suggests these two stars may not be bound by gravity, after all. Zubenelgenubi is more intrinsically luminous than our sun. It resides some 77 light-years away. Follow the links below to learn more about this fascinating star, Alpha Librae, or Zubenelgenubi!

How to see Zubenelgenubi

Saturn near Zubenelgenubi in 2014

History and mythology of Zubenelgenubi

Zubenelgenubi looks like one star to the eye, but it's actually two stars.   Image via AAO/STScI/WikiSky

Zubenelgenubi looks like one star to the eye, but it’s actually two stars. Image via AAO/STScI/WikiSky

 Zubenelgenubi is a bit fainter than the other bright star in Libra, Zubeneschamali.  It might have received the Alpha designation because it's closer to the ecliptic.

Zubenelgenubi is a bit fainter than the other bright star in Libra, Zubeneschamali. It might have received the Alpha designation because it’s closer to the ecliptic.

How to see Zubenelgenubi. Shortly after Halloween each year, Zubenelgenubi rises and sets with the sun, and can’t be seen at all. Annually, the sun and this star are in conjunction on or near November 7.

Half a year later, by early May of each year when this star stands opposite the sun in Earth’s sky, the best time to view Zubenelgenubi has arrived. Shortly after May Day, Zubenelgenubi rises around sunset, stays up all night, then sets around sunrise. In early May, this star transits – soars to its highest spot in the southern sky – around midnight for all observers around the globe (1 a.m. daylight saving time). Because this star (and all stars) returns to the same spot in the sky 4 minutes earlier daily (or 2 hours earlier monthly), Zubenelgenubi transits due south around 10 p.m. (11 p.m. Daylight Saving Time) in early June, and earlier still in July and August.

That’s why Northern Hemisphere summer (or Southern Hemisphere winter) evenings present a good time for viewing this star. During these months, it’s high up at a convenient time of night. Zubenelgenubi, though a rather faint star, is easily visible in a dark country sky. It is fairly easy to locate near its fellow star in Libra, Zubeneschamali.

This year, in 2014, the constellation Libra houses a golden light that’s even brighter than Libra’s two brightest stars. It’s the ringed planet Saturn, which is easy to see with the unaided eye and whose rings are easily viewed in a backyard telescope.

Zubenelgenubi is a touch fainter than Zubeneschamali. Nonetheless, Zubenelgenubi enjoys the alpha designation in the constellation Libra the Scales, probably because of its proximity to the ecliptic – the path of the sun, moon and planets in our sky.

The planet Saturn shines in front of the constellation Libra in 2014, outshining Libra's two brightest stars, Zubenelgenubi and Zubeneschamali. Libra? Here's your constellation

The planet Saturn shines in front of the constellation Libra in 2014, outshining Libra’s two brightest stars, Zubenelgenubi and Zubeneschamali. Libra? Here’s your constellation

In any year, you can find the constellation Libra between the stars Antares and Spica. But in 2014, the planet Saturn acts as your guide to this fairly faint constellation.

In any year, you can find the constellation Libra between the stars Antares and Spica. But in 2014, the planet Saturn acts as your guide to this fairly faint constellation.

Zubenelgenubi sits midway between two brilliant stars in other constellations. It’s between Antares in the constellation Scorpius and Spica of the constellation Virgo. Zubenelgenubi shines to the west (right) of ruddy Antares, and to the east (left) of blue-white Spica.

The constellation Libra from Urania’s Mirror, a boxed set of 32 constellation cards first published in or before 1825.  Via ianridpath.com

The constellation Libra from Urania’s Mirror, a boxed set of 32 constellation cards first published in or before 1825. Via ianridpath.com

History and mythology of Zubenelgenubi. The names of Libra’s two brightest stars are derived from Arabic. Zubenelgenubi means “the Southern Claw (of the Scorpion)” and Zubeneschamali means the “the Northern Claw.” These names hark back to the times of the ancient Babylonians, who saw these Libra stars as part of the constellation Scorpius the Scorpion.

Apparently, the Greeks and Romans separated this part of Scorpius into the constellation Libra the Scales, because the sun shone in front of this constellation on the autumn equinox. The balance symbolizes the equal lengths of the day and night that come with the equinox. Libra marked the position of the autumn equinox well over 2,000 years ago. At present, the sun shines in front of the constellation Virgo on the autumn equinox.

According the Greek mythology, Virgo represents Astrea, the goddess of justice, holding Libra the Scales. Richard Hinkley Allen, in his classic work Star Names, says Libra in Roman eyes may have been the deification of Augustus as the arbiter of justice.

Zubenelgenubi’s position is at RA: 14h 51.4m, dec: -16° 5′