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August's Star of the Month: Zubenelgenubi


The star Zubenelgenubi (zoo-BEN-el-je-NEW-bee) is not particularly striking at first glance. It's only the second brightest in the constellation of Libra, the scales, which itself is pretty dim. Oftentimes, just to find this star, you first have to find the bright stars Spica of the constellation Virgo, the virgin, and Antares of the constellation Scorpius, the scorpion. Zubenelgenubi, which is flanked to the west (or right) by blue-white Spica, and to the east (or left) by ruddy Antares, shines somewhat feebly between these two stars.

Nonetheless, given an unobstructed view to the southwest, you should have little trouble finding Zubenelgenubi at nightfall. Shortly after sunset, you'll see what looks like an exceedingly bright star quite low in your western sky. This is actually the planet Venus, the brightest heavenly body next to the Sun and the Moon. Look for Spica to the upper left of Venus, rather low in the southwest sky. Then look for orange-red Antares to glower just west of due south, not much higher up than Spica. As always, Zubenelgenubi sits between these two stars.

Zubenelgenubi sets around midnight at the first of the month but about ten o'clock by the month's end. On August 14, Zubenelgenubi snuggles to the lower right of the Moon, with both readily fitting into the same binocular field of view.

By the way, on August 1st Venus resides near the border of Virgo and Leo, the lion. The brilliant planet travels eastward (right to left) through Virgo all month, conjoining with Virgo's brightest star, Spica, by August 31. At nightfall at that time, Venus will be very close to the horizon, but it's not likely that you'll see Spica right next to Venus unless you use binoculars.

But back to Zubenelgenubi, which - unlike the stock market nowadays - instantly pays dividends. Simply aim your binoculars at Zubenelgenubi, and presto, you double your pleasure, seeing two stars in one! Like so many stars, Zubenelgenubi is a binary, or two stars revolving around a common center of gravity, but what makes Zubenelgenubi so very special is that this binary - unlike most - is so easy to see. If you're unaccustomed to using binoculars and easily get lost, try placing our feature star on top of a tree or some such thing. Then follow the tree up to Zubenelgenubi, viewing the dimmer star to the right of its brighter companion.

According to my source of information, Zubenelgenubi lies some 77 light years away, its two components separated by 140 times Pluto's distance from the Sun. The orbital period is an estimated 200,000 years.

If, by chance, you were born on November 7, the Sun is in conjunction with Zubenelgenubi annually on your birthday.

Stars of the Month Page

August 2002 Feature Article: The Perseids