How to find it

Zubeneschamali (Beta Librae), the brightest star in the constellation Libra the Scales, is just a touch brighter than its counterpart in Libra, the star Zubenelgenubi (Alpha Librae). Nonetheless, Zubenelgenubi wins the alpha designation, probably because it sits on the ecliptic – the annual pathway of the sun in front of the background stars. The sun passes in front of Libra from about November 1 to November 22, and the sun has its annual conjunction with Zubenelgenubi or or near November 7.

Is Zubeneschamali green with envy about Zubenelgenubi’s alpha status? Perhaps. The incomparable Burnham’s Celestial Handbook quotes the star enthusiast Willian Tyler Olcott, who refers to this star as “the only naked-eye star that is green in color.” A number of other people agree. If, indeed, Zubeneschamali is truly green or pale emerald green, it has distinguished itself from every, or almost every visible star in the starry firmament.

Check out Zubeneschamali for yourself on some summer evening, when this star shines high in your southern sky and is easy to find. Look for Zubeneschamali a good two fist-widths to the northwest (upper right) of the brilliant ruddy star Antares. Hold your fist an arm length away.) If the star doesn’t look green to the unaided eye, try binoculars. Have your friends look at this star too, and you may discover the subjective variation in color perception.

History and Myth

Both the name Zubeneschamali and Zubenelgenubi are Arabic phrases meaning “the Northern Claw (of the Scorpion)” and “the Southern Claw (of the Scorpion),” respectively. Many thousands of years ago in ancient Babylon, these two stars once belonged to the constellation Scorpius the Scorpion, and once depicted the Scorpion’s outstretched claws.

Apparently, the ancient Greeks and Romans redrew the boundaries, creating the constellation Libra the Scales. Well over 2,000 years ago, the sun on the autumn equinox shone in front of Libra, the balance symbolizing the equal duration of day and night on the equinox. At present, the sun is in front of the constellation Virgo on the autumn equinox, which falls annually on or near September 22.

In the star lore of the ancient Greeks, the constellation Virgo represents Astrea, the goddess of justice, holding Libra the Scales and weighing judgment upon human souls. It’s thought that Roman citizens associated Libra with Augustus, the dispenser of divine judgment.

Science

Science has helped Zubeneschamali to one-up its biggest rival in Libra, the alpha star Zubenelgenubi. Astronomers have determined that Libra’s beta star is considerably brighter intrinsically than its rival Zubenelgenubi. Although these two Libra stars appear nearly the same brightness as seen from Earth, that’s because Zubenelgenubi lies at less than half Zubeneschamali’s distance. Zubenelgenubi is 77 light-years away, whereas it’s 160 light-years to Zubeneschamali. Zubeneschamali’s intrinsic luminosity is nearly 5 times that of Zubenelgenubi and 130 times that of the sun.

Zubeneschamali’s position: RA: 15h 17.5m, dec: -9° 25′