How to find it
Zubeneschamali, aka Beta Librae, is the brightest star in the constellation Libra the Scales. It’s a star you can find on Northern Hemisphere summer evenings. It’s just a touch brighter than the other bright star in Libra, called Zubenelgenubi. But, in the constellation Libra, Zubenelgenubi is designated as the alpha star.
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.
By the way, if Zubeneschamali is brighter, why isn’t it the alpha star of its constellation? It might be because Zubenelgenubi sits on the ecliptic – the annual pathway of the sun in front of the background stars.
Check out Zubeneschamali for yourself on some summer evening. Assuming you’re in the Northern Hemisphere, this star shines high in your southern sky each summer and is easy to find.
Look for Zubeneschamali a good two fist-widths to the northwest (upper right) of the brilliant ruddy star Antares in the constellation Scopius – one of the only constellations that looks like the creature for which it was named. 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. You might discover that people see colors differently!
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 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.
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.
Zubeneschamali’s position: RA: 15h 17.5m, dec: -9° 25′