Zubeneschamali (Beta Librae)
Zubeneschamali (Beta Librae) is a star in the constellation Libra, magnitude 2.6.
The Scorpion’s northern claw — long described as the only green star seen by the naked eye.
Is it green? Earlier generations of observers described Zubeneschamali as the only naked-eye star with a greenish tint. Most modern eyes see white or bluish, as you would expect of a hot B-type star, and there is no accepted explanation for the green.
Its brightness may have changed too. Eratosthenes found it brighter than Antares; Ptolemy, some 350 years later, called the two equal. Perhaps Antares brightened, or perhaps this star varies — today it changes by only a few hundredths of a magnitude.
The star is about 4.8 times the Sun’s width and 410 times as luminous, with a surface near 12,000 K, and it spins more than 100 times faster than the Sun. Its name is Arabic for “the northern claw”, from the days when Libra was seen as the claws of the Scorpion.
Zubeneschamali (Beta Librae) is 190 light-years away: the light we see from it set off around 1835, 10 years before Neptune was discovered.
Did you know?
- A clear window. Its hot surface gives a simple, clean spectrum, which makes it ideal for studying the thin gas and dust that lie between the star and us.
- The northern pan. It was also known as Kiffa Borealis, from the Arabic for “the northern pan” of the scales, and in Latin as Lanx Borealis.
- A future giant. In about 200 million years it will run out of hydrogen in its core and become a giant much like Kornephoros, Beta Herculis, which started out with a similar mass.
A blue-white star of magnitude 2.6, the brightest in Libra. Some observers have called it faintly green — judge for yourself by comparing it with Zubenelgenubi, about 9 degrees to the south-west, and with orange Antares.
When and where to see it
It is best placed in the evening sky around June, when it crosses the meridian at about 10 pm local time (around midnight in May). It can be seen from everywhere south of 81°N and never sets south of 81°S.
At its highest it stands 31° up from 50°N, 46° up from 35°N, 81° up from the equator, 64° up from 35°S.
Facts
- Type
- Star
- Constellation
- Libra
- Designations
- Beta Librae, β Lib, 27 Lib, HR 5685, HD 135742, HIP 74785
- Magnitude
- 2.6
- Position
- RA 15h 17.0m, Dec −9° 23′ (J2000)
- Spectral type
- B8Vn
- Colour
- blue-white (B−V -0.11)
- Distance
- 190 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Zubeneschamali (Beta Librae) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.