The Moon joins Saturn, Mars, and the Scorpion’s Claws on the night of Sunday, 31 August. Looking toward the southwest after dusk on Sunday night, it will be easy to see the waxing crescent Moon form a compact, equilateral triangle with the two bright planets. But look a little further afield and find the two brightest stars in the constellation Libra, α and β Librae. These stars are known by their Arabic names “Zubenelgenubi" and "Zubeneschamali,” meaning the Southern Claw and the Northern Claw. These names refer to the ancient Greek concept of the constellation Scorpius; other ancient cultures saw them as a balance (Libra). The Bablyonians saw them as as scales sacred to the god Shamash, while the Romans thought Libra symbolized the scales held by Astraea, the goddess of justice.
Zubenelgenubi reveals itself to be a fine double star when viewed through an ordinary pair of binoculars. Zubeneschamali is less visually attractive, but may not have always been: Eratosthenes wrote that Beta Librae was brighter than Antares, the brightest star in Scorpius, in his time. Ptolemy, writing 350 years later, said it was as bright as Antares. It is unknown whether Antares became brighter or if Zubeneschamali dimmed in brightness. It appears to have been steady for the ~2,000 years since Ptolemy.
See Mars and Saturn separated by barely more than the width of the full Moon tonight in the southwestern sky after dusk. Slowly approaching each other in Earth’s night sky over the past several weeks, the Ringed and Red Planets reach minimum separation tonight in an astronomical phenomenon called an appulse. But the close approach is only an illusion: the two planets are separated in space by roughly 8 astronomical units, or about 745 million miles (1,200,000,000 km).
(Graphic credit: Astronomy Magazine)