The southern centaur holds our nearest stellar neighbours and a diamond star
Centaurus packs in 281 stars visible without a telescope, more than any other constellation. Among them is Alpha Centauri, the closest star system to the Sun, and a white dwarf whose carbon may have crystallised, earning it the nickname Lucy after a Beatles song about diamonds in the sky.
Sprawling across the southern sky, Centaurus depicts the half-man, half-horse creature of Greek myth and was among Ptolemy's 48 constellations in the 2nd century. It remains one of the 88 in use today. Oddly for so bright a region, the Milky Way lies outside its borders. Its two leading stars act as southern pointers that guide observers to Crux, the Southern Cross.
Alpha Centauri, also called Rigil Kentaurus, meaning foot of the centaur, or Toliman, two male ostriches, is really three stars 4.4 light-years off. Two yellowish suns orbit each other every 80 years and will look closest through telescopes in 2037 and 2038; to the naked eye they merge into the sky's third-brightest point of light. The third member, Proxima, is a faint red dwarf nearly 2 degrees away that takes about a million years per orbit and flares by more than a magnitude in bursts lasting minutes. Alpha moves quickly across the sky and in roughly 4000 years will sit just half a degree from Beta Centauri, a blue giant about 525 light-years away.
Other residents are just as striking. HR 5171 is among the largest stars ever found. R Centauri, a Mira-type variable some 1,250 light-years away, swings between magnitudes 5.3 and 11.8 over 18 months. Around the young star PDS 70, astronomers in July 2018 obtained the first conclusive picture of a planet forming inside a disc of dust and gas. Menkent, an orange giant, is the only bright member easily seen from mid-northern latitudes.
Then there is Omega Centauri. Ancient observers took it for a single star, but Edmond Halley recognised it as something else in 1677, and James Dunlop identified it as a globular cluster in 1827. It sits 17,000 light-years away, spans 150 light-years, looks as wide as the full Moon, and outshines a million suns. Its several million stars average 12 billion years old, fuelling suspicion that it is the leftover heart of a dwarf galaxy swallowed by our own.
Source: Centaurus
