Space & the universe

This constellation spent 200 years as a bee before it was a fly

Musca is a small, faint constellation tucked into the deep southern sky near the Southern Cross, representing a fly—oddly, the only official constellation to depict an insect. It was one of twelve new southern constellations devised by Petrus Plancius from star observations made by two Dutch navigators on a late-16th-century trading voyage, and it first appeared on a celestial globe around 1597-98 before showing up in a printed star atlas in 1603. For about two centuries it was instead called Apis, the Bee, before the French astronomer Lacaille settled on Musca in the mid-1700s, briefly adding "Australis" to distinguish it from a now-discarded northern fly constellation. Various peoples read their own pictures into its stars too, from a ceremonial boomerang and headband among Australia's Wardaman to figures tied to neighbouring constellations among South America's Kalapalo. Today it sits quietly among the smaller constellations, ranked near the bottom for size and visible only from southern and tropical latitudes.

Its handful of modestly bright stars tell a more eventful story than their faintness suggests. Several of them, including the leading stars Alpha and Beta, belong to a loose stream of young, hot blue-white stars called the Scorpius-Centaurus association that drifts together through the galaxy, while others, like the red giant Epsilon, merely happen to lie nearby without sharing that common motion. The constellation hosts pulsating variable stars, eclipsing binaries, and two Cepheids used as cosmic distance markers, plus the triple system Theta Muscae, whose rare Wolf-Rayet star and massive companions together outshine the Sun by over a million times. More dramatic still are its stellar corpses and explosive binaries: a nova that erupted in 1983 and was the first ever detected in X-rays, a black hole paired with an ordinary star that flared in 1991, a neutron star locked with a low-mass companion, and a symbiotic pair of a red giant feeding a white dwarf without producing fireworks. Three of its stars have also been found to host planets or planet-like companions, including a massive gap in the dusty disk around the young star HD 100546 that may hide a giant planet or even a brown dwarf.

Beyond the stars, Musca holds a scattering of nebulae and clusters worth a telescope's attention. These include the oddly structured planetary nebula NGC 5189, shaped by ejections from a dying star and a hidden companion, and the tiny, colourful Engraved Hourglass Nebula, along with several other planetary nebulae of varying size and distance. Part of the dark Coalsack Nebula, famous mostly for lying in next-door Crux, spills over into Musca's territory, and the constellation has its own dark cloud, the narrow, river-like Dark Doodad Nebula, trailing from an ancient globular cluster. That cluster, along with another nearby one partly hidden by galactic dust, ranks among the oldest star groupings in the Milky Way. Altogether, the fly's small patch of sky packs in a surprising density of extreme and ancient objects for its size.

Most of Musca's brightest stars aren't a chance alignment they're members of the Scorpius Centaurus association, hot blue-white stars that appear to share a common origin and a common motion through the Milky Way.

Read the whole of Musca on Wikipedia

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