Les Dalrymple is a guide at Sydney Observatory and a keen observer. Below he discusses the history of an often overlooked constellation close to the Southern Cross.
With its stars too far south to be seen by classical cultures, the constellation of Musca – the fly, (along with eleven other new southern constellations) were introduced by Dutch cartographer Petrus Plancius in his star-globe of 1598. Its (unlabelled) depiction was based on star-positions catalogued by Pieter Dirkszoon Keyser and Frederick de Houtman of the Dutch East Indies Company. Plancius’ fly was copied two years later by another Dutch cartographer Jodocus Hondius on his own star-globe but was again unlabelled. Johannes Bayer adopted and copied the twelve new southern constellations from the globe by Hondius just a few years later again in his milestone star-atlas “Uranometria” of 1603, but Bayer (incorrectly) labelled the stars known today as Musca, as a bee – Apis.
Plancius produced another star globe in 1612 clearly identifying and labelling this southern group as “Muia” – from the ancient Greek for fly and further, carved some faint, unused stars out of northern Aries dubbing them “Apes” – Greek for bee. Despite the clarification, Bayer’s bee, adjoining and directly south of the Southern Cross gained popular acceptance for more than two centuries.
Meanwhile, back in the northern sky, the stars that formed the Northern Bee were renamed “Vespa” – the wasp by German astronomer Jacob Bartsch in his star atlas of 1624. Polish astronomer Johannes Hevelius altered it again in his 1690 atlas labelling it “Musca Borealis” – the Northern Fly. It remained as the northern fly until the rationalisation of the constellations undertaken by Henry Russell and Eugene Delporte on behalf of the International Astronomical Union in the 1920s and 30s when Musca Borealis was swatted, apparently forever, and its stars returned to Aries.
Returning again to the southern sky, following the exhaustive mapping and constellation making of French astronomer Nicholas de Lacaille from South Africa in the 1750s, Bayer’s bee reverted to the original form devised by Plancius of a fly – Musca Australis to distinguish it from the northern version. Upon Musca Borealis’ demise in the 1920s, Musca Australis was truncated to simple Musca – the one and only insect of the modern sky.
Musca is easy to identify even under light-polluted suburban locations. A line drawn from Delta (δ) Crucis (the fourth brightest star in the Southern Cross) through Alpha (α) (the brightest) and extended once lands you almost in the middle of the skew-whiff “five of diamonds” shape made by its five brightest stars that are all pretty evenly matched in brightness. Many of Musca’s brighter stars are actually related and form part of the Lower Centaurus-Crux subgroup of the Scorpius–Centaurus O-B association of stars – a group of predominantly hot blue-white stars that share a common origin, velocity and direction of travel around our Milky Way.
The next time you step outside this autumn to take a peek at the Southern Cross take a moment to identify Musca, our sky’s only insect.