Musca
“The Fly” · Southern · best around May evenings
Real star positions and magnitudes (HYG database via D3-Celestial, BSD-3). Lines are the conventional stick figure; north is up.
The story
The southern fly, buzzing just below the Southern Cross — the only insect among the 88 (a bee on some old charts).
How to find it
Directly south of Crux.
✦ What lives inside it
- Dark doodad nebula (astrophotographers' favorite)
The deep dive
Researched for the Atlas from Wikipedia — Musca (15,019 characters read) · updated Sep 20, 2026
01 A Bee Before It Became a Fly
For roughly two centuries, the stars now called Musca were known by an entirely different creature. When Johann Bayer published his landmark star atlas Uranometria in 1603 — the first celestial atlas to depict the constellation — he labelled it Apis, Latin for the bee. The insect identity only shifted permanently after Nicolas Louis de Lacaille called it la Mouche (the fly) on his 1756 planisphere of the southern sky, then Latinised it as Musca Australis in 1763. The word Australis was necessary because a rival northern constellation, Musca Borealis, had been assembled from a handful of stars in Aries. Once that grouping fell out of official use, the southern fly kept only the single name Musca. Today it holds an unusual distinction: it is the only officially recognised constellation depicting an insect. An earlier, charming 1603 globe by Willem Blaeu showed the chameleon in the adjacent constellation extending its tongue as if trying to catch Musca — a small piece of astronomical storytelling that did not survive into modern maps.
02 Born From a Dutch Trading Voyage
Musca owes its existence to commerce as much as curiosity. The Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman sailed on the Eerste Schipvaart — the first Dutch trading expedition to the East Indies — and systematically recorded the southern sky invisible from European latitudes. De Houtman catalogued the constellation in 1598 under the Dutch name De Vlieghe, meaning the fly, and assigned just four stars to it: what would later be called Beta Muscae marking the head, Gamma the body, and Alpha and Delta the left and right wings. The astronomer Petrus Plancius then transformed these observations into a globe 35 centimetres in diameter, published in Amsterdam together with cartographer Jodocus Hondius around 1597 or 1598, though the constellation appeared on it without a name. Musca was one of 12 new constellations that Plancius built from Keyser and de Houtman's data, a batch of southern star figures that filled the blank regions around the south celestial pole and permanently reshaped the sky's geography.
03 Indigenous Skies: Boomerangs and Flutes
Indigenous cultures across the southern hemisphere looked at the same stars and built entirely different stories. The Wardaman people of the Northern Territory in Australia saw the main stars of Musca as a ceremonial boomerang, positioned within what they call the Central Arena — a sacred region surrounding Crux that depicts lightning creation beings and the place where Wardaman customs are taught. Within that framework, Alpha and Beta Muscae specifically represented a ceremonial headband, while Gamma and Delta were read as two armbands. Far to the northeast, the Kalapalo people of Mato Grosso state in Brazil grouped Alpha and Beta Muscae together with Beta and Kappa Crucis under the name Kutsu anangagï, meaning Ornate Hawk-Eagle's double flutes. In central Australia, the Arrernte and Luritja peoples divided the sky along the Milky Way: stars to the east belonged to Arrernte camps, stars to the west to Luritja camps. The stars of Musca fell to the Arrernte, grouped alongside Fomalhaut, Alpha Pavonis, and Alpha and Beta Gruis.
04 A Neighbourhood of Sibling Stars Deeper
A striking proportion of Musca's brightest stars are not neighbours by chance — they are genuine relatives. Alpha, Beta, Gamma, Zeta2, and probably Eta Muscae all belong to the Lower Centaurus Crux subgroup of the Scorpius–Centaurus association, a loose extended family of hot blue-white stars that formed together and still drift in the same direction across the Milky Way. HD 103079 is also a member. These stars share a common origin, which is why so many of them cluster in the same spectral types: Alpha is B2IV-V, Beta's pair are B2V and B3V, and Gamma is B5V. Epsilon Muscae provides a useful contrast: although it sits at a similar distance of around 302 light-years, it is moving at roughly 100 kilometres per second — far faster than the association members — and does not share their origin. HD 100546, a young Herbig Ae/Be star of spectral type B9V located about 320 light-years away, is yet another Lower Centaurus Crux member, though one that has not yet settled onto the main sequence. The association effectively turns Musca into a showcase of stellar evolution across a single age cohort.
05 Theta Muscae: A Three-Star Powerhouse Deeper
Theta Muscae is one of the most extreme stellar systems in any small constellation. At an estimated 7,500 light-years from Earth, it contains three very massive, very luminous stars. At its heart is a spectroscopic binary in which a Wolf–Rayet star of spectral type WC5 or WC6 and an O-type main-sequence star of spectral type O6 or O7 orbit each other every 19 days. If the distance estimate is correct, they are only about 0.5 astronomical units apart — closer than Mercury orbits the Sun. Standing off from this tight pair at about 46 milliarcseconds is a blue supergiant of spectral type O9.5/B0Iab, separated from the inner binary by roughly 100 astronomical units. Combined, all three stars are estimated to produce over one million times the luminosity of the Sun. Wolf–Rayet stars are among the most evolved massive stars known, having shed their outer hydrogen layers and exposing their hot, nuclear-burning cores; the WC classification specifically indicates a carbon-rich stellar wind. Theta Muscae offers a rare chance to study a Wolf–Rayet object in the gravitational company of two additional massive companions.
06 Cepheids, Novas, and a Neighbourhood Black Hole Deeper
Musca hosts a remarkable concentration of exotic variable and compact objects. R Muscae and S Muscae are both classical Cepheid variables — pulsating yellow-white supergiants used as cosmic distance markers. R Muscae ranges from magnitude 5.93 to 6.73 over 7.5 days and lies about 2,037 light-years away, while S Muscae cycles between magnitudes 5.89 and 6.49 over 9.66 days and carries a hot blue-white companion thought to be one of the hottest and brightest companions of any known Cepheid. GQ Muscae, also called Nova Muscae 1983, is a white dwarf pulling material from a companion about 10 percent as massive as the Sun; the pair orbit each other every 1.4 hours, and when enough mass accumulates the system erupts. When it was discovered on 18 January 1983 at magnitude 7.1, it became the first nova from which X-rays were detected. Nova Muscae 1991 — formally GRS 1124-683 — is even more dramatic: an orange main-sequence star of spectral type K3V–K4V locked in orbit with a black hole of roughly six solar masses. Its 1991 outburst produced radiation through positron annihilation. More recently, V415 Muscae underwent a nova outburst on 8 June 2022, reaching apparent magnitude 8.7.
07 A Protoplanetary Disk Caught Mid-Formation Deeper
HD 100546, located about 320 light-years away, is the closest known Herbig Ae/Be star to Earth and one of the most studied sites of ongoing planet formation. It is a young blue-white star of spectral type B9V that has not yet settled onto the main sequence, and it is wrapped in a circumstellar debris disk that extends from 0.2 to 4 astronomical units, then resumes from 13 AU out to several hundred AU. The gap between 4 and 13 AU is particularly revealing: its shape suggests a large planet approximately 20 times the mass of Jupiter is carving the space clear. However, closer analysis of the disk profile raises the possibility that the gap-maker is a brown dwarf or even multiple planets rather than a single object. Beyond the gap, at around 47 AU, there is evidence of a protoplanet currently forming within the outer disk. HD 100546 is also a member of the Lower Centaurus Crux subgroup, meaning it formed alongside many of Musca's other bright stars — making it a window into the early conditions from which that whole stellar association emerged.
08 Planetary Nebulas: Hourglasses and Complexity
Musca contains several planetary nebulas worth knowing. The most visually distinctive is the Engraved Hourglass Nebula, catalogued as MyCn 18, sitting about 2.4 degrees east of Eta Muscae at a distance of roughly 8,000 light-years. Its strongly pinched, symmetrical shape gives it its name. NGC 5189, on the border with Circinus at an estimated 1,750 light-years, looks decidedly less tidy: multiple ejections of material from its ageing central star, apparently twisted by the gravitational influence of a likely binary companion, create a complex, irregular structure. IC 4191 lies to the west of Eta Muscae and presents as a compact, bluish nebula of magnitude 10.6 thought to be some 10,750 light-years distant. NGC 4071, west of Epsilon Muscae, is a large, diffuse nebula of magnitude 12.7 with a magnitude 12 central star, estimated to be around 4,000 light-years away. Each of these represents a different chapter of the same story: a star that has exhausted its nuclear fuel and is sloughing off its outer layers into intricate glowing shells.
09 Two Ancient Globular Clusters
Musca carries two globular clusters worth seeking out, both partially dimmed by intervening dust near the galactic plane. NGC 4833, near Delta Muscae, was catalogued by Lacaille in 1755 and lies 21,200 light-years from Earth. NGC 4372, positioned near Gamma Muscae, is fainter and more spread out in apparent size, sitting 18,900 light-years from Earth and 23,000 light-years from the centre of the Milky Way — placing it well out in the galactic halo. Its extremely low metallicity, meaning it contains very little of the heavy elements forged in earlier generations of stars, marks it as one of the oldest globular clusters in the entire Milky Way. Trailing southward from NGC 4372 is the Dark Doodad Nebula, an L-shaped dark nebula that appears as a dark river cutting through a rich starfield. Another dark nebula, BHR 71, also lies within the constellation. The Coalsack Nebula, primarily resident in Crux, pushes its dark border into Musca as well, contributing to the sense that this compact constellation sits within a particularly dust-rich stretch of the southern Milky Way.
10 Epsilon Muscae: A Giant in Its Final Chapter
Epsilon Muscae offers a striking lesson in how dramatically stars can change over their lifetimes. Originally between 1.5 and 2 times the mass of the Sun, this star has exhausted the fuel at its core and expanded into a red giant of spectral type M5III. It has swollen to 130 times the Sun's diameter — large enough that, if placed at the centre of our solar system, it would engulf the orbit of the Earth. At the same time, its luminosity has grown to between 1,800 and 2,300 times that of the Sun. It is a semiregular variable, cycling between magnitudes 3.99 and 4.31 over roughly 40 days as its outer layers pulse in an unsteady rhythm. Despite lying at a similar distance of around 302 light-years to the Lower Centaurus Crux association stars, Epsilon moves at roughly 100 kilometres per second and shares no common origin with them. It is simply a chance neighbour on the sky, a much older and more evolved star caught in the same line of sight as its much younger, hotter companions.
11 The Constellation's Boundaries and Size
Musca covers 138 square degrees of sky, which is 0.335 percent of the entire celestial sphere, placing it 77th in size among the 88 recognised constellations. It is hemmed in on all sides by neighbours: Crux to the north, Carina to the west, Chamaeleon to the south, Apus and Circinus to the east, and Centaurus to the northeast. The International Astronomical Union adopted the three-letter abbreviation Mus in 1922. The formal boundaries were set by Belgian astronomer Eugène Delporte in 1930 as a six-sided polygon. In equatorial coordinates, the constellation spans right ascensions from 11 hours 19.3 minutes to 13 hours 51.1 minutes and declinations from −64.64 degrees to −75.68 degrees. The entire constellation is visible only to observers south of latitude 14 degrees north, which means it remains permanently below the horizon for the vast majority of people living in North America, Europe, and northern Asia. Altogether, 62 stars within Musca's boundaries are brighter than magnitude 6.5 — the traditional naked-eye limit.
12 Contact Binaries and Neutron Stars Deeper
Beyond its well-known variables, Musca harbours several extreme close-binary systems. TU Muscae, located roughly 15,500 light-years from Earth, pairs two massive hot stars of spectral types O7.5V and O9.5V, with masses of 23 and 15 times that of the Sun. The two are so close that they physically touch, forming what astronomers call an overcontact binary — their outer layers are in direct contact. As they orbit each other every approximately 1.4 days, they alternately eclipse one another as seen from Earth, causing the system's brightness to vary between magnitudes 8.17 and 8.75; this behaviour classifies it as a Beta Lyrae variable. GR Muscae is a different kind of extreme system: an X-ray binary in which a neutron star with a mass between 1.2 and 1.8 times that of the Sun is in close orbit with a low-mass companion thought to be approximately one solar mass. SY Muscae rounds out this zoo of interacting pairs as a symbiotic system in which a red giant shares mass with a white dwarf without forming an accretion disk or triggering periodic eruptions, varying between magnitudes 10.2 and 12.7 over a period of 624.5 days.