Musca (the Fly) is a small southern constellation introduced by Dutch astronomer Petrus Plancius in the late 16th century. Situated just below the Southern Cross, it is one of the few constellations named after an insect.
Despite its modest size, Musca contains several fascinating deep-sky objects, including the long, dark molecular cloud known as the Dark Doodad Nebula, the unusually twisted planetary nebula NGC 5189, and the spectacular Hourglass Nebula.
Where Is Musca and When Can You See It?
Musca is the 77th-largest constellation, covering approximately 138 square degrees of the southern sky. It lies immediately south of Crux (the Southern Cross) and borders Apus, Carina, Centaurus, Chamaeleon, and Circinus.
The best time to observe Musca is April through June, particularly May, when it is well placed in the evening sky. The constellation is visible throughout much of the Southern Hemisphere and is circumpolar from many southern latitudes. It cannot be seen from Britain.
To locate Musca, first identify the four bright stars of the Southern Cross. Look immediately south of Crux for Alpha and Beta Muscae, the two brightest stars in Musca. Together with several fainter stars, they form a small, elongated pattern beneath the Cross.
History of the Musca Constellation
Musca was introduced by Petrus Plancius using observations gathered by Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman during voyages to the East Indies in the late 1500s. The constellation was originally depicted as a fly and appeared in Johann Bayer’s 1603 star atlas, Uranometria, under the name Apis, meaning the Bee.
Over time, its name changed to Musca Australis (the Southern Fly), partly to distinguish it from a now-obsolete northern constellation called Musca Borealis. When the modern constellation boundaries were standardized in the 20th century, the southern constellation retained the shorter name Musca.
Because it lies far south, Musca was unknown to ancient Greek astronomers and has no established classical mythology.
Notable Stars in Musca
Image Credit: Torsten Bronger- Alpha Muscae – The brightest star in Musca, a hot blue-white B-type star approximately 315 light-years away, shining at magnitude 2.7. It is a Beta Cephei variable, showing small changes in brightness caused by pulsations within the star.
- Beta Muscae – A binary system approximately 340 light-years away, with a combined magnitude of about 3.1. Both components are hot blue-white stars that orbit one another over a period of roughly 190 years.
- Delta Muscae – An orange giant approximately 90 light-years away, shining at magnitude 3.6. It has expanded considerably since leaving the main sequence and is part of a stellar system.
- Lambda Muscae – A white star with an apparent magnitude around 3.7, making it one of the constellation’s brighter members.
- Gamma Muscae – A hot blue-white star approximately 325 light-years away, shining at magnitude 3.8. Like Alpha Muscae, it is a variable star.
- Epsilon Muscae – A cool red giant approximately 300 light-years away, with an apparent magnitude around 4.1.
Notable Deep-Sky Objects in Musca
Musca contains no Messier objects, but its position close to the Milky Way gives it a rich selection of star clusters, dark clouds, and planetary nebulae.
Dark Doodad Nebula — A Ribbon of Cosmic Dust
It lies near the globular cluster NGC 4372, although the two objects are at very different distances and are not physically associated.
The Dark Doodad is best appreciated in wide-field astrophotography, where its winding shape stands out against the surrounding stars.
NGC 5189 — The Spiral Planetary Nebula
NGC 5189 is a planetary nebula approximately 3,000 light-years away, notable for its complex, twisted appearance. Unlike the familiar circular shape of many planetary nebulae, NGC 5189 displays an intricate arrangement of arcs, knots, and filaments of glowing gas. Its unusual structure is associated with the evolution of its central star, which belongs to a binary system. Interactions between the stars and the surrounding material may help explain the nebula’s complicated shape.
NGC 5189 has an apparent magnitude around 8–9 and can be detected through moderate-sized amateur telescopes under dark skies, although its detailed structure is best revealed in photographs.
Hourglass Nebula — MyCn 18
The Hourglass Nebula (MyCn 18) is a planetary nebula approximately 8,000 light-years away. It is famous for its remarkably symmetrical, hourglass-shaped structure, revealed in detailed images taken by the Hubble Space Telescope.
The nebula consists of gas expelled by an aging star, with a narrow central region separating two expanding lobes. Its unusual shape may have developed through interactions involving stellar winds and possibly a companion star.
Although visually striking in photographs, MyCn 18 is faint and difficult to observe through amateur telescopes.
NGC 4833 and NGC 4372 — Globular Clusters
NGC 4833 is a globular cluster approximately 21,000 light-years away, containing a dense population of old stars. With an apparent magnitude around 7.8, it is accessible through binoculars or small telescopes under favorable southern skies.
NGC 4372 is another globular cluster, approximately 19,000 light-years away. It appears close to the Dark Doodad Nebula in the sky, creating an attractive pairing for wide-field astrophotography.
Both clusters are ancient stellar systems associated with the Milky Way’s halo.