Musca (“the fly”) is a small southern sky constellation which was created by Petrus Plancius in the late 16th century, with the astronomer having based it upon the observations made by Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman while on their voyage to the East Indies (Southeast Asia). The constellation’s brightest star is Alpha Muscae, a blue-white subdwarf found 315 light years from Earth that shines with a visual magnitude of 2.69.
Musca is ranked 77th out of the 88 recognized constellations, and lies in the southern celestial heavens to the south of Crux, the smallest of all constellations. It is visible to observer situated between +10° and -90° of latitude, but is best seen in the month of May. Bordering the constellations of Musca are Apus, Carina, Centaurus, Chamaeleon, Circinus and Crux (the Southern Cross).
Bayer Constellation Family
Musca is part of the Johann Bayer family of constellations, which includes several southern constellations mostly named after exotic animals. These include Hydrus, Dorado, Volans, Apus, Pavo, Grus, Phoenix, Tucana, Indus and Chamaeleon.
Dutch explorer Pieter Dircksz Keyser called the constellation De Vlieghe, meaning “the fly” in his native language, with Dutch cartographer Petrus Plancius later adding it to his list of 12 southern sky constellations. In 1603, Johann Bayer included this constellation in his star atlas, Uranometria, although by the new name Apis (Bee), which it became known as until 1763 when French astronomer Nicolas Louis de Lacaille called it Musca Australis (Southern Fly) to differentiate it from a now obsolete constellation known as Musca Borealis (Northern Fly). After the latter was merged with the constellation of Aries in 1929, Musca Australis was shortened to just Musca.
– Alpha Muscae is a blue-white subdwarf star (B2 IV-V) located around 315 light years from our solar system. It shines with a visual magnitude of 2.69, making it the brightest star in Musca, but as a Beta Cephei variable it shows a subtle 1% variation in its luminosity due to surface pulsations. Alpha Muscae possesses 8.8 solar masses, 4.8 times our sun’s radius, and is 4,000 times more bright. It also rotates swiftly at a velocity of around 114 kilometers per second.
– Beta Muscae is a binary star system around 340 light years away whose two stars have an orbital period of 194 years. Both stars are blue-white dwarves and have a combined visual magnitude of 3.05 when viewed from Earth.
– Delta Muscae, the constellation’s third brightest star, is actually a binary star system whose main component is an orange giant (K2III) situated around 91 light years distant. It is around 8 times bigger than the Sun, and shines with an apparent visual magnitude of 3.61.
Other notable stars in Musca includes the white giant star Lambda Muscae of magnitude 3.68; the blue-white main sequence dwarf Gamma Muscae of magnitude 3.84; and the red giant star Epsilon Muscae of magnitude 4.11.
Notable Deep Sky Objects
There are no Messier objects in Musca, although it does contains some notable deep-sky objects, such as the globular cluster NGC 4822, NGC 4833 and NGC 4372. Nebulae in Musca include:
– Spiral Planetary Nebula (NGC 5189) is 3 light-years wide nebula located 3,000 light years away with a visual magnitude of 8.2. It is S-shaped, hence its name, with a possible explanation for its unusual shape being its central dying white dwarf star having a binary companion which then influences the pattern of gas and radiation being ejected from it. Thus far, however, no such visual companion has been observed.
– Dark Doodad Nebula is a dark nebula that is around 30 light years in length, and situated 700 light years from our solar system. This molecular cloud is found close to the globular cluster NGC 4372, and is one of the closest stellar nurseries to Earth.
– Hourglass Nebula (MyCn 18) is a planetary nebula found 8,000 light years away that has a visual magnitude of 13. It is also known as the Eye of God, because of the effect created by the structure’s central dying white dwarf star, and its two outer and one smaller central rings. An undiscovered companion star and its gravitational impact may help explain this iconic planetary nebula, with fast stellar winds also contributing to its beautiful hourglass shape.