Constellations: Musca 'the Fly' Content from the guide to life, the universe and everything

Constellations: Musca 'the Fly'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus
Cepheus | Cetus | Chamæleon | Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus
Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
Hydra | Hydrus | Indus | Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra | Mensa | Microscopium | Monoceros
Musca | Norma | Octans | Ophiuchus | Orion | Pavo | Pegasus | Perseus | Phoenix | Pictor | Pisces | Piscis Austrinus
Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Alas, alas! How very soon the silly little fly,
Hearing his wily, flattering words, came slowly flitting by;
With buzzing wings she hung aloft, then near and nearer grew,
Thinking only of her brilliant eyes and green and purple hue,
Thinking only of her crested head. Poor, foolish thing! At last
Up jumped the cunning spider, and fiercely held her fast;
He dragged her up his winding stair, into the dismal den –
Within his little parlor – but she ne'er came out again!

– Mary Howitt (1799 - 1888) The Spider and the Fly

Name:Musca (Latin: 'fly')
Short form:Mus
Previously:Apis 'the Bee'
Area:138 sq deg
Co-ordinates1:Right Ascension 12h, Declination −70°
Origin:Modern (16th Century)

Musca is a small southern constellation the main stars of which have an arm of the Milky Way as a backdrop. It shares its borders with Centaurus, Crux, Carina, Chamæleon, Apus and Circinus. There are no Messier objects due to its extreme southerly position. However, the uncanny-looking Hourglass Nebula more than makes up for this.


The fly is one of a dozen constellations delineated by the Dutch astronomers Pieter Dirkszoon Keyser and Frederick de Houtman during their voyage to the southern seas between 1595 and 1597 on board the Hollandia, although they drew it as a bee which they named Apis. This is how it appeared in Johann Bayer's Uranometria (star catalogue) of 1603. It was then changed to Musca Apis (the fly bee) by Edmond Halley. In 1752, the French astronomer Nicolas Louis de Lacaille (1713 - 1762) decided it should be known as Musca Australis (the southern fly). The 'Australis' moniker was to differentiate it from its northerly cousin, Musca Borealis. Since the International Astronomical Union chose to have Musca Borealis' stars absorbed by Aries2, the Australis bit was no longer necessary and today the constellation is known as just Musca.


The scientific star names are simple to understand (if you know your Greek alphabet). For example, the 'alpha' star means that it is the brightest star in that constellation. Combined with the genitive name, this is known as the 'Bayer designation'. Some stars have proper names as well, but there are no named stars in Musca. Other stars, for example, HD 100546, are known by their catalogue number.

Stars of Musca

Alpha Muscae is a variable star of the beta Cephei type.

HD 100546 is an interesting star because it has a protoplanetary disc. The boulders surrounding the star are known as proplyds, the building blocks needed to form a solar system. It has an unconfirmed companion, HD 100546 b, which could be a brown dwarf (failed star) or a superjovian planet that is 20 times the mass of Jupiter, our Solar System's largest planet.

Delta Muscae, an orange dwarf, is a relative neighbour of ours, at a distance of 91 light years3. Its celestial co-ordinates are virtually the same as globular cluster NGC 4833, but that is just line of sight from our vantage point; NGC 4833 is 18,000 light years away.

Like delta, blue-white dwarf gamma Muscae appears to be a close companion of globular cluster NGC 4372 in images taken from Earth. In reality, gamma Muscae is 320 light years distant, and NGC 4372 is approximately 25,700 light years further away.

Star Table

StarDesignation or
catalogue number
Brightness (mag)Distance
(light years)
Spectral classification
and/or comments
α Musalpha Muscae+2.69 var300Blue-white subgiant
β Musbeta Muscae+3.04310Binary star system
λ Muslambda Mus+3.6130White subgiant
δ Musdelta Muscae+3.6291Orange dwarf
γ Musgamma Muscae+3.87320Blue-white dwarf
ε Musepsilon Muscae+4300Red dwarf
μ Musmu Muscae+4.75435Orange dwarf
η Museta Muscae+4.8400Blue-white dwarf
HD 100546KR Muscae+6.7 var335Protoplanetary disc
HD 111232HIP 62534+7.6 var94.5Has a planet

New General Catalogue (NGC) and Index Catalogue (IC)

The New General Catalogue (NGC) was compiled by John Louis Emil Dreyer (director of the Armagh Observatory from 1882 to 1916). This was later expanded to include newer discoveries, and is being continually updated as the NGC/IC Project. Other deep-space objects feature in different catalogues, for example, The Hourglass Nebula has the scientific name MyCn18.

The Spiral Nebula (NGC 5189) is a stunningly beautiful planetary nebula, a dying star which has ejected all of its surface, forming an 'S' shape like a spiral galaxy.

NGC 4815 is an open cluster with luminosity; it has been compared to the Hyades cluster in Taurus.

NGC 4372 is a fairly faint globular cluster. It features in the Caldwell Catalogue of English astronomer Sir Patrick Moore, host of the BBC's The Sky At Night, as Caldwell 108. Just north of NGC 4372 is the non-catalogued Doodad dark nebula. The bright star in the image below the Doodad nebula, and to the left of globular cluster NGC 4372, is gamma Muscae.

NGC/IC Table

CatalogueTypeBrightness (m)Distance
(light years)
NGC 4372Globular cluster+7.826,000Central concentration class XII (lowest)
NGC 4833Globular cluster+11.718,000Central concentration class VIII (medium)
NGC 4463Open cluster+7.23,42050+ stars
NGC 4815Open cluster+8.68,000100+ stars
NGC 5189Planetary nebula+103,100The Spiral Nebula
IC 4191Planetary nebula+11.514,400Discovered in 1907
by Williamina Fleming

The Hourglass Nebula

The Hourglass Nebula (MyCn18) was imaged by the Hubble Space Telescope (HST). The outer layers of the star have been ejected, causing a symmetrical effect. The central portion, the dying star, looks remarkably like a human eye.

The planetary nebula is one of a range of astonishing pictures featured on the Astronomy Picture of the Day website.

National Geographic magazine displayed it on its front cover in 1997. The editors said: 'Astronomers looked 8,000 light years into the cosmos with the HST, and it seemed that the eye of God was staring back.' The HST image of the Hourglass Nebula was also reproduced for the cover of rock band Pearl Jam's 2000 album Binaural.

Extrasolar Planets in Musca

Up to 2008, one extrasolar planetary system has been confirmed in the constellation Musca. Figures given in the table below contain confirmed planetary data only: the length of the planet's orbital period around its parent star, which we know of as a year, and the planetary mass compared with that of Jupiter, known by astronomers as the 'Jovian scale'. HD 111232 is a yellow dwarf that is smaller than our Sun. The planet HD 111232 b is a gas giant and orbits well out of range of the system's habitable zone.

Extrasolar Planets Table

Star name or
catalogue number
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
HD 111232HD 111232 b6.81,1432004Gas giant
HD 112410HD 112410 b9.2124.62013Hot superjovian
HD 108341HD 108341 b3.51,1292014Gas giant

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2By the 19th Century there were over 100 constellations in existence, honouring some weird and wacky objects that were in vogue at the time. In 1922, the IAU eliminated all but the now officially recognised 88.3A light year is the distance light travels in one year, roughly 5.88 trillion miles, or 9.46 trillion km.

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