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Musca
Constellation
Musca
List of stars in Musca
AbbreviationMus
GenitiveMuscae
Pronunciation
Symbolismthe Fly
Right ascension11h 19.3m to 13h 51.1m [1]
Declination−64.64° to −75.68°[1]
QuadrantSQ3
Area138 sq. deg. (77th)
Main stars6
Bayer/Flamsteed
stars		13
Stars brighter than 3.00m1
Stars within 10.00 pc (32.62 ly)1
Brightest starα Mus (2.69m)
Nearest starGliese 440
Messier objects0
Bordering
constellations
Visible at latitudes between +10° and −90°.
Best visible at 21:00 (9 p.m.) during the month of May.

Musca (Latin for 'the fly') is a small constellation in the deep southern sky. It was one of 12 constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman, and it first appeared on a celestial globe 35 cm (14 in) in diameter published in 1597 (or 1598) in Amsterdam by Plancius and Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer's Uranometria of 1603. It was also known as Apis (Latin for 'the bee') for 200 years. Musca remains below the horizon for most Northern Hemisphere observers.

Many of the constellation's brighter stars are members of the Scorpius–Centaurus association, a loose group of hot blue-white stars that appears to share a common origin and motion across the Milky Way. These include Alpha, Beta, Gamma, Zeta2 and (probably) Eta Muscae, as well as HD 100546, a blue-white Herbig Ae/Be star that is surrounded by a complex debris disk containing a large planet or brown dwarf and possible protoplanet. Two further star systems have been found to have planets. The constellation also contains two cepheid variables visible to the naked eye. Theta Muscae is a triple star system, the brightest member of which is a Wolf–Rayet star.

History

[edit]
Musca (as Apis) can be seen in the upper right of this extract from Bayer's Uranometria of 1603

Musca was one of the 12 constellations established by the astronomer Petrus Plancius from the observations of the southern sky by the Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman, who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. De Houtman included it in his southern star catalogue in 1598 under the Dutch name De Vlieghe, "The Fly".[2] They assigned four stars to the constellation, with a star that would be later designated as Beta Muscae marking the head, Gamma the body, and Alpha and Delta the left and right wings, respectively.[3] It first appeared on a 35-cm-diameter (14-in) celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius, though was unnamed.[4] The first depiction of this constellation in a celestial atlas was in the German cartographer Johann Bayer's Uranometria of 1603,[5] though Bayer termed it Apis— "the Bee", a name by which it was known for the next two centuries. A 1603 celestial globe by Willem Blaeu depicts it as providing nourishment for the nearby constellation Chamaeleon—its tongue trying to catch the insect.[4]

The French explorer and astronomer Nicolas Louis de Lacaille called it la Mouche on the 1756 version of his planisphere of the southern skies. Jean Fortin retained the French name in 1776 for his Atlas Céleste, while Lacaille Latinised the name for his revised Coelum Australe Stelliferum in 1763.[6] Lacaille renamed it to Musca Australis, the Southern Fly—Australis, since it counterparted the now discarded constellation of Musca Borealis composed of a few stars in Aries, and to avoid confusion with Apus. Today, the name is simply Musca.[7] It is the only official constellation depicting an insect.[8]

The Kalapalo people of Mato Grosso state in Brazil called Alpha and Beta Muscae (along with Beta and Kappa Crucis) Kutsu anangagï "Ornate Hawk-Eagle's double flutes".[9] The Wardaman people of the Northern Territory in Australia perceived the main stars of Musca as a ceremonial boomerang, part of the Central Arena—a sacred area surrounding the constellation Crux that depicts the lightning creation beings and where they teach Wardaman customs; Alpha and Beta also signified a ceremonial headband, while Gamma and Delta represented two armbands.[10] In central Australia, the Arrernte and Luritja peoples living in on a mission in Hermannsburg viewed the sky as divided between them, east of the Milky Way representing Arrernte camps and west denoting Luritja camps. The stars of Musca, along with Fomalhaut, Alpha Pavonis, and Alpha and Beta Gruis, were all claimed by the Arrernte.[11]

Characteristics

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Musca is bordered by Crux to the north, Carina to the west, Chamaeleon to the south, Apus and Circinus to the east, and Centaurus to the northeast. Covering 138 square degrees and 0.335% of the night sky, it ranks 77th of the 88 constellations in size.[12] The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Mus".[13] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of six segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 11h 19.3m and 13h 51.1m , while the declination coordinates are between −64.64° and −75.68°.[1] The whole constellation is visible to observers south of latitude 14°N.[14][a]

Features

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Stars

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See also: List of stars in Musca
Musca as seen by the naked eye

Lacaille charted and designated 10 stars with the Bayer designations Alpha to Kappa in 1756. He catalogued stars that became Lambda and Mu, but did not designate them as he considered them informes as they lay outside the asterism proper. Francis Baily considered them part of Musca, and Gould gave them their Bayer designations. Baily also dropped Kappa, which he felt was too faint to warrant a name, and designated two adjacent stars as Zeta1 and Zeta2. These last two stars are 1° apart, quite far to be sharing a Bayer designation. Lacaille had originally labelled the fainter one as Zeta, while Baily presupposed he had meant to label the brighter one. Reluctant to remove Lacaille's designation, he gave them both the Zeta designation.[15] Altogether there are 62 stars brighter than magnitude 6.5 in the constellation.[14]

The pattern of the brightest stars resembles that of Ursa Minor, in that the stars form a pattern reminiscent of a bowl with a handle.[12] Lying south-southeast of Acrux in neighbouring Crux is Alpha Muscae.[16] It is the brightest star in the constellation with an apparent magnitude of 2.7. Lying around 310 light-years away, it is a blue-white star of spectral type B2IV-V that is around 4520 times as luminous and 8 times as massive as the Sun. The star is a Beta Cephei variable with about 4.7 times the Sun's diameter, and pulsates every 2.2 hours, varying by 1% in brightness. A nearby star of magnitude 13 may or may not be a companion star.[17] Marking the fly's tail is Gamma Muscae,[16] a blue-white star of spectral type B5V that varies between magnitudes 3.84 and 3.86 over a period of 2.7 days. It is a variable of a different type, classed as a slowly pulsating B star, a type of variable.[18] It is around five times as massive as the Sun.[19]

Beta Muscae is a binary star system around 341 light-years distant that is composed of two blue-white main-sequence stars of spectral types B2V and B3V that orbit each other every 194 years. They are eight and six times as massive as the Sun, respectively, and have about 3.5 times its diameter.[20] Zeta2 Muscae is a white main sequence star of spectral type A5V around 330 light-years distant from Earth.[21] It is part of a triple star system with faint companions at 0.5 and 32.4 arc seconds distance.[22] Eta Muscae is a multiple star system, the two main components forming an eclipsing binary that has a combined spectral type of B8V and magnitude of 4.77 that dips by 0.05 magnitude every 2.39 days.[23] Alpha, Beta, Gamma, HD 103079, Zeta2 and (likely) Eta are all members of the Lower Centaurus Crux subgroup of the Scorpius–Centaurus association, a group of predominantly hot blue-white stars that share a common origin and proper motion across the galaxy.[24][25]

Delta and Epsilon mark the fly's left wing and right wing, respectively.[16] With an apparent magnitude of 3.62, Delta is an orange giant of spectral type K2III located around 91 light-years away.[26] Epsilon Muscae is a red giant of spectral type M5III and semiregular variable that ranges between magnitudes 3.99 and 4.31 over approximately 40 days.[27] It has expanded to 130 times the Sun's diameter and 1800 to 2300 its luminosity. It was a star originally 1.5 to 2 times as massive as the Sun. Although of a similar distance—around 302 light-years—to the stars of the Lower Centaurus Crux subgroup, it is moving much faster at around 100 km/s and does not share a common origin.[28] To the northwest lies Mu Muscae, an orange giant of spectral type K4III that varies between apparent magnitude 4.71 and 4.76, and has been classified as a slow, irregular variable.[29] Near Mu is Lambda Muscae, the third-brightest star in the constellation and a white main-sequence star of spectral type A7V around 128 light-years distant from Earth.[30]

Located near Alpha is R Muscae,[16] a classical Cepheid variable ranging from apparent magnitude 5.93 to 6.73 over 7.5 days. It is a yellow-white supergiant ranging between spectral types F7Ib and G2Ib,[31] located around 2037 light-years away.[32] S Muscae is likewise a classical Cepheid, a yellow-white supergiant ranging between spectral types F6Ib and G0Ib and magnitudes 5.89 to 6.49 over a period of 9.66 days.[33] A luminous star around 5.9 times as massive as the Sun, it is a binary star with a blue-white main-sequence star companion likely to be of spectral type B3V to B5V with a mass of just over 5 solar masses,[34] one of the hottest and brightest companions of a cepheid known. The two stars orbit each other every 505 days.[35]

Theta Muscae is a triple star system thought to be around 7,500 light-years distant.[36] It consists of a spectroscopic binary system composed of the Wolf–Rayet star (spectral type: WC5 or 6) and an O-type main-sequence star (spectral type: O6 or O7) that orbit each other every 19 days and a blue supergiant (spectral type: O9.5/B0Iab) set about 46 milliarcseconds apart from them. If the system's estimated distance from Earth is accurate, the binary stars are about 0.5 astronomical units (AU) apart and the supergiant about 100 AU apart from them.[37] All three are highly luminous; combined, they are likely to be over a million times as luminous as the Sun.[36] TU Muscae is a binary star system located around 15,500 light-years away made up of two hot, luminous, blue main-sequence stars of spectral types O7.5V and O9.5V,[38][39] with masses 23 and 15 times that of the Sun. The stars are so close that they are in contact with each other (overcontact binary) and are classed as a Beta Lyrae variable as their light varies from Earth as they eclipse each other.[38] The system ranges from apparent magnitude 8.17 to 8.75 over around 1.4 days.[40]

Also known as Nova Muscae 1983, GQ Muscae is a binary system consisting of a white dwarf and small star that is about 10% as massive as the Sun. The two orbit each other every 1.4 hours. The white dwarf accumulates material from its companion star via its accretion disc. After a certain amount has accumulated, the star erupts, as it did in 1983, reaching a magnitude of 7.2.[41] Discovered with a magnitude of 7.1 on 18 January 1983,[42] it was the first nova from which X-rays were detected.[43] The soft X-ray transient GRS 1124-683 (also known as Nova Muscae 1991) is a binary object consisting of an orange main-sequence star (GU Muscae) of spectral type K3V–K4V and a black hole of around six solar masses.[44] During the 1991 outburst which led to its discovery, radiation was produced through a process of positron annihilation.[45] GR Muscae is an X-ray source composed of a neutron star of between 1.2 and 1.8 times the mass of the Sun and a low-mass star likely to be around the mass of the Sun in close orbit.[46] Finally, SY Muscae is a symbiotic star system composed of a red giant and white dwarf, where although the larger star is transferring mass to the smaller, no periodic eruption occurs nor does an accretion disc form.[47] The star system varies in magnitude from 10.2 to 12.7 over a period of 624.5 days.[48] V415 Muscae is a nova that had an outburst on 8 June 2022 with an apparent magnitude of +8.7.[49]

The Coalsack Nebula can be seen as the large, dark region near the top of the photo. It extends into the northeast of Musca. The vertical dark column in the lower right of the image is the Dark Doodad Nebula.

Three star systems have been discovered to have exoplanets. HD 111232 is a yellow main-sequence star around 78% as massive as the Sun around 95 light-years distant. It has a planet (HD 111232 b) around 6.8 times the mass of Jupiter that has an orbital period around 1143 days.[50] HD 112410 is a yellow giant of spectral type G8III located around 439 light-years distant.[51] With around 1.54 times the mass of the Sun, it is cooling and expanding along the red-giant branch, having left the main sequence after exhausting its core supply of hydrogen fuel. It has a substellar companion calculated to have a mass 9.2 times that of Jupiter and an orbital period of 124.6 days at a distance around 0.57 AU.[52] Yet another member of the Lower Centaurus Crux subgroup,[24] HD 100546 is a young, blue-white Herbig Ae/Be star of spectral type B9V that has yet to settle on the main sequence—the closest of these stars to Earth around 320 light-years distant.[53][54] It is surrounded by a circumstellar debris disk from a distance of 0.2 to 4 AU, and again from 13 AU out to a few hundred AU, with evidence for a protoplanet forming at a distance around 47 AU.[53] A gap exists between 4 and 13 AU, which appears to contain a large planet around 20 times the mass of Jupiter,[55] although further examination of the disk profile indicates it might be a more massive object such as a brown dwarf or more than one planet.[56] LP 145-141 is a white dwarf located 15 light-years distant—the fourth-closest to the Solar System.[57] It is considered a good candidate to look for Jupiter-like planets, on account if its proximity and mass.[58]

Deep-sky objects

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Located on the border with Circinus is the unusual planetary nebula NGC 5189,[8] estimated to be around 1750 light-years away from Earth.[59] Its complex structure is due to multiple ejections of material from the ageing central star, which are distorted by the presence of a likely binary companion.[60] Located 2.4° east of Eta Muscae is the magnitude-12.9 Engraved Hourglass Nebula (MyCn 18),[61] which lies about 8000 light-years distant from Earth.[62] To Eta's west lies IC 4191, a compact bluish planetary nebula of magnitude 10.6,[63] thought to lie around 10,750 light-years away from Earth.[64] West of Epsilon Muscae is NGC 4071, a large, diffuse planetary nebula of magnitude 12.7 with a magnitude 12 central star,[63] thought to lie around 4000 light-years away from Earth.[64] The Coalsack Nebula is a dark nebula located mainly in neighbouring Crux that intrudes into Musca.[65] NGC 4463 is an open cluster located on its southwestern border.[66] Around five light-years across, it is located around 3400 light-years away.[12]

The comparatively old globular cluster NGC 4833 near Delta Muscae was catalogued by Lacaille in 1755.[8] It is 21,200 light-years distant and somewhat obscured by dust clouds near the galactic plane. The globular cluster NGC 4372 near Gamma Muscae is fainter and likewise partially obscured by dust, but spans more arc minutes.[67] It is 18,900 light-years away from Earth and 23,000 light-years distant from the centre of the Milky Way. Its extremely low metallicity indicates it is very old—one of the oldest clusters in the Milky Way.[68] Extending south from it is the Dark Doodad Nebula, resembling a dark L-shaped river through a bright field of stars.[69] Another dark nebula in the constellation is BHR 71.

See also

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Notes

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Musca

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Musca (genitive: Muscae; abbreviation: Mus) is a small constellation in the southern celestial hemisphere, representing a fly. It occupies an area of 138 square degrees, ranking 77th in size among the 88 modern constellations. It lies in the third quadrant of the southern sky (SQ3) and is bordered by the constellations Apus, Carina, Centaurus, Chamaeleon, Circinus, and Crux, with its brightest stars forming a compact pattern near the Milky Way's dark Coalsack Nebula. Musca is one of twelve southern constellations created by Dutch astronomer Petrus Plancius around 1597–1598 based on observations from the 1595–1597 voyages of navigators Pieter Dirkszoon Keyser and Frederick de Houtman. It first appeared unnamed on Plancius's globe of 1598 and was depicted as Apis (the Bee) in Johann Bayer's 1603 Uranometria due to a misidentification, later correctly named Musca Australis, the Southern Fly, in John Flamsteed's Historia Coelestis Britannica (1729). The constellation's brightest star is Alpha Muscae, a blue-white of spectral class B2 IV–V with an of 2.69, located approximately 310 light-years away. Other principal stars include Beta Muscae, a of two blue-white main-sequence stars approximately 340 light-years distant, and Gamma Muscae, a blue-white main-sequence star of spectral class B5 V. Musca hosts notable deep-sky objects, including the NGC 5189 and the Nova Muscae 1991 (GU Muscae). These features make Musca a rich target for observers studying , binary dynamics, and galactic structure within the .

Historical Background

Creation and Naming

The constellation Musca originated from observations of the southern skies conducted by Dutch navigators and during their voyages to the from 1595 to 1597. These observations were incorporated into new southern constellations by the Dutch cartographer and theologian , who added the constellation to the southern skies around 1597–1598 as part of a set of twelve additions to the traditional Ptolemaic catalog, initially depicting it unnamed on a globe published in 1598 by , where it was labeled De Vlieghe, Dutch for "the Fly," though some early depictions left it unnamed. In 1603, German celestial cartographer included the constellation in his influential star atlas Uranometria, but renamed it Apis, Latin for "the Bee," possibly due to a misinterpretation of its form or to avoid confusion with an existing northern fly figure; this designation endured in astronomical literature for roughly two centuries. French astronomer Nicolas Louis de Lacaille revisited the southern constellations during his expedition to the from 1750 to 1752, cataloging nearly 10,000 stars and refining boundaries. In his posthumously published Coelum Australe Stelliferum (1763), Lacaille redesignated the figure as Musca Australis, or "Southern Fly," to clearly differentiate it from the obsolete northern constellation Musca Borealis, originally created by in 1612 as Apis (the Bee) using faint stars near Aries and later renamed by in 1690—and to emphasize its insectile outline. The simplified name Musca was standardized in 1922 by the during its first in , where it formalized the boundaries and nomenclature of the 88 modern constellations, incorporating Lacaille's southern additions while discarding obsolete figures like Musca Borealis.

Cultural Significance

, located entirely in the , was invisible from the latitudes of and , resulting in the absence of any significant mythological associations from those cultures. Among the people of central Brazil's region, the —straddling the boundary between Musca and —is interpreted as a celestial beehive, with the bright stars of the Southern Cross representing bees emerging from it in their traditional cosmology. In Australian Indigenous astronomy, the Wardaman people of the view the within the Musca region as a dark cave inhabited by the evil spirit-being Utdjungon, who emerges to cause harm if cultural taboos are violated, embedding moral lessons in their Dreamtime narratives. The of observe the emu-in-the-sky across the Milky Way's dark lanes, where the Coalsack forms the bird's head in the region near Musca and ; this celestial emu signals the seasonal availability of emu eggs, guiding hunting practices and reinforcing connections between sky patterns and terrestrial cycles.

Observational Properties

Visibility and Location

Musca occupies a position in the , with its boundaries defined by the spanning from 11h 19.3m to 13h 51.1m and from −64.64° to −75.68°. This places it entirely south of the , covering an area of 138 square degrees, which ranks it as the 77th largest constellation. Its compact size and faint overall appearance make it challenging to discern without , though its proximity to the prominent Southern Cross () serves as a useful reference for locating it. The constellation achieves best visibility in May for observers in the , when it reaches its highest point overhead during evening hours. It is —never setting below the horizon—for latitudes south of approximately 65°S, allowing continuous observation throughout the year in regions. Northward of 75°S, the constellation rises above the horizon at certain times but culminates lower in the sky; farther north, it becomes visible only partially or transiently. Musca remains invisible to most northern hemisphere observers beyond 14°N, limiting its accessibility from locations in , , and much of . Optimal viewing requires clear, light-pollution-free skies in the southern temperate zones, such as or , where its position near facilitates identification amid the Milky Way's glow.

Boundaries and Neighbors

The boundaries of the constellation Musca were officially delineated by Belgian astronomer Eugène Delporte in 1930, as adopted by the (IAU), using and lines based on the B1875.0 coordinates. These boundaries encompass an area of 138 square degrees, making Musca the 77th largest of the 88 modern constellations in terms of sky coverage. Musca is bordered by to the north, Carina to the west, to the south, and to the east, and to the northeast. The IAU has assigned the three-letter "Mus" to Musca, a standard used across astronomical . Unlike individual stars within it, the constellation as a whole lacks specific Bayer or Flamsteed designations, as those systems apply primarily to stellar cataloging rather than constellation outlines. In the 18th century, French astronomer Nicolas Louis de Lacaille contributed to the historical definition of southern constellation boundaries through his extensive mapping of the skies during his 1751–1752 expedition to the , adjusting figures like to distinguish smaller patterns from expansive ancient constellations such as .

Stellar Population

Principal Stars

The principal stars of Musca are its four brightest members, which define the outline of the fly and are visible to the from the . These stars vary in color and evolutionary stage, ranging from hot blue giants to cooler orange giants, providing a diverse within the constellation. Alpha Muscae is the brightest star in Musca, shining at an apparent visual magnitude of 2.69. It is classified as a blue-white subgiant of spectral type B2 IV-V and lies approximately 315 light-years from Earth. This hot, massive star rotates rapidly and is a key marker for the constellation's head. Beta Muscae, the second-brightest at a combined apparent magnitude of 3.05, is a blue-white main-sequence star system of spectral type B2 V for its primary component, situated about 341 light-years away. It appears as a visually striking close pair of bluish stars, separated by just 1.3 arcseconds, offering a challenging but rewarding sight for amateur astronomers with steady skies. Gamma Muscae has an of 3.84 and is a blue-white main-sequence dwarf of spectral type B5 V, located roughly 324 light-years distant. It contributes to the constellation's body, standing out among the hotter blue s due to its slightly cooler temperature. Delta Muscae, at magnitude 3.61, is an orange giant of spectral type III and the closest principal to at about 91 light-years. This evolved forms a key part of the "fly's body" in the asterism, contrasting with the dominant blue hues of the brighter members.

Variable Stars and Binaries

Theta Muscae is a prominent triple star system in Musca, featuring a Wolf-Rayet star of spectral type WC6 as its primary component, paired with an O9.5 supergiant in a close spectroscopic binary, and a more distant B-type companion. The system exhibits variability with an fluctuating around 5.50, attributed to the evolving nature of the Wolf-Rayet star's intense stellar winds. Located approximately 7,500 light-years away, Theta Muscae is associated with the G304.4-3.1, a filamentary structure identified through radio and optical observations, with its connection to the system confirmed via detailed imaging around 2010 and further refined in 2024 narrowband exposures revealing OIII emissions. This remnant, spanning about 0.5 degrees, provides evidence of past massive stellar activity in the region without direct causation from the current stars. R Muscae serves as a classical , pulsating with a period of 7.5 days and varying in between 5.93 and 6.73. At a distance of roughly 3,350 light-years, its has been instrumental in calibrating the for extragalactic distance measurements, offering insights into the star's evolutionary stage as a post-main-sequence . Observations highlight its role in refining cosmic distance ladders due to the precision of its pulsation properties. Similarly, S Muscae is another classical Cepheid in the constellation, displaying variability with a period of approximately 9.7 days and an range of 5.89 to 6.49, where it appears notably brighter at maximum light. Positioned about 2,600 light-years distant, this star is embedded in the young ASCC 69, aiding studies of Cepheid environments and their association with stellar aggregates for improved mass and age estimates. Its binary nature, with an orbital period of 507 days, adds complexity to analyses but enhances understanding of multiplicity in pulsating variables. V415 Muscae represents a recent classical nova outburst, discovered on June 8, 2022, by the All-Sky Automated Survey for Supernovae (ASAS-SN), reaching a peak of 8.7 in the g-band near the Musca border. Post-outburst monitoring by the American Association of Variable Star Observers (AAVSO) documented its rapid decline, characteristic of thermonuclear runaway on a surface, with the event providing data on nova evolution in a southern sky location. Pre-discovery images confirmed the outburst's onset, emphasizing the system's value for real-time spectroscopic follow-up. Beta Muscae forms a visual comprising two main-sequence B-type stars (B2V and B3V), orbiting each other with a period of about 194 years and an eccentricity of 0.6. The components maintain an average angular separation of around 1.3 arcseconds, corresponding to approximately 100 AU at their estimated of 340 light-years, allowing resolution with moderate telescopes and enabling orbital dynamics studies. This wide binary illustrates the prevalence of multiplicity among hot, massive stars in Musca, influencing their evolutionary paths through potential or dynamical interactions.

Exoplanet Systems

The constellation Musca harbors four confirmed systems, offering valuable insights into planetary architectures around main-sequence and pre-main-sequence stars. All detections rely on indirect methods, with no transiting planets identified to date, though two systems feature directly imaged companions. These systems span a range of host star types and planet masses, from candidate protoplanets to gas giants, and highlight the diversity of formation environments within this southern constellation. HD 100546, also known as KR Muscae, is a B9Vne Herbig Ae/Be star approximately 353 light-years distant, is a young (~5.5 million years old) system embedded in a complex . It hosts the candidate HD 100546 b, estimated at about 8.5 masses and orbiting at roughly 53 AU, detected via direct imaging in the near-infrared. This object is considered a key example of ongoing formation at large separations, with its spectrum showing evidence of clouds and possibly a ; a possible companion has also been proposed based on disk asymmetries, though its nature remains unconfirmed. Recent analyses, including high-contrast imaging and spectroscopic studies, continue to refine its properties and orbital parameters, underscoring its role in probing early planetary evolution. YSES-1, also known as TYC 8998-760-1, is a young K7V approximately 310 light-years away and about 17 million years old, resembling the Sun in mass and temperature. It hosts two directly imaged exoplanets: YSES-1 b, with a mass of about 14 masses and an of roughly 1,600 years at ~300 AU, and YSES-1 c, with a mass of about 6 masses and an of around 5,700 years at ~500 AU. The system was first imaged in 2020 using the , and further characterized in 2025 by the , providing insights into the early stages of planetary formation around a . The HD 111232 system features a G8V main-sequence star located 94 light-years away, with two massive companions detected through monitoring. HD 111232 b, a with a mass of 7.965 masses, has an of 1,169 days (~3.2 years) and was the first planet identified in the system in 2004 using the CORALIE spectrograph. A second outer companion, HD 111232 c, estimated at 18.063 masses with a much longer period of approximately 72 years, was confirmed in 2022 through extended datasets that accounted for stellar activity. This multi-planet architecture suggests dynamical stability over long timescales, with the inner planet's orbit placing it in a potentially temperate zone relative to the host. HD 112410, a G8III about 510 light-years distant, hosts a single known , HD 112410 b, with a minimum of 9.18 masses and an of 124.6 days, detected via observations in 2013. The planet's close-in orbit around an evolved host provides evidence that such systems can survive post-main-sequence stellar expansion, though detailed atmospheric characterization remains challenging without transit data. Confirmation relied on precise measurements from the FEROS and HARPS spectrographs, ruling out stellar oscillations as the signal source.

Deep-Sky Objects

Nebulae

The is a prominent located approximately 600 light-years from Earth, spanning about 7 by 5 degrees across the constellations of and Musca. This dense cloud of interstellar dust and gas effectively blocks visible starlight from background regions of the , creating a striking known as the "coal sack" against the brighter band. MyCn 18, also known as the , is a bipolar planetary nebula situated about 8,000 light-years away in Musca with an of 13.0. Its distinctive shape features intricate etchings and patterns formed by the interaction of a fast from the central with a surrounding equatorial disk of denser material. NGC 5189 is a complex spiral located roughly 1,800 light-years from , exhibiting an of 10.0. The displays asymmetric lobes and a multipolar structure, likely shaped by interactions involving its binary central , where orbital dynamics influence the ejection of material into filamentary and looped features. The Theta Muscae , designated G304.4-3.1, is a shell-type near the Wolf-Rayet star Theta Muscae, at a distance of approximately 7,400 light-years with a diameter of about 0.5 degrees. Optical imaging from 2024 reveals detailed filamentary structures within the remnant.

Star Clusters

Musca harbors two globular clusters, NGC 4833 and NGC 4372, which are among the deep-sky highlights of this southern constellation. These ancient stellar aggregates provide insights into the early formation of the , containing some of the galaxy's oldest stars. In contrast to regions rich in young stellar associations, Musca features no prominent open clusters, attributable to its position in a sparse field of lower stellar density away from the . NGC 4833 is a located approximately 21,200 light-years from , exhibiting an apparent visual magnitude of 8.2. It subtends an apparent diameter of 13.5 arcminutes on the sky and is classified as Shapley-Sawyer concentration class VIII, denoting a loosely concentrated core with gradually fading into the surrounding field. This cluster hosts over 100,000 and has an estimated age of 12 billion years, underscoring its role as a relic from the galaxy's formative epochs. NGC 4372, situated about 18,900 light-years distant, shines at an of 7.9 and covers 16 arcminutes in angular extent. Classified as concentration class IX—the loosest category on the Shapley-Sawyer scale—it displays a very diffuse structure with minimal central density. This metal-poor , with [Fe/H] ≈ -2.2, is approximately 12.5 billion years old and resides near the Way's halo, highlighting dynamical processes in the galaxy's outer regions.

References

  1. https://www.constellation-guide.com/constellation-list/musca-constellation/
  2. http://www.ianridpath.com/startales/musca.html
  3. https://science.nasa.gov/asset/hubble/planetary-nebula-ngc-5189/
  4. https://www.nature.com/articles/353050a0
  5. http://www.seasky.org/constellations/constellation-musca.html
  6. https://www.universetoday.com/articles/musca
  7. https://cseligman.com/text/atlas/musca.htm
  8. https://www.deepskyphotography.co.uk/musca.html
  9. http://judy-volker.com/StarLore/Myths/MuscaBorealis.html
  10. http://judy-volker.com/StarLore/Myths/Coalsack.html
  11. https://adsabs.harvard.edu/pdf/2020JAHH...23..390G
  12. http://www.aboriginalastronomy.com.au/content/topics/landscape/
  13. https://www.ayersrockresort.com.au/stories/emu-in-the-sky
  14. https://www.go-astronomy.com/constellations.php?Name=Musca
  15. https://earthsky.org/constellations/musca-the-fly/
  16. https://astro4edu.org/resources/diagram/bO379985GO52/
  17. https://www.aavso.org/constellation-names-and-abbreviations
  18. https://theskylive.com/sky/stars/alpha-muscae-star
  19. http://stars.astro.illinois.edu/sow/alphamus.html
  20. https://theskylive.com/sky/stars/beta-muscae-star
  21. http://assa.saao.ac.za/sections/double-and-variable-stars/double-stars/news-and-articles/double-star-challenge-beta-muscae/
  22. http://stars.astro.illinois.edu/sow/betamus.html
  23. https://www.universeguide.com/star/61199/gammamuscae
  24. https://www.universeguide.com/star/63613/deltamuscae
  25. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Theta+Mus
  26. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=R+Mus
  27. https://ned.ipac.caltech.edu/level5/ESSAYS/Evans/evans.html
  28. https://ui.adsabs.harvard.edu/abs/2014ApJ...785L..25E/abstract
  29. https://ui.adsabs.harvard.edu/abs/2022CBET.5135....1S/abstract
  30. https://ui.adsabs.harvard.edu/abs/2015ApJ...807...64Q/abstract
  31. https://science.nasa.gov/exoplanet-catalog/hd-100546-b/
  32. https://www.eso.org/public/news/eso2011/
  33. https://www.sci.news/astronomy/webb-two-young-exoplanets-yses-1-system-13981.html
  34. https://ui.adsabs.harvard.edu/abs/2004A&A...415..391M/abstract
  35. https://ui.adsabs.harvard.edu/abs/2022ApJS..262...21F/abstract
  36. https://exoplanetarchive.ipac.caltech.edu/overview/HD%20111232
  37. https://www.eso.org/public/news/eso1539/
  38. https://www.astronomy.com/science/coalsack-nebula/
  39. https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-99/
  40. https://science.[nasa](/page/NASA).gov/image-detail/hourglass-nebula/
  41. https://www.constellation-guide.com/hourglass-nebula/
  42. https://esahubble.org/images/opo9607a/
  43. https://www.astronomy.com/science/ngc-5189/
  44. https://academic.oup.com/mnras/article/448/2/1789/1057108
  45. https://www.aapod2.com/blog/snr-g3044-31-supernova-remnant
  46. https://academic.oup.com/mnras/article/401/3/1760/1093619
  47. https://noirlab.edu/public/education/constellations/musca/
  48. https://science.nasa.gov/missions/hubble/a-hubble-sky-full-of-stars/
  49. https://www.aanda.org/articles/aa/full_html/2014/07/aa23709-14/aa23709-14.html
  50. https://www.aanda.org/articles/aa/full_html/2015/07/aa25722-15/aa25722-15.html
  51. https://ui.adsabs.harvard.edu/abs/2014A&A...567A..69K/abstract
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