Orion's Sword is a compact asterism in the constellationOrion. It comprises three stars (42 Orionis, Theta Orionis, and Iota Orionis) and M42, the Orion Nebula, which together are thought to resemble a sword or its scabbard. This group is south of the prominent asterism, Orion's Belt. Fables and old beliefs are in Europe dominated or widely influenced by those of the Greco-Roman narratives. Beyond Europe this grouping is quite widely referenced as a weapon just as the majority of cultures perceived Orion's standout asymmetrical "hourglass" of seven very bright stars as a human.
An illustration of the hunter Orion, with the associated constellation.
Components
Orion Nebula and the surrounding stars that constitute Orion's Sword. The nebula hosts a stellar nursery, leading to the birth of multiple hot, young stars that make Orion's Sword so distinctive.
The Orion Nebula consists of one of the nearest (thus in the Milky Way Galaxy), massive molecular clouds (30 - 40 light years in diameter) about 1,300 light years from the solar system.[1] This makes the nebula potentially the closest HII region to Earth, a mass of hydrogen that has been ionized by nearby, hot, young stars.[2] Regions like this are called stellar nurseries, nurturing the birth of multiple young stars such as the Orion Nebula Star Cluster.[1] These are a hallmark of the asterism.
Main stars
42 Orionis, also called c Ori, is a B1V magnitude star in the northern half of the Orion nebula.[3]Theta Orionis has a more central position in the nebula, and is actually composed of a multi-star system.[4]Iota Orionis is one of the brightest in the collection, in the south of the Orion nebula. Iota Orionis is a spectroscopic binary system, with a variable magnitude of O9III.[5]
Scientific studies
Given the scientific significance of M42, Orion's Sword is a popular spot for stellar and protostellar studies. Using the Hubble Space Telescope, O'dell et al. focused on identifying previously unseen features of the nebula, such as high-ionization shocks, compact sources, and protoplanetary disks.[6] Some studies have focused on the sword region overall. Gomez & Leda found that less than half of the OB and Hα stars in this region are associated with well-defined stellar clusters.[7] This positional similarity, as well as the high star formation rates and gas pressure in the nearby molecular cloud, confirms the previous notion that old, foreground OB stars triggered star formation in this cloud.[7]
References in history and culture
In his De Astronomia, Hyginus describes the constellation Orion having three faint stars where the sword is depicted.[8]Aratus goes into significant detail about the Orion constellation as well, proclaiming: "Should anyone fail to catch sight of him (Orion) up in the heavens on a clear night, he should not expect to behold anything more splendid when he gazes up at the sky."[9]Cicero[10] and Germanicus,[11] the translators of Aratus's Phaenomena, expressed it as ensis, Latin for "sword". Arabic astronomers also saw this asterism as a sword (سيفsaif), calling it Saif al Jabbār, Sword of the Powerful One or Sword of the Giant.[12] Orion is one of the few constellations to have parallel identities in European and Chinese culture, given the name Shen, the hunter and warrior. Chinese astronomers made the sword a sub-constellation within Shen called Fa.[13]
In the myths of the Nama of Namibia and the western Cape, this was the arrow of the husband of the Pleiades, daughters of the sky god, who was represented by Orion's SW main star Rigel. When he fired his arrow at three zebras (Orion's belt) and missed, he was too afraid to retrieve the arrow due to its proximity to a fierce lion, represented by Betelgeuse. Therefore, he sits in the cold, suffering from hunger but too ashamed to return home. Regionally the prevailing cold breezes and currents come from that direction.[14] The Tswana to the east traditionally call the unusually bright nebula and its companions dintsa le Dikolobe, three dogs which chase the three pigs (the belt). This serves as an etiological myth for why pigs have their litters in the same season Orion is prominent in the sky.[14]
Orion's sword is referenced in the song "The Dark of the Sun" by Tom Petty on his 1991 album Into the Great Wide Open, in the line "saw you sail across a river underneath Orion's sword...". It is also mentioned in Jethro Tull's song "Orion", on their 1979 album Stormwatch, in the lines "Your faithful dog shines brighter than its lord and master, your jewelled sword twinkles as the world rolls by."
Gallery
The Orion constellation, with Orion's sword distinguished by M42.
How Orion appears in a clear sky. M42, and thus Orion's sword, is one of the brightest and most prominent features of the constellation.
The Orion Sword observed from Australia (stitching of 3 observations made with a Unistellar eVscope)
Corona Australis is a constellation in the Southern Celestial Hemisphere. Its Latin name means "southern crown", and it is the southern counterpart of Corona Borealis, the northern crown. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. The Ancient Greeks saw Corona Australis as a wreath rather than a crown and associated it with Sagittarius or Centaurus. Other cultures have likened the pattern to a turtle, ostrich nest, a tent, or even a hut belonging to a rock hyrax.
Andromeda is one of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy, and one of the 88 modern constellations. Located in the northern celestial hemisphere, it is named for Andromeda, daughter of Cassiopeia, in the Greek myth, who was chained to a rock to be eaten by the sea monster Cetus. Andromeda is most prominent during autumn evenings in the Northern Hemisphere, along with several other constellations named for characters in the Perseus myth. Because of its northern declination, Andromeda is visible only north of 40° south latitude; for observers farther south, it lies below the horizon. It is one of the largest constellations, with an area of 722 square degrees. This is over 1,400 times the size of the full moon, 55% of the size of the largest constellation, Hydra, and over 10 times the size of the smallest constellation, Crux.
Orion is a prominent set of stars visible during winter in the northern celestial hemisphere. It is one of the 88 modern constellations; it was among the 48 constellations listed by the 2nd-century astronomer Ptolemy. It is named for a hunter in Greek mythology.
The Orion Nebula is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion, and is known as the middle "star" in the "sword" of Orion. It is one of the brightest nebulae and is visible to the naked eye in the night sky with apparent magnitude 4.0. It is 1,344 ± 20 light-years (412.1 ± 6.1 pc) away and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light-years across. It has a mass of about 2,000 times that of the Sun. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula.
Auriga is a constellation in the northern celestial hemisphere. It is one of the 88 modern constellations; it was among the 48 constellations listed by the 2nd-century astronomer Ptolemy. Its name is Latin for '(the) charioteer', associating it with various mythological beings, including Erichthonius and Myrtilus. Auriga is most prominent during winter evenings in the northern Hemisphere, as are five other constellations that have stars in the Winter Hexagon asterism. Because of its northern declination, Auriga is only visible in its entirety as far south as -34°; for observers farther south it lies partially or fully below the horizon. A large constellation, with an area of 657 square degrees, it is half the size of the largest, Hydra.
Alnitak is a triple star system in the constellation of Orion. It has the designations ζ Orionis, which is Latinised to Zeta Orionis and abbreviated Zeta Ori or ζ Ori, and 50 Orionis, abbreviated 50 Ori. The system is located at a distance of several hundred parsecs from the Sun and is one of the three main stars of Orion's Belt along with Alnilam and Mintaka.
Iota Orionis is a multiple star system in the equatorial constellation of Orion the hunter. It is the eighth-brightest member of Orion with an apparent visual magnitude of 2.77 and also the brightest member of the asterism known as Orion's Sword. It is a member of the NGC 1980 open cluster. From parallax measurements, it is located at a distance of roughly 1,340 light-years from the Sun.
Messier 43 or M43, also known as De Mairan's Nebula and NGC 1982, is a star-forming nebula with a prominent H II region in the equatorial constellation of Orion. It was discovered by the French scientist Jean-Jacques Dortous de Mairan some time before 1731, then catalogued by Charles Messier in 1769. It is physically part of the Orion Nebula, separate from that main nebula by a dense lane of dust known as the northeast dark lane. It is part of the much larger Orion molecular cloud complex.
An asterism is an observed pattern or group of stars in the sky. Asterisms can be any identified pattern or group of stars, and therefore are a more general concept than the 88 formally defined constellations. Constellations are based on asterisms, but unlike asterisms, constellations outline and today completely divide the sky and all its celestial objects into regions around their central asterisms. For example, the asterism known as the Big Dipper comprises the seven brightest stars in the constellation Ursa Major. Another is the asterism of the Southern Cross, within the constellation of Crux.
The Catasterismi or Catasterisms is a lost work attributed to Eratosthenes of Cyrene. It was a comprehensive compendium of astral mythology including origin myths of the stars and constellations. Only a summary of the original work survives, called the Epitome Catasterismorum, by an unknown author sometimes referred to as pseudo-Eratosthenes.
The Orion molecular cloud complex is a star-forming region with stellar ages ranging up to 12 Myr. Two giant molecular clouds are a part of it, Orion A and Orion B. The stars currently forming within the complex are located within these clouds. A number of other somewhat older stars no longer associated with the molecular gas are also part of the complex, most notably the Orion's Belt, as well as the dispersed population north of it. Near the head of Orion there is also a population of young stars that is centered on Meissa. The complex is between 1 000 and 1 400 light-years away, and hundreds of light-years across.
Sh2-279 is an HII region and bright nebulae that includes a reflection nebula located in the constellation Orion. It is the northernmost part of the asterism known as Orion's Sword, lying 0.6° north of the Orion Nebula. The reflection nebula embedded in Sh2-279 is popularly known as the Running Man Nebula.
Sh2-155 is a diffuse nebula in the constellation Cepheus, within a larger nebula complex containing emission, reflection, and dark nebulosity. It is widely known as the Cave Nebula, though that name was applied earlier to Ced 201, a different nebula in Cepheus. Sh2-155 is an ionized H II region with ongoing star formation activity, at an estimated distance of 725 parsecs from Earth.
IC 405 is an emission and reflection nebula in the constellation Auriga north of the celestial equator, surrounding the bluish, irregular variable star AE Aurigae. It shines at magnitude +6.0. Its celestial coordinates are RA 05h 16.2m dec +34° 28′. It is located near the emission nebula IC 410, the open clusters M38 and M36, and the K-class star Iota Aurigae.
FU Orionis is a variable and binary star system in the constellation of Orion, that in 1937 rose in apparent visual magnitude from 16.5 to 9.6, and has since been around magnitude 9. The name FU Orionis is a variable star designation in the Argelander system, which are assigned sequentially as new variables are discovered. FU Orionis is about 1,360 light years distant and is associated with the molecular cloud Barnard 35.
25 Orionis, less commonly known by its Bayer designation Psi1 Orionis is a fifth-magnitude star in the constellation Orion. It lies among a dense cluster of low-mass pre-main-sequence stars in the Orion OB1a.
Pi6 Orionis (π6 Ori, π6 Orionis) is a solitary star in the eastern part of the constellation Orion. It is visible to the naked eye with an apparent visual magnitude of 4.469. Based upon an annual parallax shift of 3.45 mas, it is around 950 light-years from the Sun. At that distance, the visual magnitude of the star is reduced by an interstellar absorption factor of 0.52.
GW Orionis is a T Tauri type pre-main sequence hierarchical triple star system. It is associated with the Lambda Orionis star-forming region and has an extended circumtrinary protoplanetary disk.
Barnard 30 is a dark cloud in the Lambda Orionis ring, north of Lambda Orionis, also called Meissa. The region is about 1300 light years from Earth.
UX Orionis is a variable star in the constellation of Orion. It is a Herbig Ae star, located about 1000 light years from the Earth. At its brightest it is a magnitude 9.5 object, so it is too faint to be seen with the naked eye. UX Orionis is the prototype of the UX Orionis class of variable stars, which are young stellar objects that exhibit large, irregular changes in visual band brightness. UX Orionis was discovered by Henrietta Swan Leavitt.
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