Cepheus (constellation)
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Cepheus is a constellation in the deep northern sky, named after Cepheus, a king of Aethiopia in Greek mythology. It is one of the 48 constellations listed by the second century astronomer Ptolemy, and it remains one of the 88 constellations in the modern times.
The constellation's brightest star is Alderamin (Alpha Cephei), with an apparent magnitude of 2.5. Delta Cephei is the prototype of an important class of star known as a Cepheid variable. RW Cephei, an orange hypergiant, together with the red supergiants Mu Cephei, MY Cephei, VV Cephei, V381 Cephei, and V354 Cephei are among the largest stars known. In addition, Cepheus also has the hyperluminous quasar S5 0014+81, which hosts an ultramassive black hole in its core, reported at 40 billion solar masses, about 10,000 times more massive than the central black hole of the Milky Way, making this among the most massive black holes currently known.<ref name="Z1">Template:Cite journal This paper does acknowledge the possibility of an optical illusion that would cause an overestimation of the mass.</ref><ref name="G.Ghisellini, G.Ghirlanda">Template:Cite journal</ref>
History and mythologyEdit
Cepheus was the King of Aethiopia. He was married to Cassiopeia and was the father of Andromeda, both of whom are immortalized as modern day constellations along with Cepheus.<ref name="staal"/>
FeaturesEdit
Alderamin, also known as Alpha Cephei, is the brightest star in the constellation, with an apparent magnitude of 2.51.<ref>Template:Cite journal</ref> Gamma Cephei, also known as Errai, is the second-brightest star in the constellation, with an apparent magnitude of 3.21.<ref>Template:Cite journal</ref> It is a binary star, made up by an orange giant or subgiant<ref>Template:Cite journal</ref> and a red dwarf.<ref>Template:Cite journal</ref> The primary component hosts one exoplanet, Gamma Cephei Ab (Tadmor).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Delta Cephei is a yellow-hued supergiant star 980 light-years from Earth and the prototype of the class of the Cepheid variables. It was discovered to be variable by John Goodricke in 1784. It varies between 3.5m and 4.4m over a period of 5 days and 9 hours. The Cepheids are a class of pulsating variable stars; Delta Cephei has a minimum size of 40 solar diameters and a maximum size of 46 solar diameters. It is also a double star; the primary star also has a wide-set blue-hued companion of magnitude 6.3.Template:Sfn
There are four red supergiants in the constellation that are visible to the naked eye. Mu Cephei is also known as Herschel's Garnet Star due to its deep red colour. It is a semiregular variable star with a minimum magnitude of 5.1 and a maximum magnitude of 3.4. Its period is approximately 2 years.Template:Sfn The star's radius has been estimated to be from Template:Convert<ref>Template:Cite journal</ref> to Template:Convert.<ref name=":0">Template:Cite journal</ref> If it were placed at the center of the Solar System, it would likely extend past the orbit of Jupiter. The second, VV Cephei A, is a semiregular variable star, located approximately 5,000 light-years from Earth. It has a minimum magnitude of 5.4 and a maximum magnitude of 4.8,<ref name=":1">Template:Cite journal</ref> and is paired with a blue main sequence star called VV Cephei B. The red supergiant primary is around 1,050 times larger than the Sun.<ref>Template:Cite journal</ref> VV Cephei is also an unusually long-period eclipsing binary, but the eclipses, which occur every 20.3 years, are too faint to be observed with the unaided eye. The third, Zeta Cephei, is not as large as Mu Cephei and VV Cephei A with a diameter less than 200 times that of the Sun;<ref name=":2">Template:Cite journal</ref> however, its surface would lie between the orbits of Venus and Earth if placed at the center of the Solar System. Zeta Cephei has an apparent magnitude of 3.35,<ref name=":0" /> being the fourth-brightest star in the constellation. The last and faintest is V381 Cephei Aa with a maximum magnitude of 5.5.<ref name=":1" /> It is part of a triple star system similar to VV Cephei,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> and has a diameter 980 times that of the Sun.<ref>Template:Cite journal</ref> All four stars have initial masses more than eight times that of the Sun and are accepted core-collapse supernova candidates.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref>
Nu Cephei is a blue supergiant similar to Deneb with an initial mass of over 20 solar masses. It belongs to the Cepheus OB2 stellar association along with Mu Cephei and VV Cephei, which have similar initial masses.<ref>Template:Cite journal</ref>
There are several prominent double stars and binary stars in Cepheus. Omicron Cephei is a binary star with a period of 800 years. The system, 211 light-years from Earth, consists of an orange-hued giant primary of magnitude 4.9 and a secondary of magnitude 7.1. Xi Cephei is another binary star, 102 light-years from Earth, with a period of 4,000 years. It has a blue-white primary of magnitude 4.4 and a yellow secondary of magnitude 6.5.Template:Sfn
Krüger 60 is an 11th-magnitude binary star consisting of two red dwarfs. The star system is one of the nearest, being only 13 light-years away from Earth. It was once proposed as a possible home system for 2I/Borisov, the first accepted interstellar comet, but this was later rejected.<ref>Template:Cite arXiv</ref>
Deep-sky objectsEdit
- NGC 188 is an open cluster that has the distinction of being the closest open cluster to the north celestial pole, as well as one of the oldest-known open clusters.
- NGC 6946 is a spiral galaxy in which ten supernovae have been observed, more than in any other galaxy. It is sometimes called the Fireworks Galaxy.<ref>Template:Cite news</ref><ref>Template:Cite news</ref>
- IC 469 is another spiral galaxy, characterized by a compact nucleus, of oval shape, with perceptible side arms.
- The nebula NGC 7538 is home to the largest-yet-discovered protostar.<ref>Template:Cite journal</ref>
- NGC 7023 is a reflection nebula with an associated star cluster (Collinder 429); it has an overall magnitude of 7.7 and is 1,400 light-years from Earth. The nebula and cluster are located near Beta Cephei and T Cephei.Template:Sfn
- S 155, also known as the Cave Nebula,<ref name=Mobberley>Template:Cite book</ref> is a dim and very diffuse bright nebula within a larger nebula complex containing emission, reflection, and dark nebulosity.
- The quasar 6C B0014+8120 is one of the most powerful objects in the universe, powered by a supermassive black hole which is as massive as 40 billion Suns.<ref>Template:Cite journal 17:53:24 GMT.</ref>
VisualizationsEdit
Cepheus is most commonly depicted as holding his arms aloft, praying for the deities to spare the life of Andromeda. He also is depicted as a more regal monarch sitting on his throne.<ref name="staal">Template:Harvnb</ref>
EquivalentsEdit
In Chinese astronomy, the stars of the constellation Cepheus are found in two areas: the Purple Forbidden enclosure (紫微垣, Zǐ Wēi Yuán) and the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).
NamesakesEdit
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- USS Cepheus (AKA-18) and USS Cepheus (AK-265), United States Navy ships.
- Update 3.4 "Cepheus" of the videogame StellarisTemplate:Citation needed
See alsoEdit
ReferencesEdit
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- Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. Template:ISBN. Princeton University Press, Princeton. Template:ISBN.
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External linksEdit
- The Deep Photographic Guide to the Constellations: Cepheus
- The clickable Cepheus
- Star Tales – Cepheus
- Warburg Institute Iconographic Database (ca 160 medieval and early modern images of Cepheus)
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