Cepheus (constellation)

Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations. Its brightest star is Alpha Cephei with an apparent magnitude of 3.5. 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, VV Cephei and V354 Cephei are among the largest stars known. In addition, Cepheus also has the hyperluminous quasar S5 0014+81, hosting an ultramassive black hole in its core at 40 billion solar masses, about 10,000 times more massive than the central black hole of the Milky Way, making it the most massive black hole known in the universe.

History and mythology

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.^[2]

Notable features

The constellation Cepheus as it can be seen by the naked eye.

Delta Cephei is the prototype Cepheid variable, a yellow-hued supergiant star 980 light-years from Earth. It was discovered to be variable by John Goodricke in 1784. It varies between 3.5^m and 4.4^m 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 yellow star also has a wide-set blue-hued companion of magnitude 6.3.^[3]

There are several other prominent variable stars in Cepheus. One, μ 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.^[4] The star is around 11.8 AU in radius. If it were placed at the center of the Solar System, it would extend to the orbit of Saturn. Another, VV Cephei A, like Mu Cephei, is a red supergiant and a semiregular variable star, located at least 5,000 light-years from Earth. It has a minimum magnitude of 5.4 and a maximum magnitude of 4.8. One of the largest stars in the galaxy, it has a diameter of 1,300 solar diameters. 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. T Cephei, also a red giant, is a Mira variable with a minimum magnitude of 11.3 and a maximum magnitude of 5.2, 685 light-years from Earth. It has a period of 13 months and a diameter of 500 solar diameters.^[4]

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 4000 years. It has a blue-white primary of magnitude 4.4 and a yellow secondary of magnitude 6.5.^[4]

Kruger 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.

Deep-sky objects

NGC 7354 is a planetary nebula located in the constellation Cepheus.^[5]

• 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.
• The Fireworks Galaxy (NGC 6946) is a spiral galaxy in which nine supernovae have been observed, more than in any other galaxy.
• 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.
• NGC 7023 is a reflection nebula with an associated star cluster (Collinder 429); it has an overall magnitude of 7.7 and is 1400 light-years from Earth. The nebula and cluster are located near Beta Cephei and T Cephei.^[6]
• The quasar 6C B0014+8120 is one of the most powerful objects in the universe, powered by a supermassive black hole equivalent to 40 billion Suns.

Visualizations

Cepheus as depicted in Urania's Mirror, a set of constellation cards published in London c. 1825.

Cepheus is most commonly depicted as holding his arms aloft, praying for the gods to spare the life of Andromeda. He is also depicted as a more regal monarch sitting on his throne.^[2]

Equivalents

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).

In popular culture

• In the TV sitcom 3rd Rock from the Sun, the aliens' home planet is stated to be located in a barred spiral galaxy on the Cepheus-Draco border.
• The performer Deadmau5 named his song, "HR 8938 Cephei" after a star in the constellation.

Namesakes

• USS Cepheus (AKA-18) and USS Cepheus (AK-265), United States navy ships.

See also

• Cepheus (Chinese astronomy)

References

• Levy, David H. (2005). Deep Sky Objects. Prometheus Books. ISBN 1-59102-361-0. 
• Ridpath, Ian; Tirion, Wil (2001), Stars and Planets Guide, Princeton University Press, ISBN 0-691-08913-2 
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0-00-725120-9. Princeton University Press, Princeton. ISBN 978-0-691-13556-4.
• Staal, Julius D.W. (1988), The New Patterns in the Sky: Myths and Legends of the Stars (2nd ed.), The McDonald and Woodward Publishing Company, ISBN 0-939923-04-1 

External links

Wikimedia Commons has media related to: Cepheus (category)

• The Deep Photographic Guide to the Constellations: Cepheus
• Star Tales – Cepheus
• Cepheus Constellation at Constellation Guide
• Warburg Institute Iconographic Database (over 150 medieval and early modern images of Cepheus)

Coordinates: 22^h 00^m 00^s, +70° 00′ 00″