Visible at latitudes between +
90° and −
10°. Best visible at 21:00 (9 p.m.) during the month of November.
Cepheus is a
constellation in the far 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.
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.[4]
Alpha Cephei, also known as Alderamin, is the brightest star in the constellation, with an
apparent magnitude of 2.51.[5]Gamma Cephei, also known as Errai, is the second-brightest star in the constellation, with an apparent magnitude of 3.21.[6] It is a
binary star, made up by a
orange giant or
subgiant[7] and a
red dwarf.[8] The primary component hosts one exoplanet,
Gamma Cephei Ab (Tadmor).[9]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.[10]
There are three
red supergiants in the constellation that are visible to the naked eye.
Mu Cephei, also is 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.[11] The star is around 5.64
AU in radius. If it were placed at the center of the
Solar System, it would extend to the orbit of
Jupiter. 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, and is paired with a blue main sequence star called VV Cephei B. One of the largest stars in the galaxy, it has a diameter exceeding a thousand times that of the Sun.[11] 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 with a diameter only 94 times that of the Sun (comparable to the orbit of
Mercury),[12] and has an apparent magnitude of 3.35.[13]
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.[11]
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 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 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.[18]
S 155, also known as the Cave Nebula,[19] is a dim and very diffuse bright nebula within a larger nebula complex containing emission, reflection, and dark nebulosity.
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.[4]
^Ghisellini, G.; Ceca, R. Della; Volonteri, M.; Ghirlanda, G.; Tavecchi, F.; Foschini, L.; Tagliaferri, G.; Haardt, F.; Pareschi, G.; Grindlay, J. (2010). "Chasing the heaviest black holes in active galactic nuclei, the largest black hole". Monthly Notices of the Royal Astronomical Society. 405 (1): 387.
arXiv:0912.0001.
Bibcode:
2010MNRAS.405..387G.
doi:
10.1111/j.1365-2966.2010.16449.x.
S2CID40214759. This paper does acknowledge the possibility of an optical illusion that would cause an overestimation of the mass.
^Ghisellini, G.; Foschini, L.; Volonteri, M.; Ghirlanda, G.; Haardt, F.; Burlon, D.; Tavecchio, F.; et al. (14 July 2009). "The blazar S5 0014+813: a real or apparent monster?". Monthly Notices of the Royal Astronomical Society: Letters. v2. 399 (1): L24–L28.
arXiv:0906.0575.
Bibcode:
2009MNRAS.399L..24G.
doi:
10.1111/j.1745-3933.2009.00716.x.
S2CID14438667.
^Levesque, Emily M.; Massey, Philip; Olsen, K. A. G.; Plez, Bertrand; Josselin, Eric; Maeder, Andre; Meynet, Georges (August 2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought". The Astrophysical Journal. 628 (2): 973–985.
arXiv:astro-ph/0504337.
Bibcode:
2005ApJ...628..973L.
doi:
10.1086/430901.
ISSN0004-637X.
^"Smoky Shells". ESA/Hubble Picture of the Week. Retrieved 13 December 2012.
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,
ISBN0-939923-04-1