Constellations: Cepheus 'the King' Content from the guide to life, the universe and everything

Constellations: Cepheus 'the King'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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The constellation Cepheus 'the King'.
Name:Cepheus
Genitive:Cephei
Short form:Cep
Area:588 sq deg
Co-ordinates1:Right Ascension 22h, Declination +70°
Origin:Ancient

Cepheus the Constellation

The northern constellation Cepheus features in the 48 constellations originally listed by the Greek astronomer Ptolemy (c90 - 168 AD), and is one of the 88 internationally recognised modern constellations. If you were to draw a line between the main stars, you'd end up with a house-shape, complete with roof and a little garden path. The top part of Cepheus covers about a quarter of the circumpolar region, adjoining Ursa Minor and Camelopardalis. Cepheus is further bordered by his queen, the vain Cassiopeia, and Draco, the dragon constellation. Cygnus and Lacerta are immediately underneath Cepheus.

Cepheus has some interesting deep-space objects; one which definitely has the wow-factor is the brilliant Fireworks Galaxy aka NGC 6946, a clockwise spiral galaxy which spans about 20,000 light years2. Another gem is emission nebula IC 1396 which contains the enigmatic and mysterious Elephant Trunk Nebula.

Mythology

King Cepheus was the ruler of Æthiopia. His vain wife, Queen Cassiopeia, boasted that she was more beautiful than the Nereids (sea-nymphs), who were the handmaidens of the sea god Poseidon. The angry god bombarded their kingdom with ferocious storms and forbade the Nereids from rescuing sailors in the Red Sea, so they all perished. King Cepheus sought the advice of the Oracle, discovering to his horror that the only way to appease Poseidon was to sacrifice their only daughter Andromeda to Cetus, a sea monster. Heartbroken, the king did as he was asked and Andromeda was chained naked to a rock3 to await her fate.

Luckily for her, Perseus rode by on Pegasus, the winged horse. He made a pact with King Cepheus that if he disposed of Cetus, in exchange he would be given the hand of the fair maiden Andromeda in marriage. Perseus turned Cetus to stone by holding aloft the head of the gorgon, which he had just slain.

When Perseus tried to claim his reward, Cepheus and Cassiopeia attempted to back out of the deal by claiming Andromeda was already betrothed to someone else. Undiscouraged, Perseus eloped with Andromeda and they had many children; their descendants founded the Persian race. Perseus and Andromeda were the ancestors of demigod Hercules, who also earned his own constellation.

Stars

The scientific star names are simple to understand (if you know your Greek alphabet). For example: 'alpha Cephei' means that it is the brightest star in the constellation Cepheus. The next brightest is designated 'beta', etc. This is known as the 'Bayer designation'. Some stars have proper names as well; for example, alpha Cephei is Alderamin. Others are known by their catalogue number.

Delta Cephei, discovered to be variable by John Goodricke in 1784, is a prototype for what are now called Cepheid variable stars. The study of stars such as these helps astronomers determine distance.

On the scale of largest-known stars, Cepheus boasts three in the top five! Mu Cephei is known as Herschel's Garnet Star and also Garnet Sidus. It is a red supergiant and one of the largest stars known to us. Only four more stars are larger than mu Cephei, and two of those are in the same constellation: VV Cephei A and V354 Cephei. V354 Cephei is the third-largest star known; if it existed in our solar system, its girth at 7AU (astronomical units) would reach from the position of the Sun to beyond the orbit of Jupiter. VV Cephei A is the big daddy, though; at almost 2,000 times the mass of our Sun, it is the biggest star ever measured (it would swallow up Saturn).

Gamma Cephei is a binary star system and gamma Cephei A has a planet, gamma Cephei Ab.

Kappa, omicron and pi Cephei are triple star systems.

Nu Cephei has the common name Cor Regis which is Latin for 'heart of the king', a deserved romantic-sounding name for the wonderful multiple star system. At 5th magnitude it's hard to spot with the naked eye but is a visual treat in binoculars.

Star Table

StarDesignationName or
catalogue number
MagnitudeDistance
(light years)
Spectral classification
and/or comments
α Cepalpha CepAlderamin+2.45 var49White subgiant
β Cepbeta CepAlfirk+3.2 var600Blue-white giant
γ Cepgamma CepAlrai+3.2 var45Planetary system
δ Cepdelta CepCepheidus Prototypus+3.8 var890Prototype: Cepheid variables
ε Cepepsilon CepPhicares+4.1 var85Yellow-white dwarf
ζ Cepzeta CepTsao Fu+3.4 var720Orange subgiant
η Cepeta CepAl Agemim+3.4 var45Orange giant
θ Ceptheta CepAl Kidr+4.2 var136Binary star system
ι Cepiota CepAlvahet+3.5 var115Orange giant
κ Cepkappa Cep1 Cephei+4.38327Triple star system
λ Ceplambda Cep22 Cephei+5.051,600Blue giant
μ Cepmu CepHerschel's Garnet Star+4.045,000Red supergiant
ν Cepnu CepCor Regis+4.25 var5,100Multiple star system
ξ Cepxi CepAlkurah+4.3100Binary star system
ο Cepomicron Cep34 Cephei+4.7210Triple star system
π Ceppi Cep33 Cephei+4.4220Triple star system
VV Cephei AHD 208816HR8383+4.9 var3,000Red hypergiant
V354 Cephei+5.6 var9,000Red hypergiant

New General Catalogue (NGC)

The NGC was compiled by John Louis Emil Dreyer (the director of the Armagh Observatory from 1882 to 1916). NGC 7380, aka the Wizard Nebula covers an area measuring 100 light years and lies some 8,000 light years distant. NGC 7354 is a planetary nebula which has striking red jets.

Since the NGC catalogue was compiled, improved detection methods have uncovered other wondrous sights which are registered as IC (Index Catalogue); Sh (the Sharpless Catalogue); or the Caldwell Catalogue which was compiled by Sir Patrick Moore. All the following appear in the Caldwell Catalogue:

Caldwell Catalogue

CatalogueNameTypeMagnitudeDistance
(light years)
Remarks
Caldwell 1NGC 188Open star cluster+8.14,800Less than 5° from
North Celestial Pole
Caldwell 2NGC 40Planetary nebula+11.63,500Measures one light year diameter
Caldwell 4NGC 7023Reflection nebula+6.81,300Iris Nebula
Caldwell 9Sh2-155Emission nebula+7.72,800Cave Nebula
Caldwell 12NGC 6946CW spiral galaxy+9.710 millionFireworks Galaxy

Extrasolar Planets in Cepheus

There has been one extrasolar planetary system found in the constellation Cepheus up to 2007. It orbits a binary star, Alrai (gamma Cephei A), and was discovered in 1988. Alrai is an orange sub-giant star, therefore the habitable zone is wider than that of our own Solar System. Because planet gamma Cephei A b orbits Alrai at 2 AU (astronomical units4) it is therefore deemed to be within the fabled 'Goldilocks Zone' (the range for water in its liquid form). The planet is a gas giant, which deems life (as we know it) improbable, however the gas giants of our Solar System have many moons which could be capable of supporting life if they had sufficient mass to hold an atmosphere and inhabited the 'Goldilocks Zone'. Technology needs to advance some way before we can begin detecting moons around extrasolar planets though.

Figures given in the table below are the length of the planet's orbital period around its parent star, which we know of as a year. The mass of the extrasolar planet is compared to that of Jupiter, our Solar System's largest planet, known by astronomers as the 'Jovian scale'.

Extrasolar Planets Table

Star name or
catalogue number
Planet
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
Alraigamma Cephei A b1.69031988First detected extrasolar planet

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (-) for southern ones.2A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.3This scene inspired artists such as Théodore Chassériau.4An astronomical unit is the average distance between Earth and the Sun, 93 million miles or 150 million km.

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