Constellations: Cetus 'the Whale' Content from the guide to life, the universe and everything

Constellations: Cetus 'the Whale'

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The tail fin of a humpback whale.
Have you gazed out on the ocean
Seen the breaching of a whale?
Have you watched the dolphins frolic in the foam?
Have you heard the song the humpback hears
Five hundred miles away?
Telling tales of ancient history of passages and home.

– 'I Want To Live' –  John Denver

The Constellation Cetus

Short form:Cet
Meaning:The Whale or Sea Monster
Area:1,231 sq deg
Co-ordinates1:Right Ascension 02h, Declination −10°

Cetus the whale (or 'sea monster') is a huge southern constellation; at 1,231 square degrees, it's the 4th-largest overall. Cetus is in the area of the sky known as 'the Sea' alongside other 'water' constellations. Bordering Cetus is Eridanus 'the river'; above it is Taurus, Aries and Pisces; and the other side is Aquarius. Beneath Cetus are Sculptor and Fornax.


The Roman historian Pliny claimed to have seen the 40' skeleton of a strange marine creature when it was brought to Rome. It was described as front part dog with a fish bottom half, a sort of 'canineplacoderm', or just a really ugly mermaid. This portmanteau is exactly how Cetus is depicted in John Flamsteed's Atlas Coelestis.


The vain queen Cassiopeia, wife of King Cepheus of Æthiopia, offended the god of the oceans, Poseidon, when she boasted that her beauty was greater than that of the sea nymphs, the Nereids, who were his handmaidens. Angry Poseidon sent storms to ravage the coast of their kingdom as punishment for the queen's vanity. To bring an end to the suffering, King Cepheus went to the Oracle for advice and was told to sacrifice his daughter Andromeda to the sea monster Cetus in order to placate Poseidon.

Andromeda was duly chained to the rocks on the coast2 for the sea monster to devour. She was saved at the last moment by the hero Perseus, riding in on Pegasus, his winged horse. Perseus turned Cetus to stone by forcing it to look at the head of the gorgon Medusa, who Perseus had recently slain. The sea monster was immortalised as a constellation by the great god Zeus.


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

The stars of Cetus don't quite follow the nomenclature rule; discounting variable star omicron Ceti, the brightest star of the constellation is beta Ceti, Deneb Kaitos, while several others are out of order.

The first variable star to be discovered was omicron Ceti, commonly named Mira (Latin meaning 'the amazing one'). It fluctuates between magnitude +10 and +1, making it one of the brightest periodic variables. Mira's strange behaviour pattern, including disappearing from view for part of its cycle, led astronomers to mistakenly assume it was a nova (exploding star). At the time of its scientific discovery in 1596, most people had a geocentric world-view (in which the Earth is at the centre of the universe and every other heavenly body revolves around it). To voice a different theory was considered heresy and many people died for their beliefs. The study of omicron Ceti added to the weight of evidence which eventually led towards the scientifically accepted heliocentrism.

Other interesting stars are: Tau Ceti which has a debris disc and is very close by at just 12 light years3 distant; Phi Ceti is a quadruple star system; another multiple is epsilon Ceti.

Star Table

StarDesignationName or
catalogue number
Brightness (m)Distance
(light years)
Spectral classification
and/or comments
ο Cetomicron CetiMira+1/+10 var420Red giant
β Cetbeta CetiDeneb Kaitos+2.0496Orange giant
α Cetalpha CetiMenkar+2.52220Red giant
γ Cetgamma CetiAl kaffaljidhma+2.782White giant
η Ceteta CetiDeneb Algenubi+3.45124Orange giant/has planets
τ Cettau Ceti52 Ceti+3.4912Has a debris disc
ι Cetiota CetiDeneb Kaitos Shemali+3.56290Orange giant
θ Cettheta CetiAltawk+3.6115Orange giant
ζ Cetzeta CetiBaten Kaitos+3.9260Binary star system
υ Cetupsilon CetiAbyssus Aqueus+3.99300Orange giant
δ Cetdelta CetiPhycochroma+4.08650Blue giant
π Cetpi CetiAl Sadr al Ketus+4.24442Blue-white giant
μ Cetmu Ceti87 Ceti+4.2784Yellow-white variable
ξ Cetxi Ceti65 Ceti+4.36360Binary star system
χ Cetchi Ceti53 Ceti+4.6677Binary star system
λ Cetlambda Ceti91 Ceti+4.6 var580Blue-white giant
σ Cetsigma Ceti76 Ceti+4.7484Yellow-white dwarf
φ Cetphi CetiAl Nitham+4.77210Quadruple star
ε Cetepsilon Ceti83 Ceti+4.8388Multiple star system
κ Cetkappa Ceti96 Ceti+4.8430Yellow dwarf
ν Cetnu Ceti78 Ceti+4.87372Double star system
ρ Cetrho Ceti72 Ceti+4.88528White giant
Luyten 726-8GCTP 343.10 A+BBL Ceti/UV Ceti+12 var8.8Binary star system

New General Catalogue (NGC)

The NGC was compiled by John Louis Emil Dreyer (the director of the Armagh Observatory from 1882 to 1916). The NGC objects in Cetus are a planetary nebula and two galaxies, one of which is included in the famous catalogue of Charles Messier.

NGC Table

CatalogueNameTypeBrightness (m)Distance
(light years)
NGC 246The Skull NebulaPlanetary nebula+10.81,600Exploded binary system star
NGC 247PGC 2758Galaxy+9.913mACW spiral
NGC 1068M77Galaxy+9.647mBarred spiral

Extrasolar Planets in Cetus

There have been many extrasolar planetary systems found in the constellation Cetus; the first was discovered in 2000; some stars have multiple orbiting planets. 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
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
94 Cet A94 Cet A b1.75352000Binary star system
79 Cet79 Cet b0.2675.52000Hot sub-Saturn
HD 11506HD 11506 b4.71,4502007Superjovian
HD 11506HD 11506 c0.81702009Gas giant
HD 5319HD 5319 b1.946692007Superjovian
HD 224693HD 224693 b0.7272006Hot subjovian
HD 2638HD 2638 b0.483.442005Hot subjovian
HD 11964HD 11964 b0.62,1102007Gas giant
HD 11964HD 11964 c0.1382005Hot Neptune
81 Cet81 Cet b5.39522008Superjovian
BD-17°63BD-17°63 b5.16552008Superjovian
HIP 12961HIP 12961 b0.47572009Hot gas giant
HD 6718HD 6718 b1.652,4962009Superjovian
HD 1461HD 1461 b0.0245.772009Hot super-Earth
HD 1461HD 1461 c0.01813.52011Hot super-Earth
HD 1461HD 1461 d0.35,0002009Gas giant
HD 1461HD 1461 e0.0724542009Super-Earth
HIP 5158HIP 5158 b1.43462009Habitable zone
HIP 5158HIP 5158 c159,0182010Brown dwarf
HD 1690HD 1690 b6.15332010Superjovian
WASP-26WASP-26 b1.022.752010Hot Jupiter
WASP-20WASP-20 b0.34.92011Hot gas giant
WASP-44WASP-44 b0.82.422011Hot Jupiter
HD 7449HD 7449 b1.11,2752011Sun-like star
HD 7449HD 7449 c24,0462011Superjovian
HIP 11952HIP 11952 b2.93290201212.8 billion years old
HIP 11952HIP 11952 c0.786.952012Oldest exoplanet system/
discovered (up to 2012)
HD 4732HD 4732 b2.373602012Superjovian
HD 4732HD 4732 c2.372,7322012Superjovian/habitable zone
75 Cet75 Ceti b36922012Superjovian
WASP-71WASP-71 b2.262.92012Hot Jupiter
WASP-75WASP-75 b1.072.482012Hot Jupiter
WASP-77AWASP-77A b1.761.362012Hot Jupiter
HAT-P-45HAT-P-45 b0.93.132013Hot gas giant
HAT-P-46HAT-P-46 b0.54.52013Hot gas giant
HAT-P-46HAT-P-46 c2782013Hot superjovian
η Ceteta Ceti b2.464072014Superjovian
η Ceteta Ceti c3.27442014Superjovian
HD 1666HD 1666 b6.42702015Superjovian
HD 4747HD 4747 b6013,8362016Brown dwarf
HD 9174HD 9174 b1.11,1792016Sun-like star
WASP-136WASP-136 b1.55.22016Hot Jupiter
WASP-138WASP-138 b1.23.632016Hot Jupiter

The star Tau Ceti hosts five planets, discovered in December 2012. They are thought to be rocky worlds so are compared with Earth's mass. One of them, Tau Ceti e, may reside in the system's habitable zone.

Tau Ceti

catalogue number
Planet mass
(Earth scale)
Orbital period
(Earth days)
Tau Ceti b2.014Hot super-Earth
Tau Ceti c3.135.3Hot super-Earth
Tau Ceti d3.594Super-Earth
Tau Ceti e4.3168Super-Earth
Tau Ceti f6.7642Super-Earth

Whales in Modern Culture

  • A sperm whale, created by the Infinite Improbability Drive, had a brief appearance in the Hitchhiker's Guide to the Galaxy by Douglas Adams.
  • According to the King James version of The Bible, Jonah was swallowed by a whale, but vomited back out again after God spared Jonah's life.
  • When NASA discovered that sperm whale oil did not freeze in outer space, they used it as a lubricant in the vehicles of their space programme, including the ROV (Remotely Operated Vehicle) for expeditions to the Moon and Mars, where the surface temperature is extremely cold indeed. The discovery was so significant that Sir Patrick Moore devoted a whole programme of The Sky At Night to talk about the implications, and invited marine biologists and cetacean experts to join the discussion.
  • The novel Moby-Dick was written in 1851 by Herman Melville. The story is about a ship's captain who becomes obsessed with hunting a whale, Moby-Dick, who the captain blames for the loss of his leg on a previous whaling expedition. The battle between the hunter and the hunted is to the death, but the tale itself has come to symbolise the fight within, and the choice we all have, when to let go.
  • A town on the southern coast of France is named Sète and a whale appears as a visual pun in the town's coat of arms. The name derives from a fairly ancient way of using 'set' to mean 'mountain', but the name was spelled 'Cette' after the 17th Century - hence the whale connection. The spelling was changed after 1936, but the whale remains on the coat of arms.

Cetus in Science Fiction

In Star Trek TOS, villain Khan Noonian Singh and his followers were imprisoned on the 5th planet from Alpha Ceti, which was named as Alpha Ceti V. Pirates hid on a planet orbiting Mira (omicron Ceti) in A Relic Of The Empire by Larry Niven. There's a wormhole connecting Earth and UV Ceti in Timemaster by Robert Lull Forward (1932 - 2002). To list the references to Tau Ceti in the science fiction genre would require an Entry all on its own, so suffice to say it's a popular star!

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2This scene inspired artists such as Paul Gustav Doré.3A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.

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