Cetus: A Greek Astronomical Sea Monster

Cetus is the infamous monster from ancient Greek mythology, often depicted as a giant sea creature or a sea serpent. The most popular story about Cetus is closely associated with the myth of Perseus and Andromeda.

Who or What Was Cetus?

Cetus was a sea monster in ancient Greek mythology, often depicted as a giant sea serpent that embodies the dangers of the sea.

Cetus is most famously associated with the story of Perseus and Andromeda. In this tale, Cetus is sent by the sea god Poseidon to ravage the kingdom of Ethiopia as punishment. To appease the monster, the king and queen of Ethiopia offer their daughter, Princess Andromeda, as a sacrifice. Andromeda is chained to a rock by the seashore, waiting to be devoured by Cetus.

The hero Perseus, on his journey back from defeating the Gorgon Medusa, comes across Andromeda and Cetus. Using Medusa’s severed head, Perseus turns Cetus into stone, saving Andromeda and the kingdom.

As a representation of the perils and mysteries of the sea Cetus’ appearance in myths serves as a way to emphasize the bravery and resourcefulness of the heroes who face and overcome such challenges.

Cetea: The Sea Monsters of the Greeks

In Greek mythology, the general name which was used to refer to sea monsters was Cetea. Usually, they were depicted as gigantic, serpentine-like creatures with rows of sharp teeth. But, they would also be shown with features that we normally see with land creatures, like rabbit ears or antlers.

Why were they important in mythology? Well, mostly because they served the sea gods. There are plenty of sea gods, but the monsters would particularly be of great use to Poseidon.

Normally it is believed that they were pretty tolerant towards the gods and nymphs of the sea, but once in a while, they got their occasional tantrum. Even towards their owners.

Personifying Natural Phenomena

Recent research suggests that the myths surrounding the attacks of Cetea find their roots in tsunamis or earthquakes in a particular region.

They believe that natural disasters with severe consequences would be a topic of conversation for a long time. But, after a while these stories get adjusted, accumulating to a whole different story. This way, it is possible that the Greeks believed that tsunamis or earthquakes were actually caused by the Cetea.

Cetus: More Than One Monster?

One of the most prominent stories about a Cetea is the one about Cetus. But, it’s a bit contested what Cetus actually refers to. The term cetus can also be seen as the singular form of Cetea, so a single sea monster.

Indeed, cetus was used to refer to nearly any large sea creature. Well, maybe not any. Mostly the ones that had the same characteristics as whales or sharks.

For example, they were believed to have broad, flat tails, lifting their head above the surface to inspect any ship that was passing. Also, mourning sounds were often characteristic of a cetus. Both the tail and the sounds are, of course, also characteristics of whales.

What is the Myth of Cetus?

So cetus can refer to any whale or shark. However, the most intriguing myth is the one when Poseidon sent one specific cetus to wreak havoc on the kingdom of Aethiopia: modern-day Ethiopia.

Terrorizing Ethiopia

The victims of the myth of Cetus were located in Ethiopia. Poseidon was mad at one of its rulers since he thought that their queen was too reckless with her words. She stated that she and her daughter, princess Andromeda, were more beautiful than any of the Nereids, sea nymphs (often accompanying Poseidon and they also appear in the story of Jason and the Argonauts).

Queen Cassiopeia probably wasn’t fully aware of their importance, or at least not the reaction it would generate in Poseidon. Indeed, he sent Cetus to bring across a message.


A devastating attack would follow for the kingdom of Cassipeia’s man, King Cepheus. In order to save his kingdom, he consulted a wise oracle. An oracle, in this sense, is basically a medium through whom advice or prophecy was sought from the gods.

READ MORE: The Oracle of Delphi: The Ancient Greek Fortuneteller

Sacrificing Andromeda 

The outcome of the oracle wasn’t all that happy, unfortunately. The prophecy was that King Cepheus and Queen Cassiopeia had to sacrifice their daughter Andromeda to Cetus. Only then, the attack would stop.

Yet, they made up their mind pretty easily. The princess was quickly chained to an ocean cliff. Dinner served, war solved.

Death of Cetus

As soon as Cetus tried to devour Andromeda, Perseus flew by. Zeus’ son just returned from a victory over Medusa.

Perseus saw the princess and immediately fell in love with her. Conveniently, he was carrying the head of Medusa when he flew by. So Perseus flew down to save Andromeda, just when Cetus was rising from the water to attack.

READ MORE: Who Invented Water? History of the Water Molecule

In the most common variation, Perseus exposed the head to Cetus, turning it into stone. But, in another variation, he didn’t bring the head. Instead, Zeus‘ son stabbed Cetus with his sword and killed it. Although there is a bit of variation in this regard, the end result stays the same.

Constellation Cetus

Cetus is not only known as a monster, but it might actually be even more famous for it being a constellation of stars. It was first mentioned by the Greek astronomer Ptolemy. He was of great influence in many different fields, including astronomy.

The names he would come up with were based on the mythological figures of ancient Greece. This specific constellation was given the name Cetus since it looked like a whale, at least according to Ptolemy.

At What Time of the Year is Cetus Visible?

The constellation Cetus can be seen in the northern hemisphere somewhere in the late fall and early winter. It is visible at latitudes between 70 degrees and -90 degrees.

A large distance indeed, which is mainly due to the fact that it is a very large constellation. The fourth largest of all, in fact. Since whales are also known as the largest animals on earth, this should come as no surprise.

The constellation Cetus lies in the middle of a part of the sky that is recognized as ‘The Sea’ by mythologists. It contains some other water-related constellations apart from Cetus, namely Eridanus, Pisces, Piscis Austrinus, and Aquarius.

In the constellation Cetus, Beta Ceti is the brightest star. It is an orange giant that is located about 96 light-years away. From Earth, it is perceived as the brightest star exactly because it is relatively close to Earth. Beta Ceti is, and was, also recognized by Arabic astronomers as ‘the second frog’. Maybe a bit less frightening than how the Greeks saw it.

Another notable star is Menkar (Alpha Ceti), a red giant star located 220 light-years from Earth. Alpha is, in theory, more shiny than the Beta Ceti. But, because it is located around 124 light-years further away (that is, 124 times 5.88 trillion miles), we don’t perceive it as bright as it actually is.

Another important star goes by the name of Omicron Ceti, or wonderful star. It got this nickname because the star has quite unusual fluctuations.

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