Whales : a feast for the eyes!

The whale is present in the sky in two forms: a constellation and a dwarf galaxy!

Situated below the constellation Aquarius, the Whale (Cetus) is the fourth largest constellation in the sky. In ancient times its name refers to the sea monster sent by Poseidon to destroy all forms of life. Greek mythology tells that the god of the sea wanted to take revenge on Cassiopeia, who was bold enough to declare that her daughter was more beautiful than Poseidon's wife. Later in the Middle Ages, Christian astronomers saw the whale that swallowed Jonah in an episode told in the Bible.

Situated near the constellation of Cetus (the whale), the Cetus Dwarf galaxy is part of our local group consisting of about 40 galaxies including ours. It lies approximately 2.46 Million light-years from Earth and has a very low surface brightness. This Cetus dwarf galaxy was discovered very recently, in 1999, by Alan Whiting, George Hau and Mike Irwin.

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The Cetus constellation is very large, but has few bright stars, and its shape is not easy to draw.

Initially, the "sea monster" was depicted as a kind of large squid armed with a beak (α Cet) and large tentacles (ß Cet).

Today the sea monster has become a whale and its representation is reversed : α marks the tail of the whale, and ß her mouth, but in both cases, this form is not very evocative.

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Cetus Dwarf is a dwarf spheroidal galaxy. We classify a galaxy as a dwarf spheroidal one if its stars have a more or less spherical and small distribution, i.e made of a few million to several hundred million stars. All the stars that can be now observed in the galaxy, are red giants ; the equivalent of what would become of our sun after billions of years when hydrogen has been completely burned in its core.

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