Cetus

Cetus (the Whale or Sea Monster) is a constellation of the southern sky, in the region known as the Water[?], near other watery constellations like Aquarius, Pisces, and Eridanus.

Notable features This constellation's most notable star is Mira, ο Ceti, the first variable star to be discovered. Over a period of 331.65 days it varies from magnitude 2.0, one of the brightest in the sky and easily visible to the unaided eye, to 10.1 and back again. Its discovery in 1596 by David Fabricius further dented the unchangeability of the heavens and lent support to the Copernican revolution[?].

Other stars in the constellation include the α star, Menkar; the β star, Deneb Kaitos, brightest in the constellation; and τ Ceti, the 17th closest star to Earth.

The ecliptic passes very close to the constellation. Some of the planets can be in this constellation for brief periods of time. The asteroid 4 Vesta was discovered in this constellation in 1827.

Notable deep sky objects Cetus lies far from the galactic plane, so many distant galaxies are visible, unobscured by dust from the Milky Way. Of these, the brightest is M77, a 9th-magnitude spiral galaxy near δ Ceti.

History and Mythology This constellation has been known since antiquity. In Mesopotamia, it was identified with the cosmic dragon Tiamat. In classical mythology, it was the sea monster to whom the irritated Poseidon demanded that the princess Andromeda be sacrificed. The hero Perseus saved the princess by turning the monster to stone with the head of Medusa.