Cetus (a name from Greek mythology, referring to a 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 primordial cosmic female principle, the sea-monster Tiamat.

In Greek mythology, together with the constellations above it, of Andromeda, Cepheus, Perseus, Cassiopeia, and possibly Pegasus), this may be the source of the myth of the Boast of Cassiopeia, with which it is usually identified.

In certain earlier Greek mythology, it also represented the gates (and gateposts) of the underworld (considered to be the area under the ecliptic). As such, together with other features in the Zodiac sign of Pisces (including Pisces itself, as well as prominent stars behind Cetus), it may have formed the basis of the myth of the capture of Cerberus in The Twelve Labours of Herakles.