in Astronomy, the whale; a large constellation of the southern hemisphere, under Piscis, and next the water of Aquarius. The stars in the constellation Cetus, in Ptolemy's catalogue, are twenty-two; in Tycho's twenty-one; in Hevelius's forty-five; in the Britannic catalogue ninety-seven.

Cetus is represented by the poets as the sea-monster which Neptune, at the suit of the nymphs, sent to devour Andromeda for the pride of her mother, and which was killed by Perseus. In the mandible of Cetus is a variable star which appears and disappears periodically, passing through the several degrees of magnitude, both increasing and diminishing, in about 333 days. See ASTRONOMY.