CETUS ("The Whale"), in astronomy, a constellation of the southern hemisphere, fabled by the Greeks to be the monster sent by Neptune to devour Andromeda, but which was slain by Perseus. It contains the long-period variable star Mira Ceti (o Ceti), which was the first star recognized to be variable (by Fabricius in 1596). It usually ranges from the ninth to the third magnitude in about 34o days; but this kind of vari ation is always rather irregular. It has recently been found to have a companion distant rather less than a second of arc. The com panion was first suspected from spectroscopic observations; when looked for visually it was easily seen, but it is difficult to under stand why it had escaped notice in a star which was so continually studied. The companion is itself a very interesting star, possess ing an unusual type of spectrum with bright lines ; it is probably a "white dwarf," like the companion of Sirius. (A. S. E.)