Cetus constellation from Johannes Hevelius' Prodromus astronomiae, Firmamentum Sobiescianum, sive Uranographia, 1687. Cetus is one of the 48 constellations described by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations defined by the International Astronomical Union. Its name refers to Cetus, a sea monster in Greek mythology. Cetus may have originally been associated with a whale, which would have had mythic status amongst Mesopotamian cultures. It is often now called the Whale, though it is most strongly associated with Cetus the sea monster, who was slain by Perseus as he saved the princess Andromeda from Poseidon's wrath. The Hevelius Firmamentum was the first star atlas to rival Bayer's Uranometria in accuracy, utility, innovation, and influence. Hevelius was perhaps the most active observational astronomer of the last half of the seventeenth century. His star atlas is notable for many reasons. It contains 56 large, double page engraved star maps. The star positions for the charts were derived from his own star catalog, based on his own observations, which was first published along with the atlas. It is unique among the Grand Atlases in choosing to depict the constellations as they would appear on a globe, that is, from the outside looking in, rather than from a geocentric point of view, as Bayer and most others adopted.