Cancer constellation from Johannes Hevelius' Prodromus astronomiae, Firmamentum Sobiescianum, sive Uranographia, 1687. Hevelius' star atlas 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. Cancer 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. Cancer is the fourth astrological sign in the Zodiac, which is associated with the constellation Cancer.