SAGITTA, in Astronomy, the Arrow, a constellation of the northern hemisphere, near the Eagle, and one of the forty-eight old asterisms. According to the fabulous ideas of the Greeks, this constellation owes its origin to one of the arrows of Hercules, with which he killed the eagle or vulture that gnawed the liver of Prometheus. In the catalogues of Ptolemy, Tycho, and Hevelius, the stars of this constellation are only five in number, while Flamsteed made them amount to eighteen.