Hercules is a large northern constellation, one of Ptolemy's forty-eight, representing the greatest of the Greek heroes, though anciently it was known simply as the Kneeler, a figure kneeling with one foot raised, before it was firmly identified with Heracles. It has no first-magnitude stars, but its central four stars form a distinctive shape called the Keystone, and within it lies the Great Globular Cluster of Hercules, one of the finest such clusters in the northern sky. The hero is shown amid the sites of his labours, near the dragon Draco and the constellations he overcame. In astronomical tradition the constellation is a pattern of stars rather than a zodiac sign. These are the features of Hercules as the classical and modern traditions describe it, distinct from any astrological reading of the sky it occupies.
Between Hercules and Cygnus, Hevelius in 1687 introduced Vulpecula, the little fox, originally depicted grasping a goose in its jaws; the goose was later dropped from the figure, leaving only the fox, a reminder that even the officially adopted modern constellations were not always fixed in their final form on first introduction. The absence of any first-magnitude star has not diminished Hercules's importance to observers, since its globular cluster, catalogued by Messier as M13, is among the finest deep-sky objects visible from northern latitudes and was the target of the famous 1974 Arecibo radio message aimed at any potential audience among the stars.