Hydra (moon) the Hydra, the nine-headed serpent that battled Heracles in Greek mythology. The nine heads of Hydra are a reference to Pluto's tenure as the ninth planet; its initial, "H", refers to the Hubble Telescope, which discovered Hydra and, together with Nix, to the "New Horizons" mission whose safe passage was the motivation for taking the Hubble images. Hydra orbits the barycenter of the system in the same plane as Charon and Nix, at a distance of about 65,000 km. Its eccentricity of 0.0059 is small, but significantly non-zero, and the largest of those of Pluto's small moons (slightly larger than
Dictionary of Greek and Roman Biography and Mythology Dictionary of Greek and Roman Biography and Mythology The Dictionary of Greek and Roman Biography and Mythology (1849, originally published 1844 under a slightly different title) is an encyclopedia/biographical dictionary. Edited by William Smith, the dictionary spans three volumes and 3,700 pages. It is a classic work of 19th-century lexicography. The work is a companion to Smith's "Dictionary of Greek and Roman Antiquities" and "Dictionary of Greek and Roman Geography". The work lists thirty-five authors in addition to the editor, who is also an author for some definitions and articles. The authors were classical scholars, primarily from Oxford, Cambridge, Rugby