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
Greek mythology libretti for many of Handel's and Mozart's operas. By the end of the 18th century, Romanticism initiated a surge of enthusiasm for all things Greek, including Greek mythology. In Britain, new translations of Greek tragedies and Homer inspired contemporary poets (such as Alfred Lord Tennyson, Keats, Byron and Shelley) and painters (such as Lord Leighton and Lawrence Alma-Tadema). Christoph Gluck, Richard Strauss, Jacques Offenbach and many others set Greek mythological themes to music. American authors of the 19th century, such as Thomas Bulfinch and Nathaniel Hawthorne, held that the study of the classical myths was essential to the understanding of