Intro and Visual description
Hydra the Water Snake is included in the ancient star catalogs of Eudoxos of Knidos, Aratos of Soli, and Ptolemy. It is the largest and longest of the constellations, stretching from Cancer to Libra.
Its brightest star is Alphard, which has an orangish tint. Several constellations and asterisms ride on its back; from head to tail they are Sextans the Sextant, Crater the Cup, Corvus the Crow, and Noctua the Owl.
M48 (Galactic cluster), mag. 6.0.
M68 (Globular cluster), mag. 8.2.
M83 the Pinwheel Galaxy (Spiral galaxy), mag. 7.6.