Argo Navis was a vast southern constellation of the classical sky, one of Ptolemy's forty-eight, representing the ship Argo in which Jason and the Argonauts sailed in quest of the Golden Fleece. So large and unwieldy was it that in the eighteenth century the astronomer Lacaille divided it into three separate constellations, Carina the keel, Puppis the stern, and Vela the sails, which are the forms recognised today; Argo itself is no longer an official constellation. Its brightest star, Canopus, second only to Sirius, lies in the keel. In astronomical tradition the old figure is a chapter of the sky's history rather than a current constellation or a zodiac sign. These are the features of Argo as the classical tradition described it before its division, distinct from any astrological use of the southern region it filled.
Beyond the formal 1750s division into Carina, Puppis and Vela, a fourth piece of the old ship was separated still earlier: Pyxis, the mariner's compass, was cut by Lacaille from stars near Argo's mast and given its own name distinct from the three larger pieces, so that the single classical ship left behind not three modern constellations but effectively four. Canopus, in the keel that is now Carina, was for centuries the southernmost bright star known to Mediterranean astronomers, and its heliacal rising was used as a calendar marker in ancient Egypt in a manner distinct from, and independent of, the more famous Sirius reckoning used for the Nile flood.