Argo

Argo's own article covers its eighteenth-century division into Carina, Puppis and Vela in detail. Set aside from that later history, the whole ship also belonged, for as long as it existed as a single figure, to a much older grouping that had nothing to do with Jason's quest at all.

The stretch of sky running from Aquarius and Capricornus through Piscis Austrinus, Eridanus, Delphinus and Equuleus carries a persistent watery theme older than Greek myth-making, inherited by Greek astronomers from Babylonian sky-lore because the Sun crossed this region during the ancient Near East's rainy season. A ship afloat in a sea is the most literal possible member of that theme: unlike Equuleus, whose presence here looks incidental, Argo's presence is thematically exact, a vessel placed in precisely the stretch of sky already read as an ocean before anyone had attached the Argonauts to it.

Historians of astronomy label this loose cluster the Heavenly Waters, a modern convenience rather than a boundary Ptolemy drew in the Almagest, where his forty-eight are sorted only into zodiacal, northern and southern lists with no named thematic groups at all.

Argo was, by size alone, the largest single member the ancient sea ever held, and its eventual division was as much a practical response to an unmanageable figure as it was the end of a ship that had, for a very long time, simply been floating where a ship belonged.

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.