- Aratus applied the mythical name Ἠριδανός (Eridanos) to this constellation although many other authorities, including Ptolemy in the Almagest, simply called it Ποταμός (Potamos), meaning river. Eratosthenes had another identification: he said that the constellation represented the Nile, ‘the only river which runs from south to north’. Hyginus agreed, claiming that the star Canopus lay at the end of the celestial river, in the same way that the island Canopus lies at the mouth of the Nile. However, in this he was wrong, for Canopus marks a steering oar of the ship Argo and is not part of the river. Hyginus had evidently misunderstood a comment by Eratosthenes, who had simply said that Canopus lay ‘beneath’ the river, meaning that it was at a more southerly declination.