Eridanus, the Celestial River

Eridanus is a long, winding southern constellation, one of Ptolemy's original forty-eight, that meanders across the sky like a river from near Orion's foot far to the south. The Greeks identified it with a great river, sometimes the Po or the Nile, and connected it with the myth of Phaethon, who lost control of the sun-chariot and fell blazing into the river Eridanus. Its brightest star, Achernar, marks the river's end deep in the southern sky. As one of the longest constellations, it threads among several others. In astronomical tradition the constellation is a pattern of stars rather than an astrological sign; its watery identity places it among the group of constellations associated with water. These are the features of Eridanus as the classical and modern traditions describe it, distinct from any astrological use of the region of sky it occupies.

The stretch of southern sky below Eridanus and Cetus was largely blank to Ptolemy, who charted the classical world's visible horizon and no further; Lacaille filled the gap in the 1750s with Fornax, the furnace, and Sculptor, the sculptor's studio, both named for instruments of Enlightenment learning rather than for any figure out of myth, a naming style that marks the modern constellations off sharply from the forty-eight inherited from antiquity.