Eridanus (ĭrĭdˈənəs) [key], large southern constellation stretching SW from Orion for about 60°. Because of its long, winding shape it was identified with a river by many ancient civilizations; e.g., the Egyptians called it the Nile and the Babylonians called it the Euphrates. The brightest star in the constellation, Achernar, marks the southern end of the river. Eridanus reaches its highest point in the evening sky in December.
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