Eridanus was the ancient Greek name for today’s Po River. This constellation was one of the 48 constellations cataloged by the 2nd century astronomer Ptolemy that remain among the 88 modern constellations. This southern constellation has the distinction of being sixth largest of the modern constellations, and is best seen at its highest nightfall ascension in January. The river begins near Orion’s left foot and flows southward from there. At our 40-degree north location, the southern, or lower half of the constellation remains hidden below the horizon. At the southern end of Eridanus is the magnitude 0.5 star Achernar whose traditional name means “the river’s end.”
Of particular interest in this constellation is the Eridanus Supervoid. Numerous galaxies can be seen in deep exposure photographs in almost every direction when looking outward into the Universe beyond the foreground Milky Way stars, but the sky in the direction of Eridanus is almost entirely void of distant galaxies.
© James R. Johnson, 2014.