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See a winding river of stars called Eridanus


Tonight for January 11, 2015

Here’s a constellation for you if you have access to a very dark sky: Eridanus the River. You won’t see this one from the city, or even the suburbs. Eridanus the River begins near the star Rigel in the constellation Orion the Hunter – and wells up in a great loop before ambling back down toward the southern horizon.

Before nightfall, however, look for the close pairing of the planets Venus and Mercury in the western dusk. You can’t miss Venus, the third-brightest celestial object in all the heavens, after the sun and moon. If you can’t see Mercury with the unaided eye, try your luck with binoculars. Mars will stay out after dark. Click here for a sky almanac.


Back to Eridanus, one of the longest and faintest constellations. It’s variously said to represent the Nile in Egypt, Euphrates in western Asia, or the River Po in Italy. Eridanus is also sometimes called the River of Orion, or River of Ocean. In Homer’s day in ancient Greece, it was thought that the River of Ocean encircled a flat Earth.

Why search for such a faint constellation? Only because it’s very beautiful. And seeing Eridanus – understanding its association with a river in the minds of the early stargazers – can give you a kinship with those stargazers from centuries ago.

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The constellation Eridanus the River. Click here for a larger chart

From most of the U.S., the River disappears below the southern horizon. But if you live at a very southerly latitude in the U.S., you can see a special sight: the star that represents the end of the River. This star is named Achernar.

Here’s the real River Po as captured at sunset by EarthSky Facebook friend Marco Mereu, in February 2013. Thank you Marco! View larger.

Bottom line: Can you find the long, meandering river of stars called Eridanus in your sky? Be sure to look from a dark location.

Star Achernar marks the end of the River

January 2015 guide to the five visible planets