The River Eridanus is a long and winding constellation with one of the brightest stars in the sky, seen only by southern observers.
In the sky, Eridanus is a river of stars and was considered representative of long rivers on Earth. In times past, the people of Egypt saw Eridanus as the Nile, Italians saw it as the Po, and Chinese saw it as the Yellow River. Read more about the mythology of Eridanus.
Location
Eridanus can be found next to Orion. The bottom right "foot" or "knee" star in Orion, Rigel, is right next to Eridanus, which then stretches west, south, and zig zags southwest into Southern Hemisphere skies.
Stars
Eridanus's brightest star, Achernar, lies at the far southern border of the constellation and is not visible to most northern observers. People living in Southern Florida can spy Achernar rise just above the southern horizon on fall evenings. Achernar is a magnitude 0.45 beacon that lies 144 light-years away. It is the ninth brightest star in the sky.
The second brightest star in Eridanus lies back in the north next to Rigel in Orion. Three and a half degreesw to Rigel's upper right is the magnitude 2.78 star Cursa, which lies 89 light-years away. Just below it is the Witch Head Nebula. See Deep-Sky Objects below for more information.
Heading west and slightly south of Cursa, near the middle of Eridanus's wider upper constellation borders, is the magnitude 2.97 Zaurak. It lies 221 light-years away. Farther west and nearing the body of Cetus the Whale is magnitude 3.89 Azha. Almost 31 and a half degrees directly south of Azha is another named star of Eridanus: Acamar. If you followed the line south from Azha to get to it you crossed in and out of the constellation Fornax, which Eridanus winds around. Acamar is a magnitude 2.88 star lying 161 light-years away.
Deep-Sky Objects
The most notable deep-sky object in all of long and winding Eridanus lies back up next to Orion. Just across the border from Orion near the star Rigel is the famous Witch Head Nebula, or IC 2118. The nebula looks a bit like an old hag's face shown in profile. The nebula is very long in extent but also faint and difficult for beginning observers to see. For more on the Witch Head Nebula, see Halloween Stargazing.
A planetary nebula lies on a line four-fifths of the way from Rigel to Zaurak. The nebula is NGC 1535. This planetary nebula is magnitude 10 can be picked up with smaller telescopes but really excels with a larger aperture.
