Gaze skyward on cold winter evenings and you’ll find it hard to ignore Orion the hunter, standing stoically in the south. Even those of us who just accidentally glance upward as we race from our cars to our nice warm homes almost instantly notice the four bright stars that outline a rectangle and the three more that trace a straight line in its center.
While Orion unquestionably represents the season’s most attention-grabbing star grouping, it’s not the only constellation in that area of the sky. In fact, one of the longest of all constellations begins near the foot of the great hunter. Its name is Eridanus, the river.
In Greek mythology, Eridanus is the river in which young Phaethon crashed after his failed attempt to fly the chariot of the sun. But no one knows exactly which river Eridanus was supposed to represent. Some claim it’s the Tigris or the Euphrates; others suggest it is the river Po, or possibly even the mighty Nile.
Finding this sinuous string of relatively faint stars isn’t all that difficult. First locate the southwesternmost star of Orion, Rigel. Next, look just above and to its right for the fainter star that marks the head of the celestial river. If you’ve got a dark night and a fairly low southern horizon, you should be able to trace the river as it meanders south and to the west.
Northern Hemisphere stargazers can see only a portion of it. In fact, if you live in middle or high latitudes, you might only be able to trace one-third or half of the river. Those living in more southerly locations will see more. Only those who do their stargazing near or south of the equator can see the entire constellation, as it meanders almost all the way toward the south celestial pole.
Though the constellation is rather obscure, one of its stars has captured the imagination of astronomers and science fiction authors alike. Its name is Epsilon Eridani, a slightly orange star appearing about midway down the constellation’s winding stellar string. You might recognize its name from science fiction novels by Isaac Asimov and Frank Herbert, as well as from the popular TV series Babylon 5.
It was back in 1960 when scientists proposed that because the star lies relatively nearby — only about 10.5 light-years from Earth — aiming a radio telescope in its direction might detect signals from an intelligent civilization orbiting on possible nearby planets. And that’s exactly what astronomers did; unfortunately, they have yet to receive signals from such a civilization.
They have not stopped their monitoring programs, however, for today we know much more about Epsilon Eridani, and astronomers are even more intrigued. The star appears to be a much younger version of our own sun, circled by a disk of dusty debris.
In addition, astronomers have confirmed that orbiting nearby, there is a Jupiter-like planet they have named Aegir, and possibly a much smaller body still officially designated as Epsilon Eridani c.
Might this nearby star be a mighty sun of worlds harboring life? We don’t yet know, but it’s always fun to gaze upon its light and wonder.
— Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at mammana@skyscapes.com and follow him on Twitter: @dennismammana. The opinions expressed are his own.