The Constellation Eridanus
Last week, we looked at the grand constellation Orion. Today, for Beginner’s Corner, let’s stay in the same part of the sky to find the long constellation Eridanus (“air-RID-in-us”), the River, which winds from the foot of Orion into the deep southern sky. The constellation contains the bright star Achernar, as well as a fainter star that’s home to a famous (and fictional) alien with a logical mind and pointed ears…
This constellation has a rich history, and takes its name from the ancient Greek name for the Po River in northern Italy. Eridanus dates back to the 2nd century A.D., when the astronomer Ptolemy included it in his original list of 48 constellations.
Eridanus begins near the star Cursa, just west of Rigel, in Orion, and moves straight west, cuts back east, then drops directly south. Only stargazers in the southern hemisphere can see all of it, including the bright star Achernar at the end of this celestial river. The constellation lies nearly overhead for observers in the southern hemisphere this time of year.
Here’s a map to show you the full length of the constellation, as seen from about 35 degrees south latitude.
——————– From Stargazer University ——————–
Around the Moon in 28 Days takes you on a full tour of the Moon during the month. Learn the seas, highlands, craters and mountains of the Moon, and get a glimpse of the solar system in its earliest days. Click here to learn more…
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A wide-view map showing the long and winding constellation Eridanus (click to enlarge).
Achernar (“AK-er-nar”) is the ninth brightest star in the sky. It shines some 3000 times brighter than the sun. It’s an odd star. It spins so rapidly, its equatorial length is 50% larger than its polar length, and likely appears like a squashed ball (see the image at the top of the page). Achernar is the only bright star in this part of the sky, so it’s hard to miss.
And have a look at the close pairing of stars just south and west of Rigel. Astronomers cataloged these two stars as “omicron 1″ and “omicron 2″. Omicron 2, which is the fainter of the two, is also called 40 Eridani. It’s a binary star, just 16 light years away. The main component, called 40 Eridani A, is a red dwarf, just slightly smaller than our Sun. Its companion star, 40 Eridani B, which can be seen with a telescope, is a white dwarf. As massive as the Sun but not much larger than the Earth, a white dwarf is the hot dense leftover core of a star that’s run out of fuel. Most small and mid-sized stars, the Sun included, will end their lives as a white dwarf.
And though it can’t be detected directly, the white dwarf 40 Eridani B has itself a small red-dwarf companion called 40 Eridani C.
And if you’re a big Star Trek fan… you may know know that 40 Eridani A is the fictional home star of the planet Vulcan and Mr. Spock. No sign yet of any life in this star system, however.
