Eridanus's boundaries enclose a larger area of sky that any other constellation, but most of its stars are 3rd magnitude and fainter. There are exceptions, however.
Achernar(also known as Alpha Eridani) is the 9th brightest star in the sky, even though it is a distant 70 light years away. It is blue/white in color, and has a magnitude of 0.46. Its name, Achernar, means "mouth of the river" in Arabic, which is fitting, as it is the southernmost point in Eridanus. In fact, Achernar is so far south that it cannot be seen from points north of southern Florida and Texas.
At the northernmost end of Eridanus, is Cursa, or Beta Eridani. Cursa means "the chair or footstool of Orion", Orion being the constellation directly above Eridanus. Cursa, with a fainter magnitude of 2.79 (bigger magnitudes means dimmer stars) is 78 light years away. Technically, it is a white star, but visually, it appears a topaz yellow. This may be due to its contrast with the nearby blue/white star Rigel, or it could be due to atmospheric conditions. Either way, even the Chinese noted its yellowish color, by calling the star "Yuh Tsing", which means "Golden Well".
Towards the western edge of Eridanus, is Gamma Eridani, also known as Zaurak. Zaurak's name appropriately means "boat". It is a reddish star, magnitude of 2.95, with a small companion star.
Northwest of Zaurak is Epsilon Eridani, which is of interest to us because it is so nearby. At only 10.8 light years away, it has a low-mass, unseen companion.
In ancient days, Cursa, in combination with Omicron 1 and 2 Eridani, were called the "Ostrich's Nest". Omicron 1 was called Al Baid or "The Egg", and Omicron 2 was Al Keid, or "The Eggshells". Omicron 2, also known as 40 Eridani, is actually a system of 3 stars, named A, B, and C, all located about 16 light years away. 40 Eridani A is an orange main-sequence star like the sun, only slightly cooler. In 1783, Sir William Hershel discovered that it had a companion. The two are separated by 400 astronomical units (that is 400 times the distance between the earth and the sun), and only complete a full orbit around their common center of mass once every several thousand years!
In 1851, Otto Struve discovered that this companion was actually two stars, a white dwarf (40 Eridani B) and a small red dwarf star with a mass of only 0.2 times the sun's mass (40 Eridani C). These two stars are only separated by 34 astronomical units, and complete an orbit every 248 years. 40 Eridani B, the 9th magnitude white dwarf, is the easiest white dwarf to observe with a small telescope. This system of stars was also used to verify Einstein's theory of relativity, by showing that the white dwarf's spectral lines are redshifted by gravity.
There are other items of interest in this constellation, such as the galaxy NGC 1637, located slightly northwest of Mu Eridani, and the planetary nebula NGC 1535, southwest of Gamma Eridani. The Orion Eridanus Superbubble is also located in this area of the sky. For more information on what superbubbles are, please visit the Penn State X-ray Group's Superbubbles page.
For more information on Eridanus and its named stars, see Chris Dolan's Eridanus page.
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Mythology