Eridanus is the 6th largest constellation in the sky. It is part
of the constellation family The Heavenly Waterrs, located
in the north, Cetus to the
northwest, Fornax and
Phoenix to the southwest,
Hydrus to the south and
Orion to the east.
It streches from the celestial equator to the far south, roughly from RA = 0 degrees to RA = - 58 degrees and Decl = 1h 20m to Decl = 5h 10m.
The river Eridanus is thought to originate near the star Rigel (belongs to the constellation Orion) and ends at its brightest star alpha Eri.
Despite of its size there are not many bright stars in this constellation. Notable are alpha Eri, called Achernar (arab.: end of the river), with 0.5 mag the 6th brightest star in the sky, and epsilon Eri, a star similar to our sun, which is just 10.7 light years away.
There are several faint galaxies within this constellation, but there are too faint to be observable by amateur scopes. Yet they show up nicely on long-exposure photographs.
Stars and other objects
In small telescopes theta Eri reveals a magnificent pair of
bluewhite stars of 3rd and 4th magnitude.
In a distance of about 220 light years the double 32 Eri is located. It consists of a 5th mag and a 6th mag star in the colors yellow and blue-green. Small scopes resolve this pretty pair.
The double f Eri is a wide pair consisting of a 4.9 mag and a 5.4 mag component.
The binary p Eri lies just north of alpha Eri. Its a wide pair of orange stars of 6th mag.
Omicron2 Eri (also called 40 Eri) is a striking triple star system. One of the stars is the most easily observable white dwarf to amateur telescopes. The main star of the triplet is a yellow dwarf of 4th mag. With a small scope one immediately discovers the 10th mag companion, which is the white dwarf mentioned above. With larger scopes (10cm aperture or more) can resolve the third member of the system, a red dwarf of 11 mag.
The planetary nebula NGC 1535 shows up in small scopes as a blue-white colored disk. The nebula actually consists of two rings, a bright inner ring and a faint outer ring. The brightness of this nebula is of 9th magnitude.
I 2118 is the so called Witch Head Nebula. It is located about 1.5 degrees south of beta Eri and 2 degrees northwest of beta Ori.
According to Greek mythology Eridanus represents the river into which Pheaton fell from the chariot he borrowed from the Sun God.