Located in the southern celestial hemisphere, the constellation Eridanus is represented as a river. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and is the 6th largest modern constellations. The constellation’s name was was later used as a Latin name for the river Po in Italy. In Sanskrit, Eridanus is called srotaswini, which means “stream,” “current,” or “torrent.”

Achernar, the constellation’s brightest star, is the ninth brightest star in the sky.

Eridanus has many deep sky objects, including the CMB Cold Spot, the Eridanus Group of galaxies, and the Witch Head Nebula.

Applicable Information
Visibility In Pacific NorthwestSeptember to March
Best Times To ViewDecember
Right Ascension3.25h
Area1138 square degree
Main Stars24
Brightest ObjectAchernar (α Eri) 
Meteor showers0
Messier objects0
Neighboring ConstellationsCetus, Fornax, Phoenix, Hydrus, Horologium, Caelum, Lepus, Orion, Taurus, Tucana

History / In Culture

Some have said that the name Eridanus in the Greek constellation takes its name from the Babylonian constellation known as the Star of Eridu.

Eridanus is also associated with some rivers across the world, such as the Nile River in Egypt and the Po River in Italy.

Indian astronomers also depicted Eridanus as a river. Eridanus is associated with the river Ganges.


At its southern end of the constellation is located the star Achernar, or Alpha Eridani. It is one of the flattest known star, as the radius is larger at the equator than is the poles, per observations. However, this is caused by distortions due to the rotation of the star.

There is an area of the universe that is devoid of galaxies in the constellation called, “the Eridanus Supervoid.” 

There is a planetary nebula called NGC 1535, which is visible in small amateur telescopes.

Illuminated by a nearby supergiant star, the reflection galaxy IC 2118 is very faint and is believed to be an ancient supernova remnant or gas cloud.

The galaxies NGC 1232, NGC 1234, NGC 1291 and NGC 1300 can all be found in the constellation.

Make sure to check out other articles on the site, including a brief introduction to constellations, other constellation articles, and more!

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