Eridanus constellation
Eridanus (the River) is a constellation in the southern sky, best seen in the evening in December. Its brightest star is Achernar (magnitude 0.46). Eridanus covers 1,138 square degrees and is the 6th-largest of the 88 constellations.
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Detailed star map of Eridanus
Facts
| Latin name | Eridanus (genitive: Eridani) |
|---|---|
| Abbreviation | Eri |
| Meaning | the River |
| Area | 1,138 square degrees (6th of 88) |
| Location | right ascension 3.6 h, declination −29° |
| Visible from | latitudes 32° N to 90° S (whole constellation) |
| Best month | December (at about 9 pm) |
| Brightest star | Achernar |
| Stars brighter than magnitude 6 | 131 |
| Named stars (IAU) | 14 |
| Messier objects | none |
| Neighbors | Caelum, Cetus, Fornax, Horologium, Hydrus, Lepus, Orion, Phoenix, Taurus |
How to find Eridanus
From 40° N (the USA, southern Europe, Japan) look south in December evenings: at about 9 pm Eridanus stands highest, around 21° above the southern horizon. From 35° S (Australia, South Africa, Argentina) it is highest in the north, about 84° above the horizon. The months before and after (November and January) are also good: then it is up a couple of hours earlier or later.
Eridanus borders Caelum, Cetus, Fornax, Horologium, Hydrus, Lepus, Orion, Phoenix and Taurus.
Stars of Eridanus
Eridanus has 131 stars brighter than magnitude 6, the limit of the naked eye under a dark sky. These are the brightest:
| Star | Designation | Magnitude | Type | Distance |
|---|---|---|---|---|
| Achernar | α Eridani | 0.46 | B3Vpe | 144 ly |
| Cursa | β Eridani | 2.79 | A3III | 90 ly |
| Zaurak | γ Eridani | 2.95 | M0.5IIICa-1Cr-1 | 192 ly |
| Acamar | θ1 Eridani | 3.24 | A4III | — |
| Rana | δ Eridani | 3.54 | K0+IV | 30 ly |
| — | φ Eridani | 3.56 | B8V-IV | — |
| — | υ4 Eridani | 3.56 | B9V | — |
| — | τ4 Eridani | 3.69 | M3.5IIIaCa-1 | — |
| — | χ Eridani | 3.7 | G8IIIbCNIV | — |
| Ran | ε Eridani | 3.73 | K2V | 11 ly |
| Theemin | υ2 Eridani | 3.82 | G8IIIa | 211 ly |
| Sceptrum | 53 Eridani | 3.87 | K2IIIb | 116 ly |
Printable Eridanus map and outline
A black and white version for printing and a plain outline of the Eridanus figure, useful for school projects, worksheets and learning to recognize the shape.
History
Eridanus is one of the 48 constellations listed by Ptolemy in the Almagest (2nd century AD). Its official boundary was drawn by Eugène Delporte for the International Astronomical Union in 1930.
Questions about Eridanus
What is the brightest star in Eridanus?
Achernar, at magnitude 0.46, about 144 light-years away.
When can you see Eridanus?
Eridanus is best seen in the evening in December. The whole constellation is visible from latitudes between 32° N and 90° S.
How many stars are in Eridanus?
131 stars in Eridanus are brighter than magnitude 6 and can be seen with the naked eye under a dark sky; 14 of them have official IAU names.
What does Eridanus mean?
Eridanus means “the River” in Latin. Its abbreviation is Eri and the genitive, used in star names such as α Eridani, is Eridani.
