What it looks like
Eridanus is a vast, meandering constellation representing a celestial river. It begins near the foot of Orion, flows westward, then plunges south through the sky, ending at the bright blue star Achernar near the southern celestial pole. Because of its great length, only the northern half is visible from mid-northern latitudes.
Brightest stars
Eridanus is anchored by Achernar, a brilliant blue star and the ninth-brightest in the night sky, plus Cursa at the river's source.
| Star | Magnitude | Distance | Meaning |
|---|---|---|---|
| Achernar (α Eridani) | +0.46 | 139 ly | End of the River |
| Cursa (β Eridani) | +2.79 | 89 ly | The Footstool |
| Acamar (θ Eridani) | +2.88 | 161 ly | End of the River |
| Zaurak (γ Eridani) | +2.95 | 203 ly | — |
| Rana (δ Eridani) | +3.54 | 29 ly | The Frog |
Mythology and history
In Greek myth, Eridanus is the river into which Phaethon fell after losing control of the Sun's chariot, and where the Heliades sisters wept amber tears for him.
Phaethon's fall
Phaethon, son of Helios the Sun, begged to drive his father's chariot across the sky for a day. Unable to control the horses, he scorched the earth and was struck down by Zeus's thunderbolt, falling into the river Eridanus. His sisters, the Heliades, mourned so long on the riverbank that the gods turned them into poplar trees, and their tears became amber. The river is sometimes identified with the Po in Italy or the Rhine in Germany, but the constellation simply represents a great celestial river.
How to find it
Start at Cursa just below Rigel in Orion, then follow the long chain of faint stars westward and southward.
- Find Cursa first, then follow the chain west and south.
- Achernar, at the southern end, is not visible from mid-northern latitudes.
- Best on winter evenings; fully visible only from the southern hemisphere.
Key facts
- Abbreviation
- Eri
- Genitive
- Eridani
- Meaning
- The River
- Brightest star
- Achernar
- Main stars
- 18
- Area rank
- 6th
- Best visible
- December
- Declination
- -30°
- Meteor showers
- —
- Neighbours
- Cetus, Fornax, Phoenix, Hydrus, Tucana, Horologium, Caelum, Lepus, Orion, Taurus
Deep-sky objects
Eridanus contains the Witch Head Nebula (IC 2118), a reflection nebula near Rigel, and NGC 1300, a classic barred spiral galaxy. The constellation also contains the Eridanus Cluster of galaxies and the Eridanus Supervoid, a vast region of space that is unusually empty.
Frequently asked questions
What does the constellation Eridanus look like?
Eridanus is the sixth-largest constellation, known as the River, a long winding chain of stars that starts near Orion and ends at brilliant blue Achernar in the far south.
What is the brightest star in Eridanus?
The brightest star in Eridanus is Achernar, shining at around magnitude 0.46.
When is Eridanus best visible?
Eridanus is best seen from both hemispheres during December.
What is the story behind Eridanus?
In Greek myth, Eridanus is the river into which Phaethon fell after losing control of the Sun's chariot, and where the Heliades sisters wept amber tears for him.
Which constellations are near Eridanus?
Eridanus borders Cetus, Fornax, Phoenix, Hydrus, Tucana, Horologium, Caelum, Lepus, Orion and Taurus.
Orion
Cetus