Constellation Eridanus (River)

Eridanus: IAU Constellation Map [150]


The elongated constellation is the sixth largest figure in the sky with an area of 1138 square degrees, but due to the mostly faint stars it is hardly noticeable. The river meanders from Rigel in Orion to Cetus in the west and then down south to Hydrus, where it ends with the brightest star in this constellation, Achernar. Achernar culminates around midnight on October 14th and the center of the constellation around November 10th. [9, 15]

Stars with Proper Names [154]
α Eri Achernar
β Eri Cursa, Dhalim, Kursa
γ Eri Zaurak, Zaurac, Zaurack
δ Eri Rana
ζ Eri Zibal
η Eri Azha
θ1 Eri Acamar
ο1 Eri Beid
ο2 Eri Keid, Kied
τ2 Eri Angetenar, Al Anchat Al Nahr, Anchat
υ2 Eri Theemim, Beemin
53 Eri Sceptrum
Data for constellation Eridanus [150]
IAU NameEridanus
IAU GenitiveEridani
IAU Abbr.Eri
English NameRiver
Opposition23 November
Season (47° N)September … February
Right Ascension01h 24m 49s … 05h 11m 13s
Declination-57° 54' 58" … +00° 24' 13"
Area1138 deg2
Neighbours (N↻)Tau, Cet, For, Phe, Tuc, Hyi, Hor, Cae, Lep, Ori

Deep-Sky Object Descriptions


Constellation Eridanus
Constellation Eridanus: Illustration from «Uranometria» by Johann Bayer, copper engraving by Alexander Mair, 1603 [28]

Mythology and History

In Greek mythology, Eridanus is the river into which Phaethon, the lover of Cyknos, fell when he tried to drive his father Helios' sun chariot across the sky. But there have also been attempts to connect it to an earthly river, the Po in northern Italy, the Nile or the Euphrates.

Originally Eridanus ended at the star θ Eridani, whose name Acamar is derived from Achernar (end of the river); at that time the stars of Fornax still belonged to Eridanus. Eridanus was later extended to almost 60 degrees south latitude. Another star was given the nickname Achernar. [7]


  • [7] «Der grosse Kosmos-Himmelsführer» von Ian Ridpath und Wil Tirion; Kosmos Verlag; ISBN 3-440-05787-9
  • [9] «Drehbare Sternkarte SIRIUS» von H. Suter-Haug; Hallwag-Verlag, Bern
  • [15] «Hartung's Astronomical Objects for Southern Telescopes» by David Malin and David J. Frew; Melbourne University Press 1995; ISBN 0-522-84553-3
  • [28] «Uranometria omnium asterismorum continens schemata, nova methodo delineata aereis laminis expressa» Johann Bayer, Augsburg, 1603; DOI:10.3931/e-rara-309
  • [150] IAU: The Constellations, 11. Oktober 2020;
  • [154] Yale Bright Star Catalog, 15. Oktober 2020;