Eridanus (Pronounciation:Iri-dan-us, Abbrev:Eri, Latin:Eridani) is a constellation, one of 88 constellations that the night sky is divided into. The sky is not divided up equally between the constellations. Eridanus takes up 1137.919 sq. degrees of the night sky which equates to 2.76% of the night sky. Eridanus is the 6th largest in terms of size in the night sky.
The constellation name means River Eridanus . The constellation is one of the original constellations that was devised by the Ancient Greco-Egyptian astronomer Ptolemy who lived between 90 A.D. and 168 A.D.
There are 31 stars that make up the main constellation. The hipparcos satellite scanned and detailed 2759 stars. There are 128 stars that can be seen with the naked eye in the constellation on a very clear night sky.
Eridanus is not a member of the Zodiac group of twelve constellations that appear when the Sun sets. Eridanus is a southern hemispheric constellation which means it can't be seen easily or at all from the northern hemisphere.
There are 32 Extrasolar Planets (Exoplanets) in this constellation that are detailed on this site. There is a dedicated page for exoplanets in Eridanus.
There are no deep space objects that were identified by Charles Messier in this constellation. There are 2 non-Messier deep space objects that are covered on this site and the list is below.
The image at the top right of this page was generated using Night Vision, a free to use and download application by Brian Simspon.
You can't just go to one location and arrive at the constellation because the constellation is made up of stars at different locations and different distances. The nearest main star in the constellation is at a distance of 10.49 light years and the furthest main star is a distance of 1,475.85 light years. The average distance to the main stars is 254.13 light years.
The caveat of these stars are that they are catalogued on this site. If you know of a star that is nearer or further then do let me know in the comments and I'll add it to the site. The stars mentioned are from the Hipparcos catalogue or have been added because of their special status.
The furthest star that is located in the constellation is HIP 13391 and it is 326163.3 light years away from the Sun. The furthest figure is derived from either the 1997 or 2007 Hipparcos star catalogue parallax figure and it has been known to produce distances that are wrong.
The dimmest star that can be seen in Eridanus with the naked eye is GZ Eridani. The dim star has an apparent magnitude of 6. The dimmest star that a person is able to see with their naked eye is 6.0 magnitude based on the table in the reference. Ref: University of Michigan.
Achernar is at the southern end of the river and is as far as you can get from the the second brightest, Cursa which is also known as Beta Eridani. The most interesting thing about the star is its shape. Achernar is not spherical like most star, its has flattened out, caused by its rotation and its pull by other stars.
At the very top of the star is Cursa, the second brightest star in the constellation. Its as far as you can get from the brightest star in a single constellation. It is in the Northern hemisphere whereas Achernar is in the southern.
40 Eridani or Keid which is easier to remember is best remembered amongst trekkies for being the home star for Vulcan. The star was chosen by Gene Roddenberry. The star is a multi-star system and any planet would have a two star sky line much like Tatooine in Star Wars, the "rival" space franchise. At present, no planets have been spotted orbiting the star.
18 Eridani is one of the closest stars to Earth that has exoplanets orbiting it. For a long time, 18 Eridani was also referred to as Sadira but when the IAU ran a competition, they ignored the name and chose Ran instead for its name.
Eridanus, the river was where Phaethon fell into when he was knocked out of his chariot basket. Phaethon had taken his father Helios' chariot and rode it across the skies both too high and too lower. As it was scaring the people below, Zeus threw fire bolts at the chariot to stop him. The chariot stopped but Phaethon fell out and into the river.
Eridanus is never fully visible in the Northern hemisphere, in London at least. You will never see the southern tip of it, that is Achernar. You are able to see the Witch-Head Nebula, a reflection nebula that is lit up by radiation from Rigel in neighbouring Orion constellation. The most southern star would be G Eridani, anything more south, you will not be able to see in London. If you head south, you'll have better luck at seeing the southern stars including the Alpha Star.
The Southern Hemisphere has a good view of the constellation and is fully visible from November to April time. Eridanus lays across the sky. It fully disappears from May until September when it slowly begins to appear on the horizon led by its Alpha star, Achernar.
There are 14 Meteor Showers that occur during the year within this constellation based on information gathered from Adam Mickiewicz University (Poland). The list below are major ones and which I have a date period for.
| Name | Activity | Peak Activity | Closest Star |
| Nu Eridanids | 24th Sept | ||
| upsilon Eridanids | 16th January | ||
| Eta Eridanids | 3 Aug- 14 Aug | 09-Aug | Azha |
| November epsilon Eridanids | 23rd November |
The following list contains the stars that make up the constellation. For a larger list of stars in the entire constellation area, please visit the For a list of named stars, that is stars that don't start HD or HIP, please visit Eridanus Star List page.
| Name | Bayer | Distance (Lt.Yr.) | Right Ascension | Declination | Spectral Type | Colour |
| Achernar | Alpha Eridani | 139.45 | 01h 37m 42.75 | -57d 14` 12.0 | B3Vp | Blue/White |
| Cursa | Beta Eridani | 89.36 | 05h 07m 51.03 | -05d 05` 10.5 | A3IIIvar | White |
| Zaurak | Gamma Eridani | 203.34 | 03h 58m 01.73 | -13d 30` 29.7 | M1IIIb Ca-1 | Red |
| Rana | Delta Eridani | 29.49 | 03h 43m 14.96 | -09d 45` 54.7 | K0IV | Orange |
| Ran | Epsilon Eridani | 10.49 | 03h 32m 56.42 | -09d 27` 29.9 | K2V | Orange |
| Zibal | Zeta Eridani | 109.75 | 03h 15m 50.03 | -08d 49` 11.4 | A5m | White |
| Azha | Eta Eridani | 136.53 | 02h 56m 25.60 | -08d 53` 51.4 | K1III-IV | Orange |
| Iota Eridani | Iota Eridani | 150.65 | 02h 40m 39.93 | -39d 51` 19.1 | K0III | Orange |
| Kappa Eridani | Kappa Eridani | 508.04 | 02h 26m 59.10 | -47d 42` 13.8 | B5IV | Blue/White |
| Mu Eridani | Mu Eridani | 521.86 | 04h 45m 30.14 | -03d 15` 16.6 | B5IV | Blue/White |
| Nu Eridani | Nu Eridani | 675.29 | 04h 36m 19.14 | -03d 21` 08.8 | B2III SB | Blue/White |
| Beid | Omicron1 Eridani | 121.70 | 04h 11m 51.93 | -06d 50` 16.0 | F2II-III | Yellow/White |
| Pi Eridani | Pi Eridani | 481.07 | 03h 46m 08.50 | -12d 06` 06.2 | M1III | Red |
| Tau6 Eridani | Tau6 Eridani | 57.49 | 03h 46m 50.99 | -23d 14` 54.4 | F3/F5V | Yellow/White |
| Tau7 Eridani | Tau7 Eridani | 250.89 | 03h 47m 39.62 | -23d 52` 29.3 | A1V | White |
| Tau8 Eridani | Tau8 Eridani | 377.07 | 03h 53m 42.68 | -24d 36` 44.0 | B5V | Blue/White |
| Tau9 Eridani | Tau9 Eridani | 327.47 | 03h 59m 55.48 | -24d 00` 58.5 | Ap Si | White |
| Tau4 Eridani | Tau4 Eridani | 304.54 | 03h 19m 30.97 | -21d 45` 28.6 | M3/M4III | Red |
| Tau1 Eridani | Tau1 Eridani | 46.38 | 02h 45m 05.98 | -18d 34` 21.5 | F5/F6V | Yellow/White |
| Tau3 Eridani | Tau3 Eridani | 88.63 | 03h 02m 23.59 | -23d 37` 27.6 | A4V | White |
| Upsilon1 Eridani | Upsilon1 Eridani | 127.06 | 04h 33m 30.63 | -29d 45` 57.0 | K0III | Orange |
| Upsilon4 Eridani | Upsilon4 Eridani | 177.94 | 04h 17m 53.62 | -33d 47` 54.0 | B9V | Blue/White |
| Beemin | Upsilon3 Eridani | 296.24 | 04h 24m 02.17 | -34d 01` 01.2 | K4III | Orange |
| Phi Eridani | Phi Eridani | 153.71 | 02h 16m 30.50 | -51d 30` 43.6 | B8IV-V | Blue/White |
| Chi Eridani | Chi Eridani | 58.22 | 01h 55m 56.83 | -51d 36` 34.5 | G5IV | Yellow |
| S Eridani | 290.18 | 04h 59m 55.71 | -12d 32` 13.9 | F0V | Yellow/White | |
| G Eridani | 209.89 | 03h 49m 27.28 | -36d 12` 00.4 | G8III | Yellow | |
| H Eridani | 184.27 | 03h 42m 50.12 | -37d 18` 48.0 | K2IIICN... | Orange | |
| 15 Eridani | 255.41 | 03h 18m 22.10 | -22d 30` 40.1 | K0III | Orange | |
| Y Eridani | 1475.85 | 02h 05m 34.16 | -57d 08` 39.0 | Me | Red | |
| 82 Eridani | 19.71 | 03h 19m 53.22 | -43d 04` 17.6 | G8V | Yellow |
| Name | Eridanus |
| Abbreviation | Eri |
| Is a Zodiac Sign | No |
| Brightest Star | Achernar |
| Area | 1137.919 sq. deg. |
| Percentage of Night Sky | 2.76% |
| Size Position | 6th |
| Hemisphere | Southern |
| Site Exoplanet Count | 32 |
| Meteor Shower Count | 14 |
| Nearest Star | Ran |
| Nearest Star with Exoplanet(s) | Sadira |
| Brightest Star | Achernar |
| Dimmest Star | GZ Eridani |
| Furthest Star | HIP 13391 |
| Bright Star Count | 128 |
| Hipparcos Star Count | 2759 |
| Main Star Count | 31 |
| Messier Deep Space Object Count | 0 |
| Bordering / Neighbouring / Surrounding Constellations | Taurus |
| Cetus | |
| Fornax | |
| Phoenix | |
| Tucana | |
| Horologium | |
| Caelum | |
| Lepus | |
| Orion |
*Note: The number of Non-Messier Deep Space Object Count relates to how many are covered on this site not how many there are.
| Name | Type | Distance | Declination | Right Ascension |
|---|---|---|---|---|
| NGC 1234 | Lenticular Galaxy | -07 50 43.39 | 03 09 39m 000 | |
| NGC 1300 | Barred Spiral Galaxy | 61,000,000 | -19:24.41 | 03h 19h 41m 1 |
| NGC 1309 | Spiral Galaxy | 100,000,000 | -15 23 47.70 | 3 22 5m 69 |
| NGC 1332 | Galaxy in a Pair of Galaxies | -21 20 07.33 | 03 26 17m 321 | |
| NGC 1427A | Irregular Galaxy | 50,000,000 | -35:37:17.74 | 3 40 9m 41 |
| NGC 1627 | Galaxy | -04:53:80527 | 04h 37h 38m 01515 | |
| NGC1600 | Galaxy | 200,000,000 | -05 05 09.97 | 04 31 39m 858 |
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