Constellation, Eri
Eridanus: the River
Eridanus covers 1,138 square degrees of sky, the 6th largest of the 88. Its brightest star is Achernar. It is best placed in the evening sky in January.
Eridanus at a glance
| Fact | Value |
|---|---|
| IAU abbreviation | Eri |
| Meaning | the River |
| Pronounced | ih-RID-un-us |
| Genitive, used in star names | Eridani (for example a Bayer name such as α Eridani) |
| Area | 1,138 square degrees, number 6 of 88 by size |
| Stars to magnitude 6 in our catalogue | 128 |
| Brightest star | Achernar, magnitude 0.5 |
| Best seen | Evenings in January, when it is highest at 9 pm |
| Declination range | -58° to 0° |
| Borders | Fornax, Horologium, Phoenix, Cetus, Taurus, Lepus, Caelum, Orion, Hydrus, Tucana |
Where on Earth you can see Eridanus
Eridanus spans declinations -58° to 0°. Every part of it rises above the horizon at some moment for observers between latitudes 90°S and 32°N. Some of it can be seen from every latitude. This is geometry only: it ignores haze, hills and buildings near the horizon.
From six cities
| City | Latitude | Visibility | Middle at its highest |
|---|---|---|---|
| Pune | 18.5°N | All of it rises | 50° |
| New York | 40.7°N | Only part of it rises | 27° |
| London | 51.5°N | Only part of it rises | 17° |
| Tromsø | 69.6°N | Only part of it rises | below the horizon |
| Tokyo | 35.7°N | Only part of it rises | 32° |
| Sydney | 33.9°S | All of it rises | 78° |
Eridanus's named stars
These stars in Eridanus have names approved by the IAU Working Group on Star Names. Magnitude is brightness: a lower number is brighter, and the faintest stars seen with the naked eye on a dark night are about magnitude 6.
| Star | Designation | Magnitude | Distance (light-years) |
|---|---|---|---|
| Achernar | α Eridani | 0.45 | 140 |
| Cursa | β Eridani | 2.78 | 89.4 |
| Acamar | θ1 Eridani | 2.88 | 160 |
| Zaurak | γ Eridani | 2.97 | 200 |
| Rana | δ Eridani | 3.52 | 29.5 |
| Ran | ε Eridani | 3.72 | 10.5 |
| Theemin | υ2 Eridani | 3.81 | 210 |
| Sceptrum | 53 Eridani | 3.86 | 110 |
| Azha | η Eridani | 3.89 | 140 |
| Beemim | υ3 Eridani | 3.97 | 300 |
| Beid | ο1 Eridani | 4.04 | 120 |
| Keid | ο2 Eridani | 4.43 | 16.2 |
| Angetenar | τ2 Eridani | 4.76 | 190 |
| Zibal | ζ Eridani | 4.80 | 110 |
Distances are about, from the HYG database (Hipparcos parallax), and "not known" means the catalogue has no reliable parallax for that star.
How these facts were found
The name, meaning and boundaries are the IAU's. Area, borders and the latitude ranges are computed from those boundaries; the brightest star and the star count come from a magnitude-6 star catalogue; star names are matched to the catalogue by Hipparcos number and checked by position. The month is when Eridanus's middle crosses the north-south line of the sky at 9 pm local solar time. See How we know.
Sources
- IAU: The Constellations. Names, meanings, pronunciations and boundaries
- IAU Working Group on Star Names. The official names of stars
- astronomy-engine. The MIT licensed library that does the calculations, run on the page's build machine and in the app
- HYG database v4.4 (astronexus). Distances, spectral types and luminosities, licence CC BY-SA 4.0