Eridanus (constellation)

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Eridanus
Image:Eridanus constellation map.png click for larger image
Abbreviation	Eri
Genitive	Eridani
Symbology	the river
Right ascension	3.25 h
Declination	−29°
Area	1138 sq. deg. Ranked 6th
Number of stars (magnitude < 3)	4
Brightest star	Achernar (α Eri) (App. magnitude 0.46)
Meteor showers	None
Bordering constellations	Cetus Fornax Phoenix Hydrus Tucana (corner) Horologium Caelum Lepus Orion Taurus
Visible at latitudes between +32° and −90° Best visible at 21:00 (9 p.m.) during the month of December

Eridanus is the sixth largest of the 88 modern constellations. It was also one of Ptolemy's 48 constellations.

At its southern end is the first magnitude star Achernar (α Eri). Achernar is a very peculiar star because it is one of the flattest stars known. Observations indicate that its radius is about 50% larger at the equator than at the poles. Responsible for this is the fact that Achernar is spinning extremely fast.

Another well-known star in Eridanus is Epsilon Eridani, which has been popular in science fiction because it is relatively close and relatively sun-like. It is now known to have at least one planet (see extrasolar planet), which is thought to be a gas giant, like Jupiter.

Mythology

Eridanus is associated with two greek myths, both likely to be derived from the shape of the constellation - that of very twisty path. Eridanus was sometimes considered to be a river which flowed from the waters of Aquarius, and in such situations, Aquarius was deigned to face Eridanus (requiring a change of angle, and thus redesign of how the stars of Aquarius connect, so that the water poured onto the same side as Eridanus).

Eridanus was more usually connected to the myth of Phaëton, who took over the reigns of Helios's (i.e. the Sun's) sky chariot, but didn't have the strength to control it, and so veered wildly in different directions. The result was that sometimes the chariot got too close to earth, creating desert and burning people's skin (a myth they considered to explain the skin of the Ethiopians). Zeus intervened by striking Phaëton dead with a thunderbolt. The constellation was considered, originally, to be the path Phaëton drove along, in later times, it was considered to be the river of the underworld that he fell into.

Stars

Stars with proper names:

(α Eri) 0.45 Achernar
< آخر النهر āxir an-nahr End of the river

(67/β Eri) 2.78 Cursa [Kursa] or Dhalim

(34/γ Eri) 2.97 Zaurak [Zaurac, Zaurack]
< زورق zawraq boat

(23/δ Eri) 3.52 Rana
(18/ε Eri) 3.72 Epsilon Eridani– nearby; has at least one planet, dust disk
(13/ζ Eri) 4.80 Zibal
< ? The ostrich

(3/η Eri) 3.89 Azha
(?) corruption of Persian آشيانه āšiyāne The (ostrich) nest

(θ Eri) Acamar – double 3.89, 4.35
< آخر النهر āxir an-nahr End of the river [named before Achernar was added]

(ο Eri)
- (38/ο¹ Eri) 4.04 Beid
  < بيض baiđ̧ eggs (of the ostrich)
- (40/ο² Eri) Keid [Kied] – triple 4.43, 9.5; nearby
  < ? al-qayd The (egg) shells
(2/τ² Eri) 4.76 Angetenar [Al Anchat, Anchenet, Hinayat (al Nahr)]
عوجة النهر ^{c^{awjat[u] an-nahr}} Bend of the river