Éridan (constellation)

See also: Éridan

The Éridan is a Constellation of the Southern hemisphere, located at the accesses of Orion, Taureau and male Hydre. It is the sixth constellation of the sky from its size (1 138 square degrees), it contains 300 stars - including three of magnitude lower than 3 - mainly laid out according to a long sinuous line, with the manner of a river.

By its size, it is at the same time an equatorial and circumpolar constellation of the southern hemisphere.

History

This Constellation of the southern hemisphere owes its name with a river of Greek mythology. It is said sometimes that it would be about the Po. It was indexed for the first time at the first front century J. - C. by Ptolémée, but it is William Herschel which catalogued it in 1783. It finished formerly in Acamar.

Observation of stars

Éridan is hardly visible, and is rather difficult to trace. Its two principal stars mark the two extremities of them:

  • β Eri (Cursa) is located at the feet of Orion, in the equatorial zone.
  • Achernar (α  Eridani) is insulated and very brilliant, in the practically polar southern zone. Isolated and brilliant, it is an important reference mark of alignments in the southern hemisphere, but which cannot be identified by the local form of the constellations, nor by its alignments.

; Form constellation β Eri (Cursa) is located at ~4° in the north of Rigel, the Western foot of Orion. On the basis of β Eri (Cursa), the river runs appreciably towards the West, in a zone where one notices especially γ Eri (Zaurac), the brilliant star (mag 3) with a score of degrees OSO of Rigel. Starting from Zaurac, the river still makes a vast loop until the limit of the Baleine, a score of degrees more in the west, then returns towards the East along a vast chain formed by τ1 to τ9 Eri. All the zone included/understood in this northern loop belongs to the constellation.

The continuation of the constellation starts from ν1 and ν2 Eri, a small pair of stars appreciably in alignment SO between Rigel and the ears of the Lièvre to the feet of Orion. In same alignment, one finds a little further ν3 and ν4 Eri, another small appreciably west-east directed pair. While continuing towards the SO, one falls on a very weak small triangle, formed by F (southern) G (northern) and H (western) Eri. This triangle (which is located at the limit of the Fourneau, more in the West) mark limit between the northern zone and the southern zone of the constellation.

From this limit, the river runs appreciably towards south-west, until Achernar, while threading between the generally weak close constellations: the Furnace in the west, in its last meander, then the Phoenix much more visible; east coast the Graver, and the Clock.

; Alignments with long distance Achernar is an important pole in celestial alignments, from which start from very many alignment.

Principal stars

See also: List of stars of Éridan

Achernar (α  Eridani)

Achernar (α  Eridani), magnitude connects 0,46, is the 8th the most brilliant star of the vault of heaven. Its name comes from an Arab sentence meaning the mouth of the river , which characterizes it perfectly because it closes the southern end of the constellation. Consequently, it is never visible beyond 30° of northern Latitude and never is seen better than starting from the Tropique S.

Distant of 144 light-years, Achernar is a very hot star (of which the temperature of surface east close to 20.000 K, approximately 7 times larger than the Sun.

According to observations of VLT (Broad Very Telescopes), it would seem that because of its very fast rotation (it turns to 225 km/s to the equator), this star is a Ellipsoïde whose equatorial Diamètre is the double of the polar diameter.

Acamar (θ  Eridani)

Acamar (θ  Eridani) marked in the beginning the end of the constellation and its name derives, like that of Achernar, of an Arab sentence meaning the end of the river . Besides it bore the name of Achernar to the Moyen-âge.

It is a star doubles: θ1  Eridani is a blue Géante, θ ²   Eridani is a blue Naine.

Other stars

Zaurak (γ  Eridani) is a Géante red whose real glare is worth 300 times that of the Sun (absolute magnitude: -1,19). Its distance of 220 light-years confers a magnitude to him connect of 2,97. Rana (δ  Eridani), a little colder than our star but 2,7 times more brilliant than it, is located at 29,4 light-years. Apparent magnitude: 3,70; absolute magnitude 3,74.

Because of size of the constellation, much of others of its stars bear a proper name: Cursa (β  Eridani), Zibal (ζ  Eridani), Beid (ο1  Eridani) and Keid (ο ²   Eridani), Angetenar (τ ²   Eridani), Theemin (υ ²   Eridani), Sceptrum (HR  1481) and Azha (η  Eridani)

ε  Eridani is the 10th star nearest to our Solar system and resembles the Sun much. It has at least a planet.

Celestial objects

The constellation of Éridan contains the Nébuleuse planet gear NGC 1535, distant 2.200 years light and magnitude 9,60 connect and the barred spiral galaxy NGC 1300, of type SBc, sight of 3/4 and magnitude 10,8.

An area of the cosmological diffuse Fond located in the direction of this constellation presents a fluctuation of important Température in the context of the standard Modèle of cosmology. It is called Point cold. It could be a question of an area relatively not very dense in Galaxies.

See too

  • List of stars of Éridan

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