The southern Poisson is small a Constellation of the Southern hemisphere. It is especially remarkable for its principal star, Fomalhaut (α PsA).

History

It seems that the constellation of the southern Poisson was already known under a similar name in the ancient Egypt. It is thus an old constellation which was indexed by Ptolémée in its Almageste . Its name of course makes during with the constellation Poisson, visible in the northern Hemisphere.

Observation of the sky

; Localization of the constellation The southern fish locates itself starting from its most brilliant star, Fomalhaut, which is located at the intersection of two great alignments.

• an alignment with very long distance, between Achernar with the South, and the Swan very far in North. This alignment leaves the wings of the Cygne, passes by the feet of PEGASE and the head of the Capricorne to reach Fomalhaut and from there Achernar.
• Another alignment, which starts from Aldébaran (α Tau), passes by the head and the tail of the Baleine, touches Fomalhaut and from there is prolonged on the head of the Centaure and the alignment of the bottom of Ophiuchus to finish on Arcturus in the Bouvier.

; Form constellation One can say, in a sense, that the constellation is reduced to a single star. The constellation has existence only compared to Fomalhaut, and the remainder does not have a very notable form. It is normal, for a fish, to be only guessed under water surface.

One can notice the first alignment appreciably NO - SE, in the medium of which Fomalhaut is. In fact, the star located at the SE of Fomalhaut is γ Sculpteur, therefore already in the close constellation.

More in the south, one sees an appreciably East-West alignment, who sets out again of γ of the Sculpteur, and passes by the pair δ γ PsA, then β, μ and ι PsA. This alignment is prolonged on ε and γ Microscope, much weaker.

; Close constellations Fomalhaut is surrounded by interesting constellations: The Capricorn in the North-West, the Aquarius in North, the Whale in the North-East, the Phoenix in South-east, and the Crane in the South. These constellations are located locally by their form and their vicinity, local alignments are not very suggestive.

Only notable alignment leaving Fomalhaut locally is alignment NO-SE of the " head of fish. This alignment thus passes by γ of the Sculpteur, and is prolonged to brilliant stars α, β and further δ from the Phoenix. In the south of the latter, one can see shining Achernar, final star of the Éridan.

Principal stars

See also: List of stars of the southern Poisson

Fomalhaut (α  Piscis  Austrini)

Fomalhaut (α PsA) - “ the mouth of the Arab Poisson ” in - is the most brilliant star of the constellation. With a magnitude connect of 1,17, it is also the 17th the most brilliant star of the sky.

Fomalhaut is a white star relatively near (24 light-years). It is surrounded by an immense disc of dust which extends on four times the distance from the Sun to Pluton.

Other stars

The other stars all of the constellation are considerably less brilliant than Fomalhaut. The second star, ε  Piscis  Austrini, reaches only magnitude 4,18.

Celestial objects

The constellation of the southern Poisson contains few notable celestial objects. One can however mention the Radiogalaxie IC 1549, the Spiral galaxy NGC 7314 and the barred spiral NGC 660.

See too

• List of stars of the southern Poisson

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