See also: Poisson (homonymy)

The Poisson are a Constellation Zodiaque crossed by the Sun of the March 12th to the April 18th. In the order of the zodiac, it is located between the Verseau at the west and the Bélier at the east. Although enough large, it cuts out a side of the sky far away from the plan of the Milky Way and contains only few visible stars, all rather not very luminous.

The Poisson are also a sign Zodiaque corresponding to the sector of 30° of the ecliptic crossed by the Sun of the February 19th to the March 20th.

History and mythology

The constellation of Poisson is one of the oldest constellations. Its origin probably goes up with the Babylonian which already described it like made up of two fish pushing a giant egg (asterism of “the Ring”).

The Greek Mythologie wants that these fish are the forms assumed by Aphrodite and Eros continued by the monster Typhon. They would have connected their tails with cord in order not to separate. Besides the old sky charts name the oriental party Piscis Boreus and the Western part Piscis Austrinus (which have nothing to do with the southern Poisson contemporary).

The point " gamma" , the solar ascending node, that occupies the Sun at the time of the equinox of spring, is currently with 8° in the south d'ω  Piscium. However, because of the phenomenon of Precession of the equinoxes, this point was in the Bélier during the last two millenia before J. - C., i.e. at the time when the Zodiaque was establishes. Consequently, Poisson are always regarded as the last sign of the zodiac (the year started then towards the vernal equinox) although they are from now on the first.

Observation of stars

; Localization of the constellation This constellation is in the immediate vicinity of the Grand square of PEGASE, from which it can be located if the conditions of visibility are sufficient.

These conditions of visibility are seldom good, like the majority of the water constellations of this area, Poisson live hidden most of the time under surface.

; Form constellation

• the ring of Poisson is located 10° at the South of the edge of the great square. It is an oval structure, marked rather well but not very luminous (mag 5). If this ring is visible, one can also guess an alignment which leaves there towards the East (the Western cord), and follows an arc of circle while curving towards the South, until α  Piscium, the node of the two cords.
• the other ring is much more difficult to locate, because its form is less clear, and it merges with the southern arm of Andromède. When this arm is quite visible, one can see it finishing on an alignment of three weak stars, of which more in the South is the elbow of the cord Is, immediately in the East of the great square. On the basis of this elbow, one finds another small alignment which limits the ring Is (which resembles a triangle rather). In the other direction, the prolongation of the arm of Cassiopée indicates the head office of the cord, which slips by until α  Piscium, the node of the two cords.

; Location starting from Poisson The weakness of the constellation does not encourage to seek alignments at long distance there, but the node of the two cords is very useful in what in the prolongation of the cords, after an additional jump of 6°, one falls on Mira Ceti, most famous of variable stars. Reflected is a variable of which the period makes 332 days, and who passes from a magnitude of 2 (dominating the area) to magnitude 9 (invisible with the naked eye) in an appreciably Log-sinusoidal way. It is thus visible half of time.

Principal stars

See also: List of stars of Poisson

η  Piscium

The most brilliant star of the constellation of Poisson, η  Piscium, does not have a proper name and reaches only the Magnitude connect 3,62. It is a yellow giantess, 25 times larger than the Sun and 4 times more massive. She has a companion which one does not know the composition distant of 70 ua.

Alrisha (α Piscium)

The star α  Piscium is called Alrisha, of an Arab sentence meaning “the Node” in the cord which connects two fish. Of a magnitude connect of 3,82, it most brilliant, is not preceded by η  Piscium and γ  Piscium.

It is in fact a double star, made up of two distant white stars one of the other of 120 ua on average. Most brilliant is Alrisha-A with an apparent magnitude of 4,33. Alrisha-B reaches magnitude 5,23. It seems that each one of them is also double.

Other stars

γ  Psc, 7  Psc, θ  Psc, ι  Psc, λ  Psc and κ  Psc compose a Astérisme called “the Ring”. γ  Psc is the 2nd star of the constellation with a magnitude of 3,70. It is a yellow giantess, distant from 130 light-years.

Two other stars of the constellation bear a name: Fum Al Samakah (β  Psc) and Torcularis Septentrionalis (ο  Psc).

The star of van Maanen, located a few degrees in lower part of δ  Psc, is the 31e star nearest to the Solar system. It is a white Naine distant 14,06 years light.

Celestial objects

The constellation of Poisson counts two spiral galaxies: M74 (a Radiogalaxie) and NGC 676.

See too

• List of stars of Poisson

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