The constellation Southern Fish (Piscis Astrinus-PsA)

The Southern Fish

THE NAME, THE HISTORY, THE MYTH


The Southern Fish was well known in ancient Greece, and with a shape quite similar to the one we know. The mythology of the entire constellation was often included in that of its brightest star, Fomalhaut. Although it lies well below the ecliptic, Fomalhaut is the brightest star in this celestial region, which allows it to serve as a reference for the "seasonal movement" of the sky. It is therefore not surprising that it was indicated as one of the four Royal Stars or "Celestial Observers" identified in ancient Mesopotamia (the others are Regulus- alpha Leo-; Aldebaran -alpha Tau; Antares -alpha Sco-).


The figure in its entirety, and Fomalhaut in particular, have been frequently identified with the zodiacal constellation of Aquarius, completing a cross of four celestial signs, Taurus, Leo, Scorpio, Aquarius.

In the book The New Patterns in the Sky (" the new models of the sky") the astronomer Julius Staal (1917-1986) brings back the origin of the Southern Fish to Egyptian mythology, as Igino also reported. The god-king Osiris, who is said to have introduced civilization in Egypt, was assassinated by his brother Set, who was jealous of him. He dismembered the body of Osiris into 14 parts, which he threw into the Nile. Isis, wife and sister of Osiris, searched and found all the parts except one, the phallus, which was swallowed by the Nile Oxirynchus crab, identified in the constellation of the Southern Fish, which swallows the waters of life. In reference to the myths of the Dilivio, the act of swallowing water poured from the jug of Aquarius has been interpreted as a symbol of salvation from the flood.


The Southern Fish has also been seen as the parent of Pisces.

It has Middle Eastern origins, however, legend has it that Derceto, goddess of fertility, decided to commit suicide by drowning in a lake near the Euphrates (in a different version he fell into the lake) after giving birth to a little girl, Semiramis, who came into the world from a forbidden relationship with a mortal. The goddess was saved by a fish - although other legends speak of transformation into a mermaid - and as a sign of gratitude she wanted to put it in the sky.

This constellation is also known as 'Lonely Fish' and another legend has it associated with the Syrian god-fish Oannes, who came to Earth to civilize the barbarian men.

The Southern Fish constellation

The constellation is so called in order not to confuse it with that of Pisces, especially when we read for example that "α PsA is called Fomalhaut": in Latin the constellation is Piscis Austrinus (to the genitive piscis austrini). I have quoted the name of its brightest star, a beacon of magnitude 1.15 in a zone of sky particularly poor of bright stars, because it is perhaps the first star name I have ever learned. I find this name very fascinating and I've always heard it pronounced and heard it pronounced reading it as it is and not as someone on TV some time ago said something like "fomlùt"... maybe he thought it was German, but it's actually Arabic and the term means fish mouth.



Clicking on the animation will open as usual the 3D applet of the constellation where we can immediately click on "f" to see the representation of H.A.Rey, much better than the official one, that everything seems less than a fish. Turning the virtual sheet with the right and left arrows we can see that just Fomalhaut has a very low distance in al, but as we will see there is another star even closer.

The constellation is ancient so its representation is found both in the Uranometria

the Southern Fish in Uranometry

that in Hevelius' work

the Southern Fish according to Hevelius

in addition to the usual Stellarium.

the Southern Fish according to Stellarium

Two stars nearby

The nearest star is Lacaille 9352 (also known as HIP 114046 or Gliese 887 or Cordoba 31353, depending on the star catalogue in which it is inserted), a red dwarf of spectral class M0, half the size of the Sun, placed at the small distance of 10.69 al, in 14th place in the list of the nearest stars. If we go to the parts of the star by means of Celestia, or going to visit my Lacallian friends, looking towards our Sun, we find it quite bright in a decidedly boreal zone of sky, among stars of the Big Bear and the Lesser Lion, for once without other illustrious and near stars (like Sirius): my friends, poor things, suffer a lot, having 4 pairs of legs and relative feet. Nobody has ever pointed out to them that many of their problems would be solved with bigger shoes, but from this ear they can't hear us, also because they don't have any.


But let's move on to Fomalhaut, which is better. We know about its brightness and now I add that its spectral class is A3 and that it is only 25 al from us, where "barely" has its meaning only if we compare it to other stellar and galactic distances, but certainly not absolutely, on an Earth scale. My Fomulaùni friends know something about it. They are very fond of car races and they would pretend to reach our Sun on board spaceships in the shape of a single-seater with 4 wheels, useful for landings: they haven't yet found a tank big enough to contain fuel, but in the meantime they run all day with their helmets on their heads, because that's how they are used to. Our Sun seen by them is decidedly less bright and it is in the same area of the previous sky, with the inclusion of other known stars, such as those of Leo (Regulus and Denebola, but also Zosma and Algieba).

Some big stars

comparison between the stars of the Southern Fish and other notes

From the usual diagram of comparison between the stars of the Southern Fish and other monsters of the sky one cannot but notice the umpteenth defeat of Aldebaran: the biggest star of the constellation, 13 PsA an orange giant of class K5, has a diameter equal to 97 times that of the Sun and in fact almost 3 times round that of the bright star of Taurus, which is receiving fishes in the face from at least one star of each constellation. My friends Tredicipsi sent me the photo of their 10 UA star, as always dazzling and disturbing from an enormous distance, such as Saturn from the Sun.

The second big star is a red giant of class M3, 19 PsA, with a radius 69 times that of the Sun: I couldn't get in touch with my friends Ticiannovìpsi, who have big problems with ADSL and telephone operators (how strange!).

The last star for physical size is the PsA υ, of spectral class K4, which with a ray equal to 36 times that of our Sun is practically a twin of Aldebaran: since it is located at 527 al, it does not have the notoriety of the brightest star of Taurus, which instead is only 65 al. My Upsìpsi friends, aware of this fact, have recently formed a twinning relationship with the Aldebarans, ready to shake their 14 hands as a sign of stellar brotherhood, as soon as their friends arrive in their neighbourhood.

Let's give up the facetiousness and observe the...

Deep sky objects

Few objects, but very interesting. The first one I propose you is actually triple and is formed by three galaxies, NGC 7173, NGC 7174 and NGC 7176, in an interaction that (I read, but I don't have enough confirmations, so I give you the news as a curiosity) will bring them to a fusion in a single object

the interaction between three galaxies

the second object is a spiral galaxy, NGC 7172

the beautiful galaxy NGC 7172

while the last object is another spiral galaxy, NGC 7314

the beautiful galaxy NGC 7317

Names and visibility

The only star to have received a name is the repeatedly quoted Fomalhaut whose name is (apart from the wrong pronunciations) widely used by Astronomers.

The constellation of the Southern Fish is well visible at our latitudes at 9 p.m., the time I have chosen for our observations: it begins to appear low on the horizon in the last decade of August, culminating in the South, at the meridian at the end of October (with Fomalhaut shining at 20° on the horizon). We find it low on the horizon in the first days of December.

On summer evenings and nights, when just before mid-August you are nose-up looking for the shooting stars of S.Lorenzo (the Perseids), around midnight you look southeast: you can see Fomalhaut rising and moving south and you will immediately recognize it for its brightness.



Audio Video The constellation Southern Fish (Piscis Astrinus-PsA)
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