The Piscis Austrinus constellation lies in the southern celestial hemisphere. Its name is Latin in origin which means “the southern fish.” We can use this name as a reference to its location in the night sky. Also, it separates itself from Pisces, a different constellation that also represents the fish.
Piscis Austrinus was one of the 48 classical Greek constellations included in the Almagest by Claudius Ptolemy. Today, it is still recognized as an official pattern in the sky. The International Astronomical Union (IAU) included it as one of the 88 modern constellations that we have.
It is the 60th largest constellation, occupying an area of 245 square degrees. As a whole, that is about 0.59% of our entire night sky. The IAU-approved abbreviation for Piscis Austrinus is PsA. We can use the genitive Piscis Austrini to refer to its stars.
Piscis Austrinus used to occupy a bigger spot in the night sky. However, the Dutch-Flemish astronomer Petrus Plancius carved out a part of it to form a different constellation. In 1597, the modern constellation of Grus (the Crane) was created out of that part. It is made up of the stars that used to form the tail of the sky’s Southern Fish.
People in the past have already recognized Piscis Austrinus and related it to their mythology. Its origin dates back to the Babylonian culture. They related it to their goddess Atargatis. Similarly, the Greeks and the Egyptians interpreted this constellation as a fish. They also have interesting mythological stories related to it.
Piscis Austrinus contains one of the brightest stars in our night sky. Its Alpha star, Fomalhaut, is the 18th brightest star that we can see up above. However, it is the only star in the constellation that is brighter than the third magnitude. Three of the stars in Piscis Austrinus are within the distance of 32.62 light-years from us. One of the three is the red dwarf Lacaille 9352, the eleventh nearest star system to us.
About six stars in the constellation of the Southern Fish have exoplanets. It has no Messier objects. Some of the notable deep-sky objects in it include the bright blazar PKS 2155-304. It has several known galaxies such as NGC 7174, NGC 7172, and NGC 7314. It contains SN 2009ip, a supernova discovered in 2009. A meteor shower has its radiant point in this constellation.
Piscis Austrinus is in the part of the sky that was known in earlier times as “the Water.” That same theme is the basis for the family of constellations where it belongs. It is in the Heavenly Waters family together with eight other constellations.
Heavenly Waters Family of Constellations
The constellations of Carina, Puppis, and Vela used to form the now-obsolete constellation of Argo Navis. Argo Navis was originally a very big Greek constellation. It represented the ship that Jason and the Argonauts sailed to search for the Golden Fleece.
What’s In A Name?
The Southern Fish was called by different names before it became Piscis Austrinus.
When the 2nd-century astronomer Claudius Ptolemy introduced Piscis Austrinus in the Almagest, he referred to it as Ἰχθύς Νότιος (Ichthys Notios). Although the name is in a different language, it means “Southern Fish.” Celestial cartographers Johann Elert Bode and Johann Bayer translated that name into Latin. They called it Piscis Notius. That name was used before the 20th century. Other names that Bayer associated with it are Piscis Meridanus and Piscis Austrinus.
Nicolas-Louis de Lacaille, a French astronomer who made great contributions in the study of the southern sky, called it Piscis Australis. The first Astronomer Royal, John Flamsteed, used the name Piscis Austrinus for this constellation. It appeared in his 1725 star catalogue and his atlas in 1729. The name caught on and remains so today.
This constellation is known to the Italians as Pesce Australe. The French call it Poisson Australe, while for the Germans it is Sudliche Fisch.
What Does Piscis Austrinus Look Like?
The boundaries of Piscis Austrinus are marked by four segments, just like a rectangle. It was set in 1930 by the Belgian astronomer Eugène Delporte.
Piscis Austrinus is commonly depicted as a fish that is lying on its back. It is relatively easy to spot because of the star Fomalhaut marking its mouth. The constellation’s pattern looks like a horizontal cone. Its upper part is the head of the Southern Fish and the tip is its tail.
In other sources, the outline of Piscis Austrinus is made up of more lines.
We can easily see a fish in this pattern. The small triangle definitely looks like a fish’s tail!
Pisces vs Piscis Austrinus: Which Is Which?
Piscis Austrinus is depicted as a fish with an open mouth. It is drinking the water poured from the jar of the water-carrier, Aquarius.
There is another fish-related constellation in our night sky, Pisces. So which is which? The very first difference between the celestial fishes is their locations. We already know that Piscis Austrinus is in the southern sky. Pisces is in the northern celestial hemisphere, so they are never the same.
Aside from location, they are also different in representation. Piscis Austrinus is just a single fish. Pisces, on the other hand, is nicknamed “the Fishes” because it represents two. These two fishes are tied together. It is also much bigger. While the “Southern Fish” is the 60th largest constellation, “the Fishes” ranks the 14th!
On top of that, Pisces belongs to the Zodiac family of constellations while Piscis Austrinus does not.
Where To See the Piscis Austrinus Constellation
Piscis Austrinus is in the 4th quadrant of the southern celestial hemisphere (SQ4). This constellation lies at about 22 hours right ascension and -30° declination. The negative sign indicates that it is south in declination. These equatorial coordinates tell us its position in the celestial hemisphere.
The Piscis Austrinus constellation is visible for observers here on Earth at latitudes between +55° and −90°.
Piscis Austrinus and Its Neighbors
Piscis Austrinus is surrounded by five constellations. Two of them are constellations of the zodiac, which means they are along the ecliptic.
Aquarius (the Water Bearer) is located to the north of the Southern Fish. Capricornus (the Sea-Goat) lies to the northwest. We can find Grus (the Crane) south of it, Microscopium (the Microscope) is to the southwest, and Sculptor (the Sculptor) is on the west side.
When To See the Piscis Austrinus Constellation
Piscis Austrinus is a seasonal constellation. It can be seen only during some time of the year because it dips below the horizon as it moves around the pole. Those that do not go below the horizon and can be seen all the time are called circumpolar constellations.
The Southern Fish can be seen during the autumn months in the northern hemisphere. During that time, about September to December, it is spring in the southern hemisphere. The best month to see it is during October, at about 9 pm.
Piscis Austrinus and Its Stars
About 47 stars in Piscis Austrinus have an apparent magnitude that is equal to or brighter than 6.5. Before they became what we know them now, they have undergone many changes in terms of designations. Some others became part of other constellations.
Its brightest star, Fomalhaut, was catalogued by Ptolemy in this constellation as well as in Aquarius. It was Johann Bayer that strongly defended that this star is only in Piscis Austrinus.
Originally, astronomers in the past assigned 12 stars in the constellation of the Southern Fish. The most notable stars in it were given the Bayer designations from Alpha to Mu. One of them was integrated into the Grus constellation. Now it is known as Gamma Gruis.
To polish things out, Nicolas Louis de Lacaille redrew the Piscis Austrinus constellation. He also relabeled the Bayer designations of its star after the reassignment of one star to Grus. Two stars, with the designations Tau and Upsilon, were added by Bode. More than 20 stars were given the Flamsteed designations.
Below are some of the prominent stars of Piscis Austrinus.
Fomalhaut (α Piscis Austrini)
Fomalhaut is called Alpha Piscis Austrini in the Bayer designation. Its Flamsteed designation is 24 Piscis Austrini. It is the brightest star in the constellation of Piscis Austrinus. Overall, it is the 18th brightest star in our night sky. A circumstellar disk surrounds this star. It is the third brightest star that we can see here on Earth after Pollux and the Sun.
The name of this star originated from the Arabic Fom al-Haut meaning “the mouth of the (Southern) Fish.” Though the name literally means “mouth of the whale.”
Fomalhaut is a wide-spanning triple star system. Its components are designated Fomalhaut A, B, and C. The third component belongs to the constellation of Aquarius.
Fomalhaut is an A-type star with an apparent magnitude of 1.16. The stellar classification of this main-sequence star is A3 V. It is 1.92 times as massive as the Sun and is more luminous by 16.63 times. It is located about 25.13 light-years from us.
One of the most notable features of this star is its debris disk. This disk emits infrared radiation. Its outermost disk is sometimes called “Fomalhaut’s Kuiper belt.” In 2008, the Hubble Space Telescope captured an extrasolar object orbiting inside one of its debris rings. It was designated Fomalhaut b, a candidate planet.
Fomalhaut is a relatively young star that is said to belong to the Castor Moving Group. The stars in this group share common velocities and directions. They are thought to be physically related, too. The bright stars Vega and Castor are in this group, together with Alpha Cephei, Alpha Librae, and many others.
Fomalhaut B (TW Piscis Austrini)
Fomalhaut B, or more commonly TW Piscis Austrini, forms a binary with the A-type star Fomalhaut. Its stellar classification is K5Vp.
TW Piscis Austrini is a BY Draconis variable. Its apparent magnitude varies from 6.44 to 6.51 in a period of 10.3 days. Its mass equates to 0.725 times the solar mass. It is about one light-year away from Fomalhaut. The two stars are about the same age, estimated to be 440 million years old.
Fomalhaut C (LP 876-10)
Fomalhaut C is the distant third component of the Fomalhaut star system. It is so distant that it is already in the neighboring constellation of Aquarius. The apparent magnitude of this star is 12.624. It belongs to the stellar class M4V.
LP 876-10 is about 2.5 light-years away from Fomalhaut A and 3.22 light-years distant from Fomalhaut B. It also has a dusty debris disk just like Fomalhaut A.
Beta Piscis Austrini (β Piscis Austrini)
Beta Piscis Austrini is a binary star. With an apparent magnitude of +4.29, is the fourth brightest star in the constellation of Piscis Austrinus.
The primary component is a main-sequence star with a white hue. Its stellar classification is A1 V. It is roughly 2.3 times as massive as the Sun. Its radius equates to 2.1 times the solar radius. The secondary star has an angular separation of 30.3″ from the primary. Its stellar classification is A2 V. Beta Piscis Austrini is 143 light-years away from our Sun.
Gamma Piscis Austrini (γ Piscis Austrini)
Gamma Piscis Austrini is another binary in the constellation of Piscis Austrinus. It moves through the Galaxy at a rate of 24.1 km/s. The primary star is chemically peculiar. Its stellar classification is A0 Vp(SrCrEu). This white-hued star has a mass that is 2.63 times that of the Sun’s. The other component is also a main-sequence star in the stellar class F5 V. Gamma Piscis Austrini is 215 light-years away from us.
Delta Piscis Austrini (δ Piscis Austrini)
Delta Piscis Austrini is a G-type star just like our Sun. We can see it with the naked eye as its apparent magnitude is +4.175. A companion was detected at an angular distance of 5.2 arc seconds. It is 9.86 in magnitude, much fainter than component A.
The stellar classification of the primary component is G8 III. Its mass equates to 1.42 times the solar mass. It is also more luminous by about 52 times. Delta Piscis Austrini is approximately 172 light-years distant.
Epsilon Piscis Austrini (ε Piscis Austrini)
Epsilon Piscis Austrini is a B-type star. It shines with an apparent magnitude of +4.17, making it the second brightest star in the constellation of Piscis Austrinus. The stellar classification of this blue-white hued star is B8 Ve.
Epsilon Piscis Austrini is a Be star. It is 4.1 times as massive as the Sun. Its radius measures about 3.2 times the solar radius. This fast-spinning star is radiating with a luminosity of 661 Suns. It lies approximately 400 light-years from Earth.
Zeta Piscis Austrini (ζ Piscis Austrini)
Zeta Piscis Austrini has a stellar classification of K1 III. It is suspected to be a variable star. It is more luminous than the Sun by about 61 times. This orange-hued star has an apparent magnitude of +6.43. It is roughly 413 light-years away from us.
Eta Piscis Austrini (η Piscis Austrini)
Eta Piscis Austrini is a binary star with an overall apparent magnitude of +5.43. The stellar classification of the primary component is B8 V. It is a Be star that spins rapidly. It is roughly four times as massive as the Sun. The other component is a fainter star with an apparent magnitude of 6.8. This star system is located 820 light-years away.
Theta Piscis Austrini (θ Piscis Austrini)
Theta Piscis Austrini is another multiple-star system in this constellation. The components of this binary are both +5.01 in apparent magnitude. They are also similar in stellar classification, A1 V. They orbit each other in a 20-year period. This star system is about 320 light-years distant.
Iota Piscis Austrini (ι Piscis Austrini)
Iota Piscis Austrini is a main-sequence star that is +4.35 in apparent magnitude. It belongs to the stellar class A0 V. It is approximately 204 light-year from our planet, Earth. This star has a faint visual companion that has an apparent magnitude of 11.4.
Lambda Piscis Austrini (λ Piscis Austrini)
Lambda Piscis Austrini is a B-type star as indicated in its blue-white hue. Its apparent magnitude is +5.42 so it is visible to the naked eye. This fast-spinning star is of B7 V spectral type. It is 3.58 times as massive as our Sun and 249 times as luminous. It is approximately 500 light-years away.
Mu Piscis Austrini (μ Piscis Austrini)
Mu Piscis Austrini is a single star that is about 122 light-years away from the solar system. It has an apparent magnitude of +4.49 so it is visible to the naked eye. Its stellar classification A1.5 IVn tells us that it is a subgiant star. It is oblate in shape as a result of its being a fast rotator.
Pi Piscis Austrini (π Piscis Austrini)
Pi Piscis Austrini is a single-lined spectroscopic binary. It is located near the border of the neighboring constellation of Sculptor. Its apparent magnitude is 5.12.
The stellar classification of the primary star is F1 V Fe-0.8. It is suspected to have a circumstellar disk because of the display of infrared excess. The other component’s stellar class is F3 V. The orbital period of the two stars is 178.3 days. This star system is 92 light-years from us.
Tau Piscis Austrini (τ Piscis Austrini)
Tau Piscis Austrini is an F class star on the main sequence. Its apparent magnitude is +4.9. It belongs to the stellar class F6 V. It is more massive than the Sun by about 1.34 times. Its radius is 1.45 times that of the Sun’s. It is 59.6 light-years away from Earth.
Upsilon Piscis Austrini (υ Piscis Austrini)
Upsilon Piscis Austrini is a star with an orange hue. It is in the stellar class K4 III. We can see it with the naked eye because its apparent magnitude is +4.98. It is a giant star that has undergone stellar evolution. Upsilon Piscis Austrini is part of the Wolf 630 moving group of stars. It is approximately 420 light-years from our planet.
S Piscis Austrini
S Piscis Austrini is a Mira variable. It is a pulsating red giant with a stellar classification of M3e-M5IIe. Its apparent magnitude varies from about 8.0 to 14.5.
V Piscis Austrini
V Piscis Austrini is also a variable star. Its magnitude ranges from 8.0 to 9.0 in a 148-day period. The spectral type of this red giant is M7/8III D. It is approximately 905.68 light-years from Earth.
Planets in the Southern Fish’s Constellation
Some stars in Piscis Austrinus were discovered to host exoplanets. Others have gas giants, like the one orbiting the F-type star WASP-124. Two gas giants were also discovered around HD 207832. The yellow-hued star WASP-112 has a Neptune-like companion. Below are other exoplanets in the constellation of the Southern Fish.
Fomalhaut b is a controversial extrasolar planet. It orbits around the star component A in the triple star system of Fomalhaut. Although it looks like a tiny dot (pointed by the arrow in the photo above) next to its gigantic star, it is actually nearly the size of two Jupiters. It orbits the A-type star in a period of 872 years. The IAU-approved name for this exoplanet is Dagon, after a Semitic deity that is half-man, half-fish.
GJ 887 b
Lacaille 9352 b, or more commonly GJ 887 b, is a potentially rocky super-Earth. Its mass equates to 4.2 times our planet’s mass. It is 0.068 AU from its red dwarf star, orbiting it in a period of 9.3 days. This planetary system is about 11 light-years away from us.
GJ 887 c
GJ 887 c is a gas giant that is comparable to Neptune in size. It is as massive as 7.6 Earths combined. It is 0.12 AU from the star M-type star. GJ 887 c completes an orbit around it in 21.8 days. It is closer to the habitable zone of its planetary system than GJ 887 b.
HD 205739 b
HD 205739 b is a giant exoplanet that is 302 light-years from Earth. This gas giant has a mass of 1.37 Jupiters. It orbits its white-hued star in a period of 279.8 days. It was discovered in 2008.
HD 216770 b
HD 216770 is another gas giant in the constellation of Piscis Austrinus. Its mass equates to 0.57 Jupiters. It is 0.46 AU from its G-type star and orbits it in 118.5 days. This planetary system is 120 light-years from Earth.
Deep-sky Objects in Piscis Austrinus Constellation
Many galaxies were discovered in Piscis Austrinus. An example of this is the edge-on spiral galaxy NGC 7172 which is 11.9 in magnitude. This constellation also hosts the bright blazar PKS 2155-304.
NGC 7173, NGC 7174, and NGC 7176
The galaxies NGC 7173, NGC 7174, and NGC 7176 three interacting galaxies. NASA describes them as “playing a game of gravitational tug-of-war.” They are part of the Hickson Compact Group 90, after the astronomer Paul Hickson. The interaction of these three galaxies will most likely reform them into two, with only the elliptical galaxies NGC 7173 and NGC 7176 remaining.
The gravitational pull of the interaction already has its effect on NGC 7174. Its stars are said to be ripped away from this galaxy and are now spread out.
NGC 7259 is another spiral galaxy in Piscis Austrinus. English astronomer John Herschel discovered it in 1834. The supernova SN 2009ip was detected in it in 2009. This galaxy is approximately 66 million light-years away.
NGC 7314 is a spiral galaxy with a weak central bar. It has an active galactic nucleus, a type I Seyfert. It has a supermassive black hole in its center. This galaxy is 54.6 mega light-years from our galaxy, the Milky Way.
Meteor Showers Related to Piscis Austrinus
A meteor shower originates from the constellation of Piscis Austrinus. It is called the Piscis Austrinids.
The Piscis Austrinids has its radiant point west of the star Fomalhaut. The shower takes place every year from July 15 to August 10. The peak occurs on July 28. It can be best observed from the southerly latitudes. The zenith hourly rate, or the number of meteors we can expect to see per hour, is five.
Mythology Related to Piscis Austrinus Constellation
The earliest mythological associations of Piscis Austrinus can be traced back to the Middle East. It had been related to the lives of the gods and goddesses of Syria, Greece, and Egypt. Although some of the accounts are rather sketchy and incomplete, they still give us some idea of the people’s beliefs in the past.
Piscis Austrinus was called MUL.KU in Babylonia. The name of this Babylonian constellation simply means “the Fish.” It was mentioned in the mythological story of a chief goddess of Syria. Her name was Atargatis (Derceto in Greek), the fertility goddess.
Atargatis was a goddess of fertility. One day, she accidentally fell into a lake at Hierapolis Bambyce. The said lake is near the Euphrates in Syria. A big fish saved the goddess. And from that, the fish was placed in the night sky. They believed that it is the parent of the two fish in the Pisces constellation.
It was said that because of that event, Syrians started to worship the images of fish. The same story is used as a reference to their practice of abstinence from eating it.
A different story explains the Syrian’s abstinence from fish. According to these classical sources, temples of the goddess Atargatis have ponds that house sacred fish. Atargatis ordered that nobody should eat fish and that whoever defies her would become ill. The only ones allowed to eat fish are her priests, during theophagy or “god eating.”
There is another fish-related story that involves Atargatis. It was said that she fell in love with a younger man named Caystrus. She bore a child out of that affair. Because of shame, she jumped into a lake hoping to run away from what she did. However, she became half human and half fish. She developed a tail just like a mermaid but her head remained human. She abandoned her baby and took the life of the young Syrian man. The baby was saved and brought up by doves. She grew up and was named Semiramis. She would later be known as the Assyrian queen.
The Great Fish of the constellation Piscis Austrinus was said to be the parent of the two fish in Pisces constellation. The story related to it in Greek mythology involves that of Aphrodite and her son, Eros.
Aphrodite and Eros were fleeing from the monster Typhon. They came to the river Euphrates, the longest river in Syria. Aphrodite asked for help from river nymphs and jumped into the river, fearing that Typhon was near. Help came in the form of two fish that bore them up. Aphrodite thanked them by placing them in the heavens in the form of constellation Pisces. And because of the good deed of the said creatures, the Syrians did not eat fish.
The Egyptians had a somewhat similar story of how the Southern Fish came to be. According to their mythology, a fish saved the life of Isis. The goddess Isis was an important figure in Egyptian mythology. She honored the fish that saved her life by placing it in the sky as Piscis Austrinus. She did not forget its offsprings and laid a place for them in the heavens as well. The two formed the Pisces constellation.
More About Piscis Austrinus
Piscis Austrinus appeared in many celestial charts and atlases, one of such is in Urania’s Mirror.
Urania’s Mirror, or a view of the Heavens, is a set of star charts. The set came in 32 celestial cards that were published in 1824. On these charts are colorful depictions of the constellations in the night sky. What made Urania’s Mirror more exciting is that holes were punched on them. We can see that these holes serve as the stars in a constellation. That is done by holding the chart up against a light.
Piscis Austrinus was depicted on Plate 26 of Urania’s Mirror. Together with it are Aquarius and the now-obsolete constellation of Ballon Aerostatique. The Southern Fish was cut off in that star chart. However, we can still see it at the end of the flow of water poured by Aquarius.
The other constellation in the chart, Ballon Aerostatique, is the equivalent of “hot air balloon” in French. Another name for it is Globus Aerostaticus in Latin. The constellation was created in 1798 by the French astronomer Jérôme Lalande. It was invented in honor of the Montgolfier brothers.
Ballon Aerostatique would have been a close neighbor to Piscis Austrinus if it is still used to this day. It used to be located in the area between Capricornus, Microscopium, and Piscis Austrinus.