Piscis Austrinus
“The Southern Fish” · Southern · best around October evenings
Real star positions and magnitudes (HYG database via D3-Celestial, BSD-3). Lines are the conventional stick figure; north is up.
The story
The parent fish of the zodiac pair, drinking the water Aquarius pours. Solitary Fomalhaut — 'the mouth of the fish' — is the loneliest first-magnitude star, ringed by a vast debris belt Hubble and JWST have imaged in detail.
How to find it
The bright lone star low in northern autumn skies.
✦ What lives inside it
The deep dive
Researched for the Atlas from Wikipedia — Piscis Austrinus (8,038 characters read) · updated Sep 20, 2026
01 A constellation older than Greece itself
Piscis Austrinus did not originate with the Greeks who eventually adopted it. Its roots lie in Babylonian sky-lore, where it was recorded simply as the Fish, written in cuneiform as MUL.KU. Professor of astronomy Bradley Schaefer has argued that ancient observers must have traced the pattern as far south as the star Mu Piscis Austrini to construct a shape that genuinely resembled a fish — and that star is explicitly mentioned in Ptolemy's Almagest, confirming the figure was a direct inheritance from Babylon rather than a Greek invention. The constellation arrived in the Greek world around 500 BCE, entering alongside Aquila the eagle, Corvus the crow, and Hydra the water snake. That particular group of four was not chosen at random: together they marked the summer and winter solstices of the era, giving them a practical calendrical importance far beyond their stories. By the time Ptolemy compiled his Almagest in the 2nd century CE, Piscis Austrinus was fully established as one of his canonical 48 constellations, a list that survived as the backbone of Western astronomy for over a thousand years.
02 Three cultures, one fish in the sky
The same star pattern collected strikingly different stories depending on where the storyteller lived. In Greek tradition the fish was cast as the Great Fish, dramatically swallowing the stream of water poured down by Aquarius the water-bearer directly above it. The two fish of Pisces were said to be its offspring, weaving the constellations into a family narrative across the southern sky. Syrian tradition attached the figure to a far more specific local legend: the Greek historian Ctesias, writing in the 5th century BCE, recorded that this fish had lived in a lake near Bambyce in Syria and rescued Derceto, daughter of Aphrodite herself, from drowning. As a reward it was lifted into the heavens, and the gratitude was so deep that fish were considered sacred and went uneaten by many Syrians. Egyptian mythology offered yet another rescue story: here the fish saved the goddess Isis, and in return she immortalized it and its descendants among the constellations. Three completely independent cultures therefore looked at the same faint stars and independently saw a creature deserving divine reward.
03 How Piscis Austrinus lost its tail
The constellation we see on modern charts is a shrunken version of what ancient astronomers recognized. The stars that now form the separate constellation Grus — the crane — were once considered the tail of Piscis Austrinus, giving the fish a much more extended southern sweep. That changed in 1597 or 1598, when the Dutch cartographer Petrus Plancius carved those tail-stars away and named the new figure after the crane. Similarly, some stars near the fish's northern edge were absorbed into the newly defined Microscopium. Even within the core group, ancient astronomers counted twelve stars as belonging to Piscis Austrinus, and one of those — now known as Gamma Gruis — was formally reassigned to Grus. The boundary shuffling continued into the 19th century: the astronomer Lacaille redrew the constellation because it was poorly visible from Europe, adding stars labeled nu and pi and reshuffling the Greek-letter designations of gamma, delta, and epsilon. Later, Baily dropped nu as too dim, while Bode added tau and upsilon. The official modern boundaries were finally fixed by Belgian astronomer Eugène Delporte in 1930.
04 Fomalhaut: a star with a complicated companion Deeper
Fomalhaut dominates Piscis Austrinus so completely that the constellation is often summarized as little more than a frame for it. With an apparent magnitude of 1.16, it ranks as the 18th-brightest star in the entire night sky and is the only star in the constellation brighter than 4th magnitude. It sits 25.13 ± 0.09 light-years from Earth — close enough that its properties are measured with real precision — and is a white main-sequence star 1.92 ± 0.02 times as massive as the Sun and 16.63 ± 0.48 times as luminous. Its circumstellar disk made it an early and celebrated target in the search for planetary systems. The object designated Fomalhaut b generated enormous excitement when it appeared to be the first extrasolar planet ever imaged directly in visible light, captured by the Hubble Space Telescope. That claim did not survive scrutiny: subsequent infrared observations failed to confirm it, and the consensus shifted to interpreting the object as a spherical cloud of dust rather than a planet, making the story a cautionary tale about how difficult direct planet detection genuinely is. A possible true planet may still orbit within the disk, but the article is careful not to overstate the case.
05 TW Piscis Austrini: Fomalhaut's possible neighbor Deeper
Visible close to Fomalhaut on the sky is a star called TW Piscis Austrini, and the proximity may not be purely a line-of-sight coincidence. The star lies within a light-year of Fomalhaut in three-dimensional space, raising the possibility that the two are physically associated — perhaps gravitationally bound as a very wide binary, or at minimum formed from the same cloud of gas. TW Piscis Austrini is classified as a BY Draconis variable, a category of star whose brightness fluctuates because starspots — dark, magnetically active regions analogous to sunspots but often covering much larger fractions of the stellar surface — rotate in and out of view as the star spins. Its apparent magnitude is 6.5, placing it right at the threshold of naked-eye visibility under excellent conditions but more reliably caught with binoculars. The question of whether it truly shares an origin or orbit with Fomalhaut remains open; the article presents the association as a possibility rather than a confirmed physical relationship, which is an honest summary of a genuinely uncertain situation in stellar astronomy.
06 A red dwarf next door with two super-Earths
At just 10.74 light-years away, Lacaille 9352 is one of the Sun's nearest stellar neighbors, and it falls within the boundaries of Piscis Austrinus. It is a red dwarf of spectral type M0.5V with less than half the Sun's diameter and mass, and despite being one of the brightest red dwarf stars in the night sky it still only reaches magnitude 7.34 — firmly below naked-eye visibility. In June 2020, astronomers using the radial velocity method detected two super-Earth planets orbiting it. Super-Earths are a category with no analog in our own solar system, with masses between those of Earth and Neptune, and their discovery around such a nearby star makes Lacaille 9352 a scientifically significant target. The radial velocity method works by detecting the tiny wobble a planet induces in its host star as it orbits, revealing its presence through subtle Doppler shifts in the star's light. Because the star is so close — only about 2.5 times the distance to Alpha Centauri — future characterization of these planets may be more achievable than for worlds around more distant stars.
07 A galaxy family and an impostor supernova Deeper
Piscis Austrinus contains several deep-sky galaxies accessible to amateur telescopes. NGC 7172 and NGC 7314 are listed alongside a third galaxy, carrying magnitudes of 11.9, 12.5, and 10.9 respectively, making the brightest of the trio a feasible target for a medium-aperture telescope under dark skies. NGC 7259 is another spiral galaxy within the constellation's borders, and it drew attention in 2009 when it hosted the event catalogued as SN 2009ip. That event was originally classified as a supernova, but SN 2009ip has since become one of the more debated objects in transient astronomy — its behavior proved unusually complex and prolonged, leading researchers to question whether the star actually exploded terminally or survived as an erupting luminous blue variable. The article records it as a supernova without detailing the subsequent controversy, but even the basic fact of a supernova-class event in a magnitude-12.5 galaxy in this modest constellation illustrates that even obscure corners of the sky occasionally produce phenomena that recalibrate how astronomers understand stellar death.
08 PKS 2155-304: a blazar in the fish Deeper
Among the most extreme objects hiding within Piscis Austrinus is PKS 2155-304, a BL Lacertae object classified as one of the optically brightest blazars in the entire sky. A blazar is a type of active galactic nucleus — a supermassive black hole at the center of a distant galaxy that is actively consuming material and firing a relativistic jet of plasma directly, or nearly directly, toward Earth. BL Lacertae objects are a subclass characterized by rapid, irregular variability and featureless optical spectra. PKS 2155-304 sits at a redshift of z = 0.116, which places it at a cosmological distance that dwarfs anything else in the constellation. For reference, the galaxies NGC 7172 and NGC 7314 are comparatively nearby; PKS 2155-304 is genuinely extragalactic on a grander scale. Despite that distance it remains one of the brightest blazars visible in optical light, a consequence of its relativistic jet being beamed almost straight at us, effectively amplifying its apparent brightness far beyond what its intrinsic luminosity alone would produce.
09 A constellation of many names
Few constellations have accumulated as many official-sounding aliases as Piscis Austrinus. Ptolemy called it Ichthys Notios — Greek for Southern Fish — in the Almagest. When that text was transmitted into Latin-language astronomy, it became Piscis Notius, the name used by the German celestial cartographers Johann Bayer and Johann Elert Bode. Bayer also applied two additional Latin names to the same figure: Piscis Meridianus and Piscis Austrinus. French astronomer Nicolas-Louis de Lacaille settled on Piscis Australis. The English Astronomer Royal John Flamsteed chose Piscis Austrinus, and because Flamsteed's catalog was enormously influential, that version stuck and became the modern standard. The International Astronomical Union formalized the three-letter abbreviation as PsA in 1922. Before the 20th century the name Piscis Notius still circulated widely enough to be considered an acceptable alternative. The constellation occupies a relatively compact area of sky, with right ascension borders running from 21h 27.3m to 23h 06.5m and declination coordinates between −24.83° and −36.46°, and it is fully visible to any observer south of latitude 53°N.
10 Exoplanet systems hiding in a faint constellation Deeper
Beyond Lacaille 9352 and the contested case of Fomalhaut b, Piscis Austrinus harbors confirmed exoplanet systems around at least five additional stars. HD 205739 is a yellow-white main-sequence star of spectral type F7 V hosting a planet roughly 1.37 times as massive as Jupiter with an orbital period of 279 days, and evidence hints at a second planet. HD 216770 is an orange dwarf with a Jupiter-like companion completing one orbit every 118 days. HD 207832, a G5V star with about 90% of the Sun's diameter and mass and around 77% of its luminosity, was found in 2012 to host two gas giants via the radial velocity method: the inner planet has about 56% of Jupiter's mass and orbits at a mean distance of roughly 0.57 astronomical units with a period of 162 days, while the outer planet carries about 73% of Jupiter's mass, orbits at around 2.11 astronomical units, and takes 1,156 days to complete one circuit. Two additional stars, WASP-112 and WASP-124, are sun-like stars whose planets were found by the transit method. Together these systems make Piscis Austrinus a surprisingly productive hunting ground for planetary science.
11 The variable stars: from days to centuries of change Deeper
Piscis Austrinus contains variable stars spanning a striking range of timescales and physical mechanisms. S Piscis Austrini is a Mira-type variable, meaning it is a cool, pulsating red giant whose radius swells and shrinks over a period of 271.7 days. Over that cycle its brightness ranges from magnitude 8.0 down to 14.5 — a factor of more than 400 in luminosity — making the difference between a reasonably accessible binocular target at peak brightness and something requiring a moderate telescope near minimum. V Piscis Austrini is a semi-regular variable, a category where the periodicity is real but imprecise, oscillating between magnitudes 8.0 and 9.0 over approximately 148 days. Epsilon Piscis Austrini, the second-brightest star in the constellation at magnitude +4.17, is a blue-white main-sequence star located 400 ± 20 light-years away, 4.10 ± 0.19 times the Sun's mass and about 661 times its luminosity. Delta Piscis Austrini is a double star with components of magnitude 4.2 and 9.2; the brighter is a yellow giant of spectral class G8 III classified as a red clump star — one actively burning helium in its core — at 172 ± 2 light-years. Zeta Piscis Austrini, an orange giant of spectral type K1 III at 413 ± 2 light-years, is listed as a suspected variable.