Fomalhaut (Alpha Piscis Austrini): The Eye of Sauron Star

Fomalhaut, Alpha Piscis Austrini (α PsA), is a white main sequence star located in the constellation Piscis Austrinus, the Southern Fish. Shining at magnitude 1.16 from a distance of 25.13 light-years, it is the brightest star in Piscis Austrinus and the 18th brightest star in the sky. Along with two distant companions, Fomalhaut B and C, it forms one of the widest star systems known.

In 2008, astronomers announced the discovery of Fomalhaut b, the first candidate exoplanet ever photographed in visible light to be orbiting Fomalhaut. However, Fomalhaut b was likely never a planet. It was later revealed to be an expanding cloud of dust produced by a collision between two planetesimals in Fomalhaut’s large dust belt.

In 2023, Hubble caught a second cloud appearing in the same belt and, in 2025, a study showed how a dust cloud can masquerade as a planet for years. Fomalhaut’s belt itself, a vast ring of icy debris, has earned the star the nickname “the Eye of Sauron,” a reference to J.R.R. Tolkien’s mythos. It was imaged by the James Webb Space Telescope in 2023. The images revealed two inner belts that had never been seen before.

This image shows Fomalhaut, a star much hotter than our Sun, 16 times as bright, and located 25 light-years from Earth. It is blazing through hydrogen at such a furious rate that it will burn out in only one billion years, 10% the lifespan of our star. The field of view is 2.7 x 2.9 degrees. Image: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble) (CC BY 4.0)

Fomalhaut at a glance

A triple star system spanning over 7 degrees

Fomalhaut is part of a triple star system, but its companions are so far away that astronomers did not confirm them until 2012 and 2013. The Alpha Piscis Austrini system consists of Fomalhaut itself (Alpha Piscis Austrini A), the orange dwarf TW Piscis Austrini (Alpha Piscis Austrini B), and the red dwarf LP 876-10 (Alpha Piscis Austrini C). The fainter components are commonly referred to as Fomalhaut B and Fomalhaut C.

The astronomer Willem Luyten first suggested in 1938 that TW Piscis Austrini was a physical companion to Fomalhaut based on its similar motion and distance. It was only in 2012 that a study showed they are very likely bound. LP 876-10 officially joined the family as Fomalhaut C in 2013.

With an apparent magnitude of 6.44 – 6.51, TW Piscis Austrini is right at the limit of unaided eye visibility, while LP 876-10 is a target for small telescopes, shining at magnitude 12.624.

The Fomalhaut system is one of the widest star systems known. The faintest component, Fomalhaut C, does not even appear in the same constellation as the other two. It lies across the border in Aquarius. Fomalhaut and Fomalhaut B are separated by more than 2 degrees (four full Moons), and Fomalhaut and Fomalhaut C by 5.7 degrees. The separation between Fomalhaut B and Fomalhaut C is well over 7 degrees (14 full Moons).

In three-dimensional space, that means around 0.9 light-years between Fomalhaut and TW Piscis Austrini and 2.5 light-years between Fomalhaut and LP 876-10. TW Piscis Austrini is estimated to need roughly 5.8 million years to circle Fomalhaut, and LP 876-10 about 20 million years. However, both figures are uncertain. For comparison, Proxima Centauri lies only around 0.2 light-years (2.18°) from Alpha Centauri A and B and takes around 550,000 years to orbit the bright pair.

Astronomers have suggested that Fomalhaut and LP 876-10 formed together and that the system later captured TW Piscis Austrini from their birth cluster. LP 876-10 hosts a debris disk of its own, which is unusual for a red dwarf, and TW Piscis Austrini is the only one without a disk. The red dwarf’s disk may be explained by a past encounter with Fomalhaut.

The Fomalhaut star system, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

Fomalhaut (Alpha Piscis Austrini A)

Fomalhaut has the stellar classification A4 V, indicating a hydrogen-fusing dwarf, appearing white or blue-white in colour. The star has almost twice the Sun’s mass (1.92 M_☉) and radius (1.842 R_☉). With an estimated surface temperature of 8,590 K, it shines with 16.63 solar luminosities.

A 2012 study of the star’s age and binarity gave an estimated age of 440 million years. The same study unequivocally confirmed that TW Piscis Austrini was a physical companion to Fomalhaut, with a similar velocity and at a separation of 0.280 parsecs (0.91 light-yeas) from the primary.

Even though Fomalhaut is much younger than the Sun (4.5 billion years), as the more massive star, it has evolved faster. It will exhaust the supply of hydrogen in its core within a billion years and evolve into a red giant before expelling its outer layers to form a planetary nebula and gradually fading away as a white dwarf.

The large disk surrounding Fomalhaut is clearly visible in this image. It is not centred on Fomalhaut quite as predicted, hinting that the gravity of another body – perhaps a planet – is pulling it out of shape. Image credit: NASA, ESA and P. Kalas (University of California, Berkeley, USA) (PD)

Fomalhaut compared to Vega

Fomalhaut belongs to a small group of A-type main sequence stars near the Sun that shine at first magnitude. The other three are Sirius, Vega, and Altair. Sirius outshines all of them by a wide margin. Altair appears brighter than Fomalhaut simply because it is closer, even though Fomalhaut is the more luminous of the two.

Vega is the more telling comparison. It lies at almost the same distance as Fomalhaut and appears over a full magnitude brighter because it is hotter, more massive and more luminous.

Fomalhaut is considered to be a Vega-like star. Like Vega, it emits excess infrared radiation that indicates the presence of a circumstellar debris disk. Both stars have disks of dust replenished by collisions among asteroids, comets and planetesimals. However, Vega’s disk is much smoother, without major gaps or other signs of large planets shaping the dust.

Fomalhaut and Vega were once thought to be relatives. Both were assigned to the disputed Castor moving group, a proposed stellar association that also included Castor. However, the members were later found to have different ages and velocities, indicating that they are not associated with one another.

This view shows a picture of the dust ring around the bright star Fomalhaut from the Atacama Large Millimeter/submillimeter Array (ALMA). The underlying blue picture shows an earlier picture obtained by the NASA/ESA Hubble Space Telescope. The new ALMA image has given astronomers a major breakthrough in understanding a nearby planetary system and provided valuable clues about how such systems form and evolve. Note that ALMA has so far only observed a part of the ring. Image credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope. Acknowledgement: A.C. Boley (University of Florida, Sagan Fellow), M.J. Payne, E.B. Ford, M. Shabran (University of Florida), S. Corder (North American ALMA Science Center, National Radio Astronomy Observatory), and W. Dent (ALMA, Chile), P. Kalas, J. Graham, E. Chiang, E. Kite (University of California, Berkeley), M. Clampin (NASA Goddard Space Flight Center), M. Fitzgerald (Lawrence Livermore National Laboratory), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion Laboratory) (CC BY 4.0)

How bright is Fomalhaut compared to other stars?

With an apparent magnitude of 1.16, Fomalhaut is the 18th brightest star in the night sky. It is about 11 times fainter than Sirius and roughly twice as bright as Polaris.

Among its nearest rivals in brightness, Fomalhaut is fainter than Spica in Virgo, which shines at magnitude 0.97, and usually fainter than Antares in Scorpius, whose brightness varies from magnitude 0.6 to 1.6. Pollux in Gemini is slightly brighter at magnitude 1.14, but the difference is imperceptible to the unaided eye so the two appear equally bright.

Fomalhaut is brighter than Deneb in Cygnus and Mimosa in Crux, both listed near magnitude 1.25, and Regulus in Leo at about magnitude 1.40.

This ranking is primarily a consequence of distance. Fomalhaut has a luminosity of 16.63 Suns, but it lies relatively close to us. With the exception of Sirius (8.61 ly, 24.74 L_☉) and Pollux (33.78 ly, 38.4 L_☉), all the abovementioned stars lie much further away and are much more intrinsically luminous.

A role in celestial navigation

Fomalhaut is one of the 58 stars selected for use in navigation. Navigational stars have a special role in the field of celestial navigation because they are some of the brightest and most identifiable stars in the night sky.

Fomalhaut is the only navigational star in its faint home constellation. The other navigational stars in the same region of the sky include Ankaa (Alpha Phoenicis), Diphda (Beta Ceti), and Alnair (Alpha Gruis), the brightest stars in Phoenix, Cetus, and Grus.

Fomalhaut B (TW Piscis Austrini)

TW Piscis Austrini is an orange main sequence star of the spectral type K5Vp. It lies 0.91 light-years (0.28 parsecs) from Fomalhaut. Both its velocity and estimated age indicate that the two stars are physically related.

Compared with Fomalhaut, TW Piscis Austrini is a modest star. It has an estimated mass of 0.73 solar masses and a radius 68.8% that of the Sun. Its estimated surface temperature is 4,594 K and its luminosity only 0.189 L_☉. The star spins at 2.93 km/s, taking 10.3 days to complete a rotation.

The rotation period plays a role in the star’s brightness variations. TW Piscis Austrini is classified as a BY Draconis variable, a star whose brightness changes as dark starspots rotate in and out of view. The star’s light varies only slightly, by about 0.05 magnitudes (6.44 to 6.49) over those 10.3 days.

Fomalhaut B is also a flare star, showing sudden dramatic increases in brightness for very short periods (minutes). While it is smaller and less massive than the Sun, it is significantly larger than most flare stars, which are typically small red dwarfs.

In 2019, a team led by Robert J. De Rosa reported a possible astrometric signature of an orbiting planet around Fomalhaut B. By comparing measurements from the Hipparcos and Gaia missions, the researchers found an apparent acceleration in the star’s motion across the sky, one that could not be explained by the star’s wide orbit around Fomalhaut.

While the team did not establish the presence of a planet with any degree of certainty, a planetary companion of about 1.2 Jupiter masses with an orbital period of about 25 years may account for the acceleration. If it is real, the planet could be a promising target for direct imaging with the James Webb Space Telescope or the Nancy Grace Roman Space Telescope.

Fomalhaut and TW Piscis Austrini, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

Fomalhaut C (LP 876-10)

The red dwarf LP 876-10 has the spectral type M4V and a surface temperature of 3,132 K. It lies in the neighbouring constellation Aquarius, about 5.7 degrees (over 11 full Moons) from Fomalhaut. In the sky, the faint star appears roughly halfway between Fomalhaut and the Helix Nebula. The physical separation between Fomalhaut C and Fomalhaut is 2.5 light years and between Fomalhaut C and TW Piscis Austrini it is 3.2 light-years.

LP 876-10 has a mass of 0.18 solar masses and shines with only 0.0046 solar luminosities. With an apparent magnitude of 12.624, it is well below unaided eye visibility. The star has a radius only 23% that of the Sun.

The red dwarf takes 20 million years to orbit Fomalhaut. With an estimated age of 440 million years for the star system, Fomalhaut C would have completed only 22 full orbits around the primary component.

The red dwarf was confirmed to be a member of the Alpha Piscis Austrini system in October 2013, when Eric Mamajek of the University of Rochester announced that the star’s velocity, distance and colour-magnitude position indicated that it was part of the Fomalhaut system.

In 2013, infrared observations with the Herschel Space Observatory revealed a cold debris disk around the star. The disk has an estimated temperature of only 24 K and orbits at a distance between 10 and 40 astronomical units from the star. Like the disk around Fomalhaut A, it is believed to host planetesimals and comet-like bodies. The disk was imaged by the Atacama Large Millimeter/submillimeter Array (ALMA) in 2021 and the James Webb Space Telescope in 2024.

Fomalhaut, Fomalhaut C and the Helix Nebula, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)

The Eye of Sauron: Fomalhaut’s debris belts

Fomalhaut is surrounded by several large debris disks. The dust in the disks is produced by collisions between comets and asteroids, and it forms debris structures and belts similar to the Sun’s asteroid and Kuiper belts. In 1983, NASA’s Infrared Astronomical Satellite (IRAS) detected the first sign of the largest one, an excess of infrared light coming from the star.

The innermost disk lies 0.1 astronomical units from the star. It is a ring of tiny, carbon-rich dust grains, each only about 10-300 nanometres wide. The middle disk stretches from 0.4 to 1 AU from the star and contains larger particles.

The inner edge of the largest, outermost disk lies around 133 AU from the star, along the plane of the star’s equator, and contains a belt of dust around 25 AU wide. Sometimes called Fomalhaut’s Kuiper Belt, it is the ring behind the “Eye of Sauron” nickname. It stretches out to 23 billion kilometres from Fomalhaut. This is 150 times the distance from Earth to the Sun.

The outer ring has been imaged by Hubble, Herschel, and ALMA. Hubble images showed the first signs that the gravity of unseen planets is sculpting it. Herschel detected fluffy dust grains, indicating constant collisions that replenish the belt’s dust. Astronomers estimated an approximate rate of 2,000 collisions per day between one-kilometre-sized comets needed to sustain the vast dust ring around the star.

This image from the Atacama Large Millimeter/submillimeter Array (ALMA) shows Fomalhaut (centre) encircled by a ring of dusty debris — this is the first time this scene has been captured at such high resolution and sensitivity at millimetre wavelengths. Fomalhaut’s disc comprises a mix of cosmic dust and gas from comets in the Fomalhaut system (exocomets), released as the exocomets graze past and smash into one another. This turbulent environment resembles an early period in our own Solar System, which occurred approximately four billions years ago. This era saw huge numbers of rocky objects hurtle into the inner Solar System and collide with the young terrestrial planets, including Earth, where they formed a myriad of impact craters — many of which remain visible today on the surfaces of planets such as Mercury and Mars. Image credit: ALMA (ESO/NAOJ/NRAO)/L. Matrà/M. A. MacGregor (CC BY 4.0)

A bird’s-eye comparison of the Fomalhaut ring with our solar system. In this graphic, Fomalhaut’s ring, about 25 billion miles (about 40 billion kilometres) across its inner diameter, is compared with our inner and outer solar system. Image credit: NASA, ESA and A. Feild (STScI) (CC BY 4.0)

Webb finds three nested belts

In 2023, astronomers used the James Webb Space Telescope (JWST) to capture Fomalhaut’s debris ring. Webb’s Mid-Infrared Instrument (MIRI) revealed a more complex dust structure than previously thought and provided scientists with new insights into the first asteroid belt detected outside the solar system.

The Webb image showed three nested belts and resolved the two inner belts for the first time. The middle belt was found to be misaligned with the outer ring and have an inner gap at about 78 AU. Webb also spotted a large dust cloud in the outermost belt, which astronomers named “the Great Dust Cloud.” It is thought to be a cloud of fine dust produced in a collision between two larger bodies.

This image of the dusty debris disc surrounding the young star Fomalhaut is from Webb’s Mid-Infrared Instrument (MIRI). It reveals three nested belts extending out to 23 billion kilometres from the star. The inner belts — which had never been seen before — were revealed by Webb for the first time. Image credit: NASA, ESA, CSA, A. Pagan (STScI), A. Gáspár (University of Arizona) (CC BY 4.0)

Where are the planets?

All three belts appear to be affected by planetary-mass objects, much like Neptune shapes the inner edge of the Kuiper Belt. However, no planets have been confirmed in the Fomalhaut system to date. The patterns in the rings will help astronomers understand what a planetary system around Fomalhaut may look like.

The study of Fomalhaut’s debris disks, led by András Gáspár of the University of Arizona in Tucson, was published in the journal Nature Astronomy.

Hubble observations show that the bright star Fomalhaut is off-center from its surrounding ring of dust, most likely because of a planet orbiting the star and shepherding the ring material. Image credit: NASA, ESA and A. Feild (STScI) (CC BY 4.0)

Fomalhaut b: The planet that wasn’t

Fomalhaut was believed to host an extrasolar planet, Fomalhaut b, for years before the planet was revealed to likely be a dust cloud in Fomalhaut’s outer debris ring. The phantom planet was discovered in 2008, disputed in 2011, re-discovered in 2012, and ultimately removed from the list of exoplanet candidates in the NASA Exoplanet Archive in 2020. Infrared observations with the James Webb Space Telescope in 2023 supported the interpretation that Fomalhaut b was, in fact, a dust cloud.

The first “planet” seen in visible light

The discovery of Fomalhaut b was announced on November 13, 2008. The candidate planet was imaged by the Hubble Space Telescope and would have been the first extrasolar planet to be captured in visible light. The presence of a planet had already been suspected because the sharp inner edge of Fomalhaut’s debris belt looked sculpted by one. Fomalhaut b was reported to orbit just inside that edge.

The Hubble images released in 2008 revealed a planet-like object close to Jupiter in mass (between 0.2 and 2 Jovian masses) and were consistent with the earlier predictions of a planet orbiting at a distance of 119 astronomical units, taking 872 years to complete an orbit around Fomalhaut.

This labeled visible-light image from the Hubble Space Telescope combines two 2006 observations and shows the Fomalhaut system. It includes the locations of its dust ring and Fomalhaut b, a proposed exoplanet that orbits the star. A coronagraphic mask was used to help dim Fomalhaut. Image credit: NASA/ESA/T. Curie/U. Toronto (CC BY 4.0)

“Zombie planet”

Fomalhaut b never behaved like a planet should. It shone in visible light but disappeared in the infrared, where a giant planet should have glowed. In 2012, Spitzer did not detect it, leading astronomers to propose that the source was scattered light from a dust cloud and not a planet.

Two studies in 2012 and 2013 pushed back, concluding that Fomalhaut b was a real planet shrouded in dust. Since the object had been written off and revived, it earned the nickname “zombie planet.”

In 2015, the International Astronomical Union (IAU) gave Fomalhaut b the proper name Dagon, after the Bronze Age Canaanite deity associated with fertility and depicted as half-man, half-fish. At the time, the object was still considered to be a planet candidate.

Two dust-cloud impostors

A 2020 study led by András Gáspár of the University of Arizona found that the candidate planet is fading and that it grew in size since its discovery. The team analyzed data obtained with the Space Telescope Imaging Spectrograph (STIS) aboard Hubble and concluded that Fomalhaut b is an expanding dust cloud. The large amounts of dust detected by Hubble were likely produced in a massive planetesimal collision, the first one seen in an exoplanetary system.

In 2023, Hubble detected another dust cloud at the inner edge of Fomalhaut’s belt, that did not appear in previous images. The 2025 study in Science reported that Fomalhaut b, now called Fomalhaut cs1, and the new source, Fomalhaut cs2, looked like the same phenomenon, two dust clouds produced in collisions between massive objects.

Even though Fomalhaut b turned out not to be a planet, this does not mean that Fomalhaut does not host any planets. The sculpted belts imaged by ALMA and James Webb hint at the presence of planets, but none has been found to date.

Observations with the James Webb Space Telescope in 2023 led to the detection of ten sources in Fomalhaut’s dusty disks. One of these sources, located at the edge of the inner dust disk, may be an orbiting planet. However, further observations are necessary to confirm its true nature. It may be a brown dwarf or possibly a background galaxy instead.

Expansion of the dust cloud formerly designated Fomalhaut b, image: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona) (PD)

This composite NASA/ESA Hubble Space Telescope image shows the debris ring and dust clouds cs1 and cs2 around the star Fomalhaut. For comparison, dust cloud cs1, imaged in 2012, is pictured with dust cloud cs2, imaged in 2023. The dashed circles mark the location of these clouds. When dust cloud cs2 suddenly appeared, astronomers quickly noticed they had witnessed the violent collision of two massive objects. Previously thought to be a planet, cs1 is now classified as a similar debris cloud. In this image, Fomalhaut itself is masked out to allow the fainter features to be seen. Its location is marked by the white star. Image credit: NASA, ESA, P. Kalas (UC Berkeley), J. DePasquale (STScI) (CC BY 4.0)

The meaning of the name Fomalhaut

The name Fomalhaut (pronunciation: /ˈfoʊməl.hɔːt/) comes from the Arabic phrase fam al-ḥūt (al-janūbī), meaning “the mouth of the (southern) fish.”

The International Astronomical Union’s (IAU) Working Group on Star Names (WGSN) officially approved the name for Alpha Piscis Austrini A on December 15, 2015.

Association with Aquarius

In traditional images of this part of the sky, Aquarius is seen pouring a stream of water into the mouth of the Southern Fish. Fomalhaut marks the fish’s mouth, linking the two constellations in a larger “celestial sea” of water-associated constellations.

In historical star atlases, Fomalhaut was catalogued under both Piscis Austrinus and Aquarius. The Greco-Roman astronomer Ptolemy associated the star with both constellations in the 2nd century CE.

The German uranographer Johann Bayer gave it the designation Alpha Piscis Austrini, placing it definitively in Piscis Austrinus as the constellation’s brightest star in his Uranometria (1603).

The English astronomer John Flamsteed designated the star 24 Piscis Australis in his Historia Coelestis Britannica (1725) and assigned it the additional designation 79 Aquarii. Today, Fomalhaut belongs only to Piscis Austrinus.

Aquarius and Piscis Austrinus (Piscis Meridionalis), The Mercator Globes at Harvard Map Collection, 1551

Fomalhaut in culture

Fomalhaut has been known by many other names across different cultures. The Latin names for the star included Os Piscis Meridiani, Os Piscis Meridionalis and Os Piscis Notii.

The Persians called the star Hastorang in 2582 BCE and considered it one of the four “royal stars.” The royal stars of Persia – Fomalhaut in Piscis Austrinus, Aldebaran in Taurus, Regulus in Leo, and Antares in Scorpius – were regarded as the guardians of heaven.

Fomalhaut’s other Arabic name was Difda al Auwel, derived from aḍ–ḍifdiˤ al-’awwal, meaning “the first frog.” The second frog was the nearby Diphda (Beta Ceti).

The Moporr people of Victoria, Australia know Fomalhaut as Buunjill (the name refers to a masculine being), and the Wardaman people of the Northern Territory call it Menggen, meaning “white cockatoo.”

In traditional Chinese astronomy, Fomalhaut is known as 北落師門/北落师门 (Běiluòshīmén), the North Gate of the Military Camp. The star is the sole member of the North Gate asterism, which is part of the larger Encampment mansion, one of the northern mansions of the Black Tortoise.

Fomalhaut in fiction

Like many other bright and nearby stars, Fomalhaut has been used in countless works of fiction. Notable uses and mentions include the novel Pebble in the Sky (1950) by Isaac Asimov, Gordon R. Dickson’s Dorsai! (1960), Stanislaw Lem’s Return from the Stars (1961), Jack Vance’s Star King (1964), Ursula K. Le Guin’s Rocannon’s World (1966), Philip K. Dick’s The Unteleported Man (1966), The Divine Invasion (1981) and Radio Free Albemuth (1985), The Zero Stone (1968) by Andre Norton, Joe Haldeman’s The Forever War (1974), Richard Avery’s The War Games of Zelos (1975), Frank Herbert’s Children of Dune (1976), Greg Egan’s Diaspora (1997), and Paul J. McAuley’s In the Mouth of the Whale (2012).

The lonely star of autumn: How to find Fomalhaut

Fomalhaut lies in the southern celestial hemisphere, in a faint region of the sky without any distinctive features. The constellation Piscis Austrinus does not stand out in the sky and is surrounded by the faint Aquarius, Capricornus, Microscopium, Sculptor, and the slightly brighter Grus.

The easiest way to identify Fomalhaut is using the bright stars of the Great Square of Pegasus. A line drawn through the western side of the asterism, from Scheat through Markab, points in the general direction of the star. Even though Markab and Fomalhaut are separated by about 45 degrees, there are no other bright stars in the area between.

At declination -30°, Fomalhaut never rises for observers north of the latitude 60° N. It is largely invisible from Alaska, northern Canada and Russia, Greenland, Iceland, and the Scandinavian countries.

Location of Fomalhaut, image: Stellarium (annotated for this article)

Seen from the southern hemisphere, Fomalhaut lies roughly along an imaginary line drawn from Canopus, the second brightest star in the sky, through Achernar, the ninth brightest star. Fomalhaut forms a large, almost equilateral triangle with Achernar and the fainter Peacock in Pavo, and a smaller triangle with the fainter Alnair in Grus and Ankaa in Phoenix.

Fomalhaut in the southern hemisphere, image: Stellarium (annotated)

Fomalhaut and the Helix Nebula

Fomalhaut can be used to find the famous Helix Nebula (NGC 7293), one of the brightest planetary nebulae in the sky. Like Fomalhaut, the nebula has been nicknamed the “Eye of Sauron” (or the “Eye of God”) because it appears like a giant eye in the sky. It lies about 10 degrees northwest of the star, roughly halfway from Fomalhaut to Iota Aquarii, a magnitude 4.3 star that appears east-northeast of Deneb Algedi, the brightest star in Capricornus. The Helix Nebula can be seen in small telescopes in good conditions.

Fomalhaut’s home constellation: Piscis Austrinus

Fomalhaut is the brightest star of Piscis Austrinus (the Southern Fish), a small constellation in the southern sky that does not contain any other stars brighter than magnitude 4.0. The star marks the mouth of the fish.

Piscis Austrinus occupies an area of 245 square degrees and is the 60th largest of the 88 constellations. It was one of the 48 Greek constellations catalogued by Claudius Ptolemy of Alexandria in his Almagest in the 2nd century CE.

Once also known as Piscis Notius, Piscis Austrinus represents the Southern Fish, or the Great Fish in Greek mythology. The association with the fish originated in the Babylonian constellation MUL.KU (the Fish). Piscis Austrinus is usually depicted as swallowing the water poured by the neighbouring Aquarius, the Water Bearer. The two fish represented by the zodiac constellation Pisces are said to be the offspring of the Greek Great Fish.

The brightest stars in Piscis Austrinus include the hot blue main sequence star Epsilon Piscis Austrini, the yellow giant Delta Piscis Austrini, the A-type stars Tiangang (Beta Piscis Austrini), Baijiu (Iota Piscis Austrini), Gamma Piscis Austrini, and Mu Piscis Austrini, the F-type main sequence star Tau Piscis Austrini, and the orange giant Upsilon Piscis Austrini. These are the only stars in the constellation that are brighter than magnitude 5.0.

Piscis Austrinus does not contain many bright deep sky objects. It is home to the galaxies NGC 7172, NGC 7174, NGC 7214, NGC 7314, and NGC 7259, the last of which hosted a supernova observed in 2009 and designated SN 2009ip. The spiral galaxies NGC 7172 and NGC 7174 form the Hickson Compact Group 90 (HCG 90) with the elliptical galaxies NGC 7173 and NGC 7176.

Piscis Austrinus constellation map by IAU and Sky&Telescope magazine (Roger Sinnott & Rick Fienberg) (CC BY 3.0)

The best time of the year to observe Fomalhaut and other stars of Piscis Austrinus is in October, when the constellation appears higher above the horizon in the evening sky. The entire constellation is visible from locations south of the latitude 55° N.

The 10 brightest stars in Piscis Austrinus are Fomalhaut (Alpha PsA, mag. 1.16), Epsilon Piscis Austrini (mag. 4.17), Delta Piscis Austrini (mag. 4.175), Tiangang (Beta PsA, mag. 4.29), Baijiu (Iota PsA, mag 4.35), Gamma Piscis Austrini (mag. 4.448), Mu Piscis Austrini (mag. 4.49), Tau Piscis Austrini (mag. 4.945), Upsilon Piscis Austrini (mag. 4.98), and Theta Piscis Austrini (mag. 5.01).

Alpha Piscis Austrini

Fomalhaut – Alpha Piscis Austrini A              

Fomalhaut B – TW Piscis Austrini          

Fomalhaut C – LP 876-10