IAU Constellation (PsA) · Genitive: Piscis Austrini · Southern Sky

Piscis Austrinus & Fomalhaut Sky Guide

Piscis Austrinus IAU constellation (245 sq deg, rank 60): October autumn constellation south of Aquarius anchored by first-magnitude Fomalhaut (+1.16).

Solid-Angle Area245 sq deg (Rank #60 of 88)
Best Evening MonthOctober
Visibility Latitudes+55° to −90°
Brightest StarFomalhaut (Alpha Piscis Austrini) (+1.16)

Sky Navigation & Astrophysical Context

Covering 245 square degrees south of Aquarius, Piscis Austrinus is one of the oldest constellations in human astronomy, originating in Babylonian star lore as MUL.KU ('The Fish') that swallows the stream of water poured from the jar of Aquarius. In Greco-Roman myth, this 'Great Fish' is the parent of the two smaller fishes of zodiacal Pisces.

The constellation is overwhelmingly dominated by its mouth star, Fomalhaut (Alpha Piscis Austrini, from the Arabic 'Fam al-Hut al-Janubi,' V = +1.16), the eighteenth-brightest star in the sky. Because Fomalhaut shines in a famously sparse autumn region ('The Solitary One of the Autumn Sky'), it served in ancient Persia as one of the four 'Royal Stars' guarding the winter solstice alongside Aldebaran, Regulus, and Antares.

Astrophysically, Fomalhaut is a young (~440-million-year-old) A3 V main-sequence star at just 7.70 parsecs (25.1 light-years) that forms a wide physical triple system extending over 5° of the sky with the K4 V orange flare star TW Piscis Austrini (+6.48, 0.28 parsecs away) and the M4 V red dwarf LP 876-10 (Fomalhaut C). Fomalhaut A is encircled by a famous, eccentric 133-AU icy Kuiper-belt analog debris ring resolved in stunning detail by HST, ALMA, and JWST, while southern Piscis Austrinus also contains Lacaille 9352, the fourth-closest red dwarf to Earth at 3.29 parsecs.

Bordering IAU Constellations: Aquarius, Capricornus, Microscopium, Grus, Sculptor.

Equatorial Center Position & Transit Altitude

Piscis Austrinus is centered near Right Ascension 22h 16m 48s, Declination −30° 38′ 24″ (The Southern Fish).

J2000 Equatorial Sky Position (Piscis Austrinus) +90° 0° −90° 24h 12h RA 0h Peak Meridian Altitude 19° 40°N Lat 89° 30°S Lat RA: 22h 16m 48s Dec: −30° 38′ 24″ Epoch: J2000.0 · 245 sq deg (Rank #60) First-party vector diagram derived from IAU / CDS SIMBAD / Gaia DR3 astrometry.

Practical Star-Hopping & Observing Tips

  • Extend a pointer line southward through the western stars of the Great Square of Pegasus (Scheat and Markab) 45° south across Aquarius to land directly on brilliant blue-white Fomalhaut (+1.16).
  • Look 1.9° southeast of Fomalhaut in binoculars to spot magnitude +6.48 TW Piscis Austrini (Fomalhaut B)—a physical K-dwarf companion sharing Fomalhaut's space motion at 25 light-years.
  • Split Beta Piscis Austrini (+4.29 A1 V primary and +7.8 companion separated by 30.3 arcseconds) in any small telescope.

Notable Celestial Objects in & Near Piscis Austrinus

Cataloged Stars and Deep-Sky Objects Associated with Piscis Austrinus
ObjectFamilyClassificationRA (J2000)Dec (J2000)Min. Instrument
Helix Nebula (NGC 7293 in Aquarius)nebulaeLarge evolved planetary nebula (nearest bright planetary nebula)22h 29m 38.55s-20° 50′ 13.8″10×50 binoculars under dark skies; wide-field telescope + O-III filter
TRAPPIST-1 e (Temperate Terrestrial World)exoplanetsTemperate terrestrial exoplanet in a 7-planet resonant chain23h 06m 29.28s-05° 02′ 28.6″250–350 mm telescope + near-IR/CMOS camera (V = 18.80, J = 11.35)
Fomalhaut (Alpha Piscis Austrini Debris Disk)starsYoung A-type main-sequence star with multi-belt debris disk (wide triple system)22h 57m 39.05s-29° 37′ 20.0″Naked eye (binoculars for companion Fomalhaut B)

Scientific Sources Cited