Constellations of the Month: October – Piscis Austrinus:
We continue October with the next constellation of the month, Piscis Austrinus, “The Southern Fish.”

Piscis Austrinus constellation map courtesy of Openverse

Piscis Austrinus, “The Southern Fish” – The Piscis Austrinus minor constellation is located in the southern hemisphere, and symbolizes “the southern fish.”  Piscis Austrinus is occasionally referred to as Piscis Australis. It was initially catalogued by the Greek astronomer Ptolemy during the 2^nd century, although its origins trace back to Babylonian times. Up until the 20^th century, the constellation was known as Piscis Notius. In the late 16^th century, the Dutch astronomer Petrus Plancius distinguished some of its stars to create a new constellation, Grus. Piscis Austrinus is considered a relatively small and dim constellation, featuring only one star that exceeds fourth magnitude in brightness and lacking many significant deep sky objects. The most luminous star within this constellation, Fomalhaut, is also among the brightest stars visible in the night sky, ranking at number 18 in brightness.

Arp 14 / NGC 7314 courtesy of Openverse

Key points regarding Piscis Austrinus:

• Meaning: The term “Piscis Austrinus” translates to “The Southern Fish” in Latin. Piscis Austrinus comprises six stars that have confirmed planets, and it lacks any Messier objects. The most luminous star in this constellation is Fomalhaut, designated as Alpha Piscis Austrini, which has an apparent magnitude of 1.16. Additionally, there are no meteor showers linked to this constellation. Within Piscis Austrinus, there are two stars that have been formally named. The names recognized by the International Astronomical Union (IAU) are Fomalhaut (Alpha Piscis Austrini A) and Sāmaya (HD 205739).
• Notable stars: Fomalhaut, or Alpha Piscis Austrini, is the brightest star in its constellation and the 18th brightest in the night sky. It is a white main sequence star located about 25.13 light years from Earth, with a mass 1.92 times that of the Sun. Fomalhaut emits excess infrared radiation, suggesting it has debris disks. It has historical significance and has been classified by several astronomers over time. TW Piscis Austrini, its companion star, is an orange dwarf located close by. Other notable stars in the constellation include Epsilon, Delta, Beta, Iota, and Gamma Piscis Austrini, each with unique characteristics and distances from Earth. Mu Piscis Austrini is a white A2V star, 130 light years away. Tau Piscis Austrini is a yellow-white F6V dwarf, 61 light years away and about 1.3 billion years old. Theta is a multiple star system, 339 light years distant. Pi is a binary star, 93 light years away. Eta is a multiple star system, 1,012 light years distant. Lacaille 9352 is a red dwarf, 10.68 light years away. HD 216770, an orange K1V dwarf, has a planet and is 123.5 light years away. S Piscis Austrini is a red giant variable star, while V Piscis Austrini is a semi-regular variable.
• Other features: Hickson Compact Group 90 (HCG 90) is about 100 million light years away and includes three galaxies: NGC 7173, NGC 7174, and NGC 7176. These galaxies are interacting and will eventually merge into one large elliptical galaxy. NGC 7173 is an elliptical galaxy with a magnitude of 11.9, discovered by John Herschel on September 25, 1834, and is 114.8 million light years away. NGC 7174 is a spiral galaxy with a magnitude of 12.5, found by Herschel on September 28, 1834. NGC 7176 is also an elliptical galaxy, with a magnitude of 11.5, discovered first by Herschel on September 23, 1834, and is about 115.5 million light years away. NGC 7314 is a Seyfert spiral galaxy with a magnitude of 11.9, visible in small telescopes. NGC 7172 is another spiral galaxy with a magnitude of 11.9 and is classified as a Seyfert 2 galaxy.
• Mythology: Piscis Austrinus is one of the 48 Greek constellations listed by the astronomer Ptolemy in the 2nd century CE. Originally, it included stars that are now part of the Grus constellation. Its roots trace back to Babylonian culture, where it was called the Fish, or MUL. KU, linked to the fertility goddess Atargatis. She fell into a lake and was saved by a fish, punishing those who ate fish, except for her priests. In another version, Atargatis threw herself into the lake and was transformed into a mermaid after abandoning her daughter, who was raised to become Semiramis, the Assyrian queen. The Greeks depicted it as the Great Fish that swallowed water poured by Aquarius. Similarly, in Greek mythology, Aphrodite turned into a fish and was saved by two fish in the Euphrates, which were later honored with the constellation Pisces. Egyptians also associated a fish with saving the goddess Isis, placing it in the sky.
• Visibility: Piscis Austrinus is the 60^th largest constellation, covering 245 square degrees. It is situated in the fourth quadrant of the southern hemisphere (SQ4) and is observable at latitudes ranging from +55° to -90°. The constellations that border it include Aquarius, Capricornus, Grus, Microscopium, and Sculptor. The name Piscis Austrinus is pronounced /ˈpaɪsɪs ɔːˈstraɪnəs/. In English, this constellation is referred to as the Southern Fish. The genitive form of Piscis Austrinus, which is utilized in the naming of stars, is Piscis Austrini (pronunciation: /ˈpaɪsɪs ɔːˈstraɪnaɪ/). The three-letter abbreviation, which was established by the International Astronomical Union (IAU) in 1922, is PsA. Piscis Austrinus is part of the Heavenly Waters family of constellations, which also includes Carina, Columba, Delphinus, Equuleus, Eridanus, Puppis, Pyxis, and Vela.

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Constellations:

Piscis austrinus courtesy of Openverse

Constellations of the Month:
October – Piscis Austrinus

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