1. Origins

2. Characteristics

3. Features
    Stars  Deep sky objects 

4. Notes

5. References

6. External links

Piscis Austrinus is a constellation in the southern celestial hemisphere. The name is Latin for "the southern fish", in contrast with the larger constellation Pisces, which represents a pair of fishes. Prior to the 20th century, it was also known as Piscis Notius. Its only star brighter than 4th magnitude is Fomalhaut, which is a 1st-magnitude star and is the 18th-brightest star in the night sky.

Piscis Austrinus was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. The stars of the modern constellation Grus once formed the "tail" of Piscis Austrinus. In 1597 (or 1598), Petrus Plancius carved out a separate constellation and named it after the crane.

Origins

Pisces Austrinus originated with the Babylonian constellation simply known as the Fish (MUL.KU).^[1][2] Professor of astronomy Bradley Schaefer has proposed that ancient observers must have been able to see as far south as Mu Piscis Austrini to define a pattern that looked like an fish.^[3]

Piscis Austrinus, along with the eagle Aquila the crow Corvus and water snake Hydra, were introduced to the Greeks around 500 BCE; they marked the summer and winter solstices respectively.^[4]

In Greek mythology, this constellation is known as the Great Fish and it is portrayed as swallowing the water being poured out by Aquarius, the water-bearer constellation. The two fish of the constellation Pisces are said to be the offspring of the Great Fish. In Egyptian mythology, this fish saved the life of the Egyptian goddess Isis, so she placed this fish and its descendants into the heavens as constellations of stars.^[5] Ctesias wrote that the fish was said to have lived in a lake near Bambyce in Syria and had saved Derceto, daughter of Aphrodite, and for this deed was placed in the heavens. For this reason, fish were sacred and not eaten by many Syrians.^[6]

Characteristics

Piscis Austrinus is a constellation bordered by Capricornus to the northwest, Microscopium to the southwest, Grus to the south, Sculptor to the east, Aquarius to the north. Its recommended three-letter abbreviation, as adopted by the International Astronomical Union in 1922, is 'PsA'.^[7] Ptolemy called the constellation Ichthus Notios "Southern Fish" in his Almagest; this was Latinised to Piscis Notius and used by German celestial cartographers Johann Bayer, Johann Bayer, and Johann Elert Bode.^[8] Bayer also called it Piscis Meridanus and Piscis Austrinus, while French astronomer Nicolas-Louis de Lacaille called it Piscis Australis. English Astronomer Royal John Flamsteed went with Piscis Austrinus, which was followed by most subsequently.^[9] The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between {{RA|21|27.3}} and {{RA|23|06.5}}, while the declination coordinates are between -24.83° and -36.46°.^[9] The whole constellation is visible to observers south of latitude 53°N.^[10]{{efn|1=While parts of the constellation technically rise above the horizon to observers between 53°N and 65°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.^[10]}}

Features

Stars

Ancient astronomers counted 12 stars as belonging to the Southern Fish, though one was later incorporated into nearby Grus as Gamma Gruis.^[6] Other stars became part of Microscopium.^[8] Bayer used the Greek letters alpha through mu to label the most prominent stars in the constellation. Ptolemy had catalogued Fomalhaut (Alpha Piscis Austrini) as belonging to both this constellation and Aquarius. Lacaille redrew the constellation as it was poorly visible from Europe, adding nu, pi and a new kappa as the original kappa became Gamma Gruis, and relabelling gamma, delta and epsilon as epsilon, eta and gamma respectively. However, Baily and Gould did not uphold these changes as Bayer's original chart was fairly accurate. Bode added tau and upsilon. Flamsteed gave 24 stars Flamsteed designations, though the first four numbered became part of Microscopium.^[11] Within the constellation's borders, there are 47 stars brighter than or equal to apparent magnitude 6.5.{{efn|1=Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.^[12]}}^[10]

Traditionally representing the mouth of the fish, Fomalhaut is the brightest star in the constellation and the 1th brightest star in the night sky, with an apparent magnitude of 1.16. Located 25.13 ± 0.09 light-years away, it is a white main sequence star that is 1.92 ± 0.02 times as massive and 16.63±0.48 as luminous as the Sun.^[13] Its companion Fomalhaut b was thought to be the first extrasolar planet ever detected by a visible light image, thanks to the Hubble Space Telescope, but infrared observations have since retracted this claim: it is instead a spherical cloud of dust. TW Piscis Austrini can be seen close by and is possibly associated with Fomalhaut as it lies within a light-year of it. Of magnitude 6.5, it is a BY Draconis variable.^[14]

The second brightest star in the constellation,^[20] Epsilon Piscis Austrini is a blue-white star of magnitude +4.17. Located 400 ± 20 light-years distant,^[15] it is a blue-white main sequence star 4.10 ± 0.19 times as massive as the Sun, and around 661 times as luminous.

Lacaille 9352 is a faint red dwarf star which is a mere 10.74 light-years away. At magnitude 7.34, it is too dim to be seen with the naked eye.

Exoplanets have been discovered in five other star systems in the constellation. HD 205739 is a yellow-white main sequence star that has a Jupiter-like planet orbiting it. HD 216770 is an orange dwarf accompanied by one, possibly two, planets. HD 207832 is a sunlike star with two planets. WASP-112 and WASP-124 are two sunlike stars that have planets discovered by transit.

Deep sky objects

NGC 7172, NGC 7174 and NGC 7314 are three galaxies of magnitudes 11.9, 12.5 and 10.9, respectively.^[14] NGC 7259 is another spiral galaxy, which hosted a supernova—SN 2009ip—in 2009.

PKS 2155-304, a BL Lacertae object is one of the brightest blazars in the sky.

Notes

References

• Ian Ridpath and Wil Tirion (2017). Stars and Planets Guide, Collins, London. {{ISBN|978-0-00-823927-5}}. Princeton University Press, Princeton. {{ISBN|978-0-691-17788-5}}.

External links

• Warburg Institute Iconographic Database (over 150 medieval and early modern images of Piscis Austrinus - Piscis magnus)

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