The Piscis Austrinus Constellation

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. 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, Petrus Plancius carved out a separate constellation and named it after the crane. 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. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 21h 27.3m and 23h 06.5m, while the declination coordinates are between -24.83° and -36.46°. The whole constellation is visible to observers south of latitude 53°N.

Within the constellation’s borders, there are 47 stars brighter than or equal to apparent magnitude 6.5. Fomalhaut, Alpha Piscis Austrini, is the brightest star in the constellation. With an apparent magnitude of 1.16, it is also the 18th brightest individual star in the night sky. It is a white main sequence star with the stellar classification of A3 V, approximately 25.13 light years from Earth. Fomalhaut has 1.92 times the Sun’s mass and 1.842 times the solar radius. It is 16.63 times more luminous than the Sun. The star emits excess infrared radiation, which suggests that it has a circumstellar disk in its orbit. Fomalhaut is in fact surrounded by several debris disks. Fomalhaut traditionally represents the mouth of fish. 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. Fomalhaut belongs to the Castor Moving Group, a stellar association that also includes the bright stars Castor in Gemini and Vega in Lyra constellation. The stars in the group share a common motion through space and same location of origin, and they might be physically associated. NGC 7172 is a spiral galaxy with an apparent magnitude of 11.9.

NGC 7172, NGC 7174 and NGC 7314 are three galaxies of magnitudes 11.9, 12.5 and 10.9, respectively. NGC 7172 is a spiral galaxy, classified as a Seyfert 2 galaxy. NGC 7174 and NGC 7314 are also spiral galaxies. NGC 7173 is an elliptical galaxy in Piscis Austrinus constellation. It has an apparent magnitude of 11.9 and is about 114.8 million light years distant from the solar system. It was discovered by the English astronomer John Herschel on September 25, 1834. Together with NGC 7174 and NGC 7176, it is one of the three interacting galaxies in the Hickson Compact Group 90. The three galaxies will eventually merge into one. HCG 90 is approximately 100 million light years distant from Earth.

PKS 2155-304, a BL Lacertae object is one of the brightest blazars in the sky. Credits: Constellation Guide, Wikipedia.