Piscis Austrinus

Piscis Austrinus in the Sky

From ancient times the region of the sky southward of Aquarius and Capricornus has been known as the 'Fish', though it is now more fully named Piscis Austrinus (or sometimes Piscis Australis), the 'Southern Fish', to distinguish it from Pisces on the Ecliptic, which lies northward of Piscis Austrinus beyond Aquarius.

The constellation's original form was rather more extensive than it is today, with a long tail running southward from the fish's main body. That 'tail' now forms the separate constellation of Grus, the Crane, leaving Piscis Austrinus as a relatively small constellation representing the body of a fish swimming eastward across the sky. A handful of stars to the west have also been lost to this constellation, and for this reason the Flamsteed numbers 1, 2 and 3 Piscis Austrini refer to stars now formally held within neighbouring Microscopium.

This region of the sky is the source of minor meteor shower, the Piscis Austrinids. Occurring in July and August each year, this shower has a radiant point near the star Fomalhaut in the eastern part of the constellation. It is not a particularly strong shower, with meteor activity tending to be rather faint and sporadic.

Stars

The stars of Piscis Austrinus are generally faint, with a single emphatic exception. That exception is Fomalhaut or Alpha Piscis Austrini, a first magnitude star that falls among the twenty brightest in the entire sky. Fomalhaut lies at the eastern end of the fish, representing its mouth. In reality it is a white star that is a relatively near neighbour of the Sun at a distance of just 25 light years. Fomalhaut has a complex system, with at least two companion stars, a complex array of circumstellar discs. An object within those discs was at one time thought to be a planet, and given the name Dagon, but is now considered more likely to be an expanding cloud of debris.

The remaining stars that make up the body of the Southern Fish are faint by comparison with Fomalhaut, with magnitudes ranging between +4.2 and +4.5. They are also more distant from the Solar System, ranging between 136 and 490 light years from the Sun.

The southern side of the fish's body is described by a string of five stars running eastward from Fomalhaut. The first of these is a yellow star, Delta Piscis Austrini, and the following four are all white in colour. In sequence these are Gamma, Beta and Mu, with Iota Piscis Austrini marking the fish's tail.

The northern flank of the fish is less well defined, being marked by a single star, blue Epsilon Piscis Austrini, which is - by a narrow margin - the brightest of Piscis Austrinus' stars after Fomalhaut.