Fomalhaut (α PsA / α Piscis Austrini / Alpha Piscis Austrini) is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the nighttime sky.

Its name means "mouth of the whale", from the Arabic فم الحوت fum al-ħūt. It is a class A star on the main sequence approximately 25 light-years (7.688 parsecs) from Earth.

Fomalhaut is believed to be a young star, only 200 million years old. The surface temperature of the star is around 8500 kelvins. Compared to the Sun, its mass is about 2.3, its luminosity is about 15, and its diameter is roughly 1.7. It is surrounded by an enormous disk of dust in a toroidal shape (5 AU to 90 AU), is believed to be protoplanetary, and emits considerable infrared radiation. A planet, designated Fomalhaut b, has been inferred from analysis of the dust cloud in 1998.

Over history there have been a large number of variations on the star's name. It was first identified in pre-history and there is archaeological evidence that it was part of rituals in 2500s BCE in Persia where it would have been one of the Persians' four "royal stars". In the religion of Stregheria, Fomalhaut is a fallen angel and quarter guardian of the northern gate .

• Right Ascension 22h 57m 39.05s
• Declination -29°37′20″
• Spectral Type A3V
• Apparent Magnitude 1.16
• B-V Colour 0.09