Hellenica World


Debris ring around Fomalhaut imaged by
Hubble Space Telescope's coronagraph.
NASA photo.

Observation data
Epoch J2000
Piscis Austrinus
Right ascension 22h 57m 39.1s
Declination −29° 37' 20"
Apparent magnitude (V) 1.16
Spectral type A3 V
U-B color index 0.08
B-V color index 0.09
Radial velocity (Rv) +6.5 km/s
Proper motion (μ) RA: 329.22 mas/yr
Dec.: −164.22 mas/yr
Parallax (π) 130.58 ± 0.65 mas
Distance 25 ± 0.1 ly
(7.66 ± 0.04 pc)
Absolute magnitude (MV) 1.73
Mass 2.3 M
Radius 1.85 R
Luminosity 16 L
Temperature 8,500 K
Age 2 × 108 years
Other designations
α Piscis Austrini, Alp PsA, Alf PsA, 24 PsA,

Gl 881, HR 8728, CD -30°19370, HD 216956,

GCTP 5565.00, LTT 9292, SAO 191524,

FK5 867, HIP 113368.

Database references

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 night time sky. Its name means "mouth of the whale", from the Arabic فم الحوت fum al-ḥawt. It is a class A star on the main sequence approximately 25 light-years (7.7 parsecs) from Earth.

Until about March 2000, Fomalhaut and Achernar were the two first magnitude stars furthest in angular distance from any other first magnitude star in the celestial sphere. Antares, in the constellation of Scorpius, is now the most isolated first magnitude star.


Fomalhaut is believed to be a young star, only 200 to 300 million years old, with a potential lifespan of only a billion years. 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 a disk of dust in a toroidal shape with a very sharp inner edge at a radial distance of 133 AU, inclined 24 degrees from edge-on. The dust is distributed in a belt about 25 AU wide. The geometric centre of the disk is offset by about 15 AU from Fomalhaut, suggesting the presence of a planet perturbing the disk.[1] The disk is sometimes referred to as "Fomalhaut's Kuiper belt". Fomalhaut's disk is believed to be protoplanetary, and emits considerable infrared radiation.

The much-fainter flare star TW Piscis Austrini is located within a light year of Fomalhaut and the two share a common proper motion through the sky. They are believed to be companion stars and may have had a common origin in a star cluster.

Etymology and cultural significance

Fomalhaut, has had various names ascribed to it through time. One such name in common use is the Lonely Star of Autumn, because it is the only first-magnitude star in the autumn sky of mid-northern latitudes. It has been recognized by many cultures of the northern hemisphere, including the Arabs, Persians and Chinese. Archaeological evidence links it to rituals dating back to about 2500 BCE. It is one of the Persians' four "royal stars". The Stregheria religion from Italy, portrays Fomalhaut as a fallen angel and quarter guardian of the northern gate.

* The name Fom al-Haut comes from scientific Arabic فم الحوت fam al-ħūt (al-janūbī) "the mouth of the (southern) fish/whale"

* The Latin names are ōs piscis merīdiāni, ōs piscis merīdionālis, ōs piscis notii "the mouth of the southern fish"

* The name Difda al Auwel comes from the colloquial Arabic الضفدع الأول aḍ-ḍifdiˤ al-’awwal "the first frog" (the second frog is Beta Ceti)


1. ^ Fomalhaut's Kuiper Belt. Sky & Telescope. Retrieved on October 16, 2007.


1. Nature 435, 1067-1070 (23 June 2005) | doi: 10.1038/nature03601


  • Fomalhaut. SolStation. Retrieved on November 23, 2005.
  • ALF Psa. ARICNS. Retrieved on November 23, 2005.

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