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Fomalhaut — Star in Piscis Austrinus

HIP 113368; Alpha Piscis Austrini; 24 Piscis Austrini

Magnitude 1.2m Star Piscis Austrinus (PsA) Visible
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About Fomalhaut

Description

Fomalhaut is a white main-sequence star of spectral type A3V at magnitude 1.16, the brightest star in Piscis Austrinus and the 18th brightest in the sky. Located about 25 light-years from Earth, it is famous for its prominent debris disk, which was one of the first to be directly imaged. Fomalhaut has a luminosity of about 16 times solar.

Observing Tips

Fomalhaut is the 'lonely' bright star of the autumn sky — it sits in a sparse region well south of the Great Square of Pegasus, with no other bright stars nearby. This isolation makes it easy to identify. From mid-northern latitudes it is always low on the southern horizon. Best observed September through November.

History

The name Fomalhaut comes from the Arabic 'fam al-hut,' meaning 'the mouth of the fish.' It was one of the four Royal Stars of ancient Persia, marking the winter solstice around 2500 BC. In 2008, Fomalhaut became one of the first stars to have an apparent exoplanet directly imaged by Hubble, though the nature of 'Fomalhaut b' remains debated.

Fun Facts

Fomalhaut's debris ring has been called the 'Eye of Sauron' because of its appearance in Hubble images. The ring's sharp inner edge was originally attributed to a shepherd planet, but the object 'Fomalhaut b' may actually be an expanding dust cloud from a collision between two asteroids rather than a planet.

Observe

1Physical Properties

Magnitude 1.16
Spectral Type A4V
Star Color White (B-V 0.09)
Temperature 8602 K
Radius 1.9 R☉
Distance 25 ly

2Position & Identifiers

RA 22h 57m 39.1s
Dec -29° 37' 20.0"
HR 8728
HIP 113368
HD 216956
SAO 191524
Bayer Alpha
Flamsteed 24 PsA

3How easy to spot?

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Equipment Bortle 3 Bortle 4 Bortle 5
Naked eye Easy Easy Easy
50mm finder Easy Easy Easy
150mm scope Easy Easy Easy
Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Jul – Sep (peak: Aug)

5Survey Image

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Size Comparison

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Spectral Classification

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Hertzsprung-Russell Diagram

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Stellar Lifecycle

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Blackbody Spectrum

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Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

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Stellar Fusion

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15Stellar Notes

CPM with HR 8721.
FOMALHAUT; Os Piscis Meridiani; Os Piscis Notii; Difda al Auwel, the "First Frog."
Diam. = 0.00198 - 0.00210".
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Light Travel Time Machine

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Relativistic Travel

Nearby in the Sky

Other targets within a few degrees — pan your scope a little and keep exploring.

Visibility scores assume a 150 mm Newton at Bortle 4.

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