Beta Piscis Austrini: Double Star in Southern Fish

If you’ve ever traced the soft outline of Piscis Austrinus, the Southern Fish, your eyes have almost certainly landed on its brightest jewel, Fomalhaut. But just a short hop away is Beta Piscis Austrini (β PsA). The star doesn’t command the spotlight, yet it’s a nice optical double star.

Through a telescope or binoculars, Beta PsA shines as a crisp white point around magnitude +4.3. Nearby, about 30 arcseconds away, a fainter star around +7.1 can be spotted with steady seeing. Both glow with the cool, icy sheen of A-type main-sequence stars. Astronomers estimate they lie roughly 140 light-years from Earth.

For nearly two centuries, observers assumed these two stars were physically linked as a genuine binary. Yet, according to Jim Kaler, careful measurements reveal the gap between them has widened by more than 5 arcseconds since 1826. If they were bound in a vast orbit, that kind of movement just wouldn’t happen.

The evidence points to a simple truth: they’re not actually a couple at all.

Still, there’s something endearing about a “binary” that isn’t one. The night sky holds surprises even in the quiet corners. And Beta PsA is one more reason to look a little closer the next time you wander near the mouth of the Southern Fish.

My Observations

Through my telescope, Beta Piscis Austrini appears as a pleasant and accessible double star, with its components clearly separated by about 30 arcseconds. Both stars appear white to my eyes. This is consistent with what most observers report.

In my sketch, I include a faint star sitting farther out in the field, though it turns out to be unrelated to this visual pair. Stelle Doppie notes a third companion star at about 9 arcseconds from the primary, with a magnitude of about +15, but at that faint level it remains just beyond what I can detect during my observations.

Key Stats

Constellation	Piscis Austrinus
Best Viewing	Autumn
Visual Magnitude	+4.28 | +7.12
Separation	30.38″
Position Angle	172.3°
Distance	143 light years
Milky Way Location	Orion Spur
My Viewing Grade	B
Designations	β PsA, 17 Piscis Austrini, HD 213398, SAO 213883, HIP 111188

Sources and Notes

Kaler, J. B. (2009, December 11). Beta PsA. Stars, University of Illinois. http://stars.astro.illinois.edu/sow/betapsa.html

Stelle Doppie. (n.d.). WDS J22315-3221 Beta Piscis Austrini. Retrieved November 18, 2025, from https://www.stelledoppie.it/index2.php?iddoppia=100112

Sketch by Wayne McGraw