How to Spot the ‘Loneliest Star’ in the Autumn Night Sky
Just 25 light-years from Earth, Fomalhaut is surrounded by vast belts of dust that could reveal the gravitational fingerprints of undiscovered worlds.
On an autumn night in the Northern Hemisphere, Fomalhaut appears as a bright pinprick in a field of darkness, far from other bright stars. But the star’s apparent solitude is only part of its story: It sits at the center of an expansive system of dusty belts that may hold clues to worlds we have yet to find.
Fomalhaut’s name comes from the Arabic fam al-ḥūt, meaning “mouth of the fish,” reflecting its place in the constellation Piscis Austrinus, or the Southern Fish. In a tradition attributed to ancient Persia, Fomalhaut is one of four “Royal Stars,” celestial markers associated with the cardinal directions. The star was linked to the south and thus also called the “Watcher of the South.”
Its more contemporary “loneliest star” moniker comes from how it appears in the night sky as viewed from Earth. “Unlike many bright stars that are surrounded by other easily recognizable stars or constellations, Fomalhaut stands out in a region where there aren’t many other bright stars visible,” says Seth McGowan, president of the Adirondack Sky Center & Observatory in Tupper Lake, New York.
But Fomalhaut isn’t truly alone. “It’s about 25 light-years from Earth and is actually part of a multiple-star system,” says McGowan. “But from our perspective here on Earth, it looks like a single bright star surrounded by a vast expanse of darkness.”
Fomalhaut has also drawn astronomers’ attention, though not for its isolation. “What’s particularly exciting about Fomalhaut is that it gives us a chance to see what might be happening in another planetary system,” says McGowan.
In 2023, the James Webb Space Telescope revealed three nested belts of dusty debris around the star, likely left over from comet and asteroid collisions. Two of the belts had never been seen before. Webb’s mid-infrared observations revealed warmer dust closer to the star, helping astronomers map regions earlier observations had not resolved.
“Our own solar system has an asteroid belt between Mars and Jupiter, along with the Kuiper Belt beyond Neptune. Fomalhaut has something similar, but on a much larger scale,” says McGowan. The belts extend some 14 billion miles from the star.
The belts’ shapes and gaps may also hint at planets orbiting Fomalhaut. “We can’t necessarily see the planets themselves, but we may be able to see the effects of their gravity on the material around them,” says McGowan. “It’s a little like seeing ripples in a pond and knowing something disturbed the water.”
Fomalhaut is bright enough to see with the naked eye. “Because there are so few other bright stars nearby, it tends to stand out,” says McGowan.
On a clear autumn evening, look toward the southern horizon for a bright star low in the sky with little else around it. Another way to find it is to locate the Great Square of Pegasus, a prominent pattern of four stars; Fomalhaut lies well below it.
