A star that was spotted in 1892 by one of the most gifted astronomical observers of all time but then apparently vanished has been found again – right where he lost it.

Edward Emerson Barnard was an accomplished astronomer, famous for his discovery in 1892 of a fifth moon of Jupiter, Amalthea, almost three centuries after Galileo Galilei saw the first four. But a few weeks earlier, he had made an enigmatic observation that kept bothering him. A short article he published about it in a journal in 1906 was headlined ““.

What he thought he saw was a star, close to Venus on a morning he had pointed his telescope at that planet, hoping to discover satellites.

He estimated its brightness as 7th magnitude, according to the scale astronomers use, where dimmer objects get a higher number. On a dark night, someone with good eyes can see stars of around 6th magnitude at most.

Barnard looked for the star in the only whole-sky catalogue of the day, the Bonner Durchmusterung. It listed all stars of magnitude 9.5 or brighter, so his 7th magnitude star should have been in it, but wasn’t. And observing again later, it seemed gone. The only star he could find near that position was one of 11th magnitude, about a hundred times less luminous.

Could it have been a large asteroid? “Not Ceres, Pallas, Juno and Vesta which were elsewhere,” he later wrote. Some thought the 11th magnitude star he later saw in a similar position, or another nearby star, might have temporarily brightened. Others speculated that Barnard had been fooled by a “ghost”, a stray reflection of Venus in his telescope. But the mystery remained – until, in December 2024, a group of astronomers decided to get to the bottom of it.

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“On a Zoom meeting I have once a week, called the Asteroid Lunch, I just happened to mention it,” says .

Before long, Hunter, an amateur astronomer based in Arizona and co-founder of the International Dark-Sky Association – now – was part of a group of amateur and professional astronomers examining all the explanations that had been proposed. They found good reasons to reject every one of them.

They were about to give up when group member , an optical engineer at the University of Arizona, decided to once more test the ghost theory by looking at Venus at dawn, as Barnard had done. He did so using a telescope fitted with a vintage eyepiece similar to one that Barnard might have used. He was in for a surprise.

Although Venus wasn’t in the position in the sky where Barnard had observed it in 1892, “immediately in the field, I saw a star”, says Ceragioli. He reasoned that it must be pretty bright to be visible at dawn. But the star map on his computer told him it was actually only 8th magnitude – relatively dim.

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Barnard, the group concluded, had experienced something similar. This suggests that the 7th magnitude star he believed he had seen was actually the 11th magnitude star subsequently documented at the location, which had appeared brighter than it really was in the morning light. Barnard was relatively new to the 36-inch telescope of the on Mount Hamilton in California through which he saw the star next to Venus, and he had no other stars of known brightness in view with which to compare it.

Barnard’s error is forgivable, Ceragioli notes, given that determining a star’s brightness by eye was a special skill in Barnard’s time, developed only by astronomers who studied variable stars, which he never did.

Hunter, too, thinks the astronomer’s reputation is still “pretty perfect. We are all very big Barnard fans. It’s a fairly minor error.”

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A school of American shad may function as a giant ear that enables the fish to hear the ultrasonic clicks of hunting dolphins.

Not many fish species are able to hear ultrasound, says at Florida State University. American shad (Alosa sapidissima) can, and seem to use that ability to evade dolphins, which detect prey by listening for reflections of their clicks. “Very few of the fish found in the stomachs of dolphins are shad,” says Shoele’s student Yanni Giannareas.

Experiments suggest the hearing of individual shad isn’t sensitive enough to pick up on dolphin clicks. But if they swim together, this changes, Shoele says. The team’s computer model suggests the school acts as a finely tuned echo chamber for the incoming sound. The sound waves bounce off the regularly spaced fish, and those reflections interact in such a way that their energy gets concentrated in a regularly spaced pattern as well.

Each fish ends up with a spot of amplified sound right next to it. This enables the American shad to detect a dolphin’s sonar sooner and together start evading it.

Giannareas presented at a meeting of the American Physical Society Division of Fluid Dynamics in Phoenix, Arizona, in November.

David Mann, a biologist who is now president of Loggerhead Instruments, an underwater acoustics firm in Sarasota, Florida, was the first to establish that this shad can hear ultrasound, in a . He isn’t convinced that an individual shad would be clueless about an approaching dolphin.

“The shad ultrasound sensitivity is not super great, but dolphins also click at very high source levels,” he says. “The idea of increasing sensitivity of a school of fish to ambient sounds is interesting and leads one to think about experiments to test it.”

Shoele and Giannareas hope their model will show biologists what to look for. The configuration of a school of American shad could provide evidence for this collective hearing ability. If they are optimising their spacing for sound detection, they would swim in a different formation from, for example, similarly sized tuna, a fish that behave like shad but can’t pick up ultrasound.

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