An eerie phenomenon occurs around eclipse totality. Scientists are trying to unravel the mystery

As the moon slides in front of the sun during a total solar eclipse, a bizarre visual effect often steals the show just seconds before darkness falls. Known as shadow bands, these dark and light ripples look like racing water or phantom serpents gliding across flat surfaces.

For centuries, sky-gazers have reported these faint, shimmering lines, yet science still lacks a definitive answer for why they happen. An upcoming eclipse passing through Russia, Iceland, and Spain is giving researchers a fresh shot at cracking the code.

Challenging the Leading Theory

For decades, the prevailing wisdom has been that shadow bands are caused by atmospheric turbulence. This theory suggests that as the sun is reduced to a tiny sliver, the irregular motion of air currents becomes visible, similar to why stars appear to twinkle at night.

However, David Turnshek, an astronomy professor at the University of Pittsburgh, began questioning this after a 2017 study. His team sent sensors 25 kilometers into the sky on high-altitude balloons, expecting the effect to disappear above the atmosphere.

To their surprise, they detected the signal both on the ground and at high altitudes. "We saw this effect above the atmosphere and on the ground, which meant that the leading theory for shadow bands could be wrong," Turnshek noted.

The Knife-Edge Mystery

The 2017 results pointed toward a different culprit: diffraction-interference. This occurs when light waves bend around a sharp boundary, like a knife edge. In this scenario, the curved rim of the moon acts as that edge, creating bands of light and dark through interference.

Capturing these bands is notoriously difficult. They are too subtle for most cameras to record clearly, and they only appear during the most frantic moments just before totality when most viewers are looking up at the sky rather than at the ground.

A Citizen Science Mission

As the next path of totality nears, experts like Gordon Telepun are advising viewers to look at light-colored, smooth backgrounds to spot the rows. Independent researchers are even asking the public to set up white cardboard sheets to film the event on smartphones.

Turnshek is heading to Spain with electronic detectors in tow, hoping for clear skies. Though he originally planned to go as a tourist, the allure of the mystery was too strong. "I couldn’t help myself," he admitted, hoping a new set of data will finally clarify the ambiguous results of the past decade.