Why a Mathematician Is Chasing Eclipses With Algorithms and Cameras

With custom-built gear, his team seeks to solve a long-standing solar mystery Advanced image-processing software developed by Miloslav Druckmüller combines scores of individual images, captured during a total solar eclipse and painstakingly calibrated. The techniques reveal fine details in the sun’s corona, which is white in this image. The tiny pink shapes seen along portions of the edge of the blacked-out solar disk are prominences, which are extensions of relatively cool plasma that can jut out hundreds of thousands of kilometers into space. The sun hangs lowover the plains of Castile and León, in the north-central region ofSpain. But from a slope of the mountainPico Trigaza, it appears that a few puffy white clouds have started to block the sun. That’s vexing. A group of researchers, some wearing cardboard eclipse glasses, is clustered around sets of portabletelescopesand cameras connected to laptops. All this gear is scattered on tabletops perched on the mountainside. On the computer screens, the sun’s disk looks like a deep orange crescent that is slowly waning. That’s because themoonbegan to crawl across it about half an hour ago. In 25 minutes, it will obscure the sun completely, producing an eerie and wondrous phenomenon—a totalsolar eclipse. In the late-summer, late-afternoon heat, the researchers watch anxiously as those fluffy clouds linger around the sun. From an abandoned hut on the slope a few meters above, where the researchers have set up camp, one of the grad students emerges and nods toward the cloud formation. “Do you think it will dissolve?” he blurts out. “It will.”Miloslav Druckmüllerglances calmly at his group of doctoral candidates, now making final checks of the equipment in preparation for totality. Here in Spain, on this 12th day of August, Druckmüller is getting ready for his 19th solar eclipse. He knows from long experience that weather can turn quickly when the moon’s shadow suddenly pushes the temperature down. Plus, there’s no sense in riling up the grad students any more than they already are. Miloslav Druckmüller led the design and construction of a unique optical instrument that incorporates eight astrocameras. Each is equipped with a spectral filter for sensing and recording specific emission spectra from the solar corona. Each of those spectra, in turn, is associated with a particular ionic species of iron atoms. Because the temperature needed to ionize iron varies depending on the ionic species, analyzing the locations and relative abundance of these ionic species offers valuable insights into the distribution of heat in the corona.Václav Široký During totality, the moon blocks the overwhelming glare of the solar disk, revealing delicate structures in the sun’s outer atmosphere, the corona. Using custom-builttelescopesystems and image-processing techniques that Druckmüller has spent decades developing, the researchers aim to gain insights into the processes in this enigmatic region that is otherwisehard to study. In addition to imaging the visible coronal light, the team will try to track the dispersal of superhot ions of iron into interplanetary space, which could give rare insights into the pattern of heat emanating from the corona. Druckmüller is a professor ofmathematicsandimage processingat theBrno University of Technologyin the Czech Republic and a leading figure in theSolar Wind Sherpas, an international team that studies the sun’s corona during total eclipses. In the solar eclipse world, he is nothing short of a legend, albeit a reluctant one. An image from Miloslav Druckmüller’s first solar-eclipse expedition, to Hungary, vividly shows Baily’s Beads. These elongated white lights along a piece of the left edge of the blacked-out solar disk are caused by beams of sunlight shining through gaps in the irregular lunar surface during the eclipse. The pink shapes are solar prominences, which are jets of plasma extending out into space and held in place by the sun’s intense magnetic field. He photographed his first solar eclipse in 1999, in what he thought would be a one-off lark. During that eclipse, the moon’s deep shadow missed Druckmüller’s native Czechia by just a few tens of kilometers, so he chased it to Hungary with a 30-year-oldSoviet MTO 1,000-millimeter lens. All he remembers from that day is the rush of adrenaline he felt while trying to find the sun in the sky with the lens’s minuscule field of view and keep it in focus for the two minutes of the eclipse. He insists that he has never enjoyed any of the eclipses he has photographed. “In fact, I have never properly seen any of those eclipses. You are just watching the screens, making sure that it’s all doing what it’s supposed to do. There are so many things that can go wrong and you can’t redo it.” A composite sequence of photographs shows the 12 August 2026 solar eclipse as seen from a slope of the mountain Pico Trigaza in Spain. Despite Druckmüller’s outward tranquility on this Spanish hillside, the stakes are high. Just 45 minutes ago, his group heard from their colleagues inIceland, where viewing conditions had promised to be better than in Spain. But a vast low-pressure system had clouded the entire sky, leaving all three Iceland teams without a view. On the Pico Trigaza mountain in Spain, two postgraduate researchers used a laser to get a rough, initial alignment for the tracking mount of an optical instrument. The alignment was necessary to precisely compensate for the Earth’s motion. The corona has been amysteryfor centuries. Though dimmer—by a factor of a million—than the sun’s visible surface, the corona is nevertheless extremelyhot: about a million degrees Celsius compared to 5,500 degrees on the surface. Because the sun’snuclear fusionengine churns at the star’s heart, it might seem that temperatures should fall farther from the core. To observe the faint corona in visible light, researchers must block the sun’s ferocious glare. Specialized telescopes calledcoronagraphsdo this with an opaque disk called an occulter. But because light bends around the occulter’s edges in an effect called diffraction, it must block an area much larger than that of the solar disk to prevent light from spilling over and ruining the images. But doing so means obstructing the inner part of the corona, which harbors the most important processes that underpin the puzzling phenomena of the sun’s upper atmosphere. That’s why total eclipses matter so much to solar physicists. By sheer chance, the moon is exactly the right size and at just the right distance to completely cover the sun during a total solar eclipse. Because the moon is so far away from Earth, the view is not marred by diffraction, and the corona reveals itself nearly all the way down to the sun’s surface. As astrocameras recorded spectral data about the sun’s corona, a laptop computer [on table, at left] displayed the phase of the eclipse. Space probescan image the solar surface in other wavelengths, but those views have limitations, too. Spacecraft such as NASA’sSolar Dynamics Observatorydo see the innermost parts of the corona inextreme ultravioletlight, explainsShadia Habbal, a solar physicist at theUniversity of Hawaiiand leader of theSolar Wind Sherpasproject. “But it cuts off very quickly, so you don’t see its extension into space as well as we can see it in the visible emission lines” during an eclipse. “That’s the biggest advantage,” she says, of solar eclipse photography. The European Proba-3 mission, launched in 2024, simulates total solar eclipses by flying two spacecraft in a formation 150 meters apart with one acting as an occulter and the other as the telescope. The instruments aboard that satellite, however, have limitations compared to the equipment used by the Solar Wind Sherpas team. When Druckmüller developed the film from his 1999 eclipse expedition, the photographs didn’t do justice to the event’s eerie beauty. He spent countless evenings applying his expertise in numerical ima