This year's expedition of the international scientific team Solar Wind Sherpas to the USA and Mexico to observe the solar eclipse was exceptional in many respects. Observations of the eleven-year solar cycle have been completed. For the first time, they used a special NASA aircraft, capable of flying at altitudes of about twenty kilometres, to observe the eclipse. A number of beautiful and scientifically valuable images of the solar corona have been created, which will be used by astrophysicists from the University of Hawaii to study the Sun. And never before have so many Brno students set out on an expedition as this year. The results of the fifteenth solar eclipse expedition were presented today by experts from the Faculty of Mechanical Engineering of the Brno University of Technology at a press conference.

The words "rare natural phenomenon" fail to fully describe the atmosphere that prevails during a total solar eclipse. When the entire solar disc hides behind the Moon for a few minutes, the world darkens and a breathtaking spectacle occurs when looking at the sky. During this period, the Sun reveals its solar corona, visible to the naked eye only during a total eclipse.

This year, the band's shadow went across North America, with a total eclipse on April 8. An international scientific team from the Faculty of Mechanical Engineering of the Brno University of Technology and the Astronomical Institute of the University of Hawaii could not miss it. A total of 5 TB of data was created from the observations, which after weeks of work by mathematician Miloslav Druckmüller turned into unique photographs of this year's total solar eclipse.

Observation in the air and on the ground

The big innovation of this year's observation was the use of an aircraft belonging to NASA, which operates a special program in Houston, Texas, focused on research at high altitudes. This is done by three WB-57 aircraft, capable of flying at an altitude of about twenty kilometres. This year, researchers placed their instruments on board one of them.

"These are extremely interesting aircraft. They are similar to U-2 spy planes. NASA uses them today, for example, to study hurricanes. For us, their use is advantageous as they fly above the clouds. An ordinary airliner flying at ten kilometres can still encounter clouds that could thwart the observation of the eclipse. With the WB-57 aircraft, we have 100% certain observation conditions," explains Druckmüller, who processes the collected data using his software and can use mathematically precise methods to obtain the resulting unique images after stitching tens to hundreds of images.

The scientists were given the opportunity to use the special aircraft at relatively short notice, but still, they managed to prepare the necessary instruments and software and the plane with two pilots was able to take off from Houston on April 8. "The software was created by fifth-grade student Matěj Štarha, now a successful graduate of the Brno University of Technology. The day before the eclipse, he was still remotely dealing with technical issues with image transmission, but in the end, it turned out that there was a problem with the USB cable, which is sensitive to the very low temperature that prevails at high altitudes. This problem was also solved and the observation from the aircraft was successful, thanks to Matěj," praises Druckmüller.

Thanks to the successful test, the American-German-Czech research team hopes to have a chance using the aircraft for the next three eclipses. "In Brno, we will work mainly on software development and partly on hardware, our American colleagues have a difficult task to obtain financing. Around a million dollars will be needed every year," Druckmüller adds. The very fact that they had the opportunity to use the aircraft proves that the team is one of the world's best. "We are backed by our achievements and many years of work. We have a unique apparatus for observing heavy ions in the solar corona and we are the only ones in the world who bring similar results from the observation of eclipses. NASA was interested and it seemed reasonable to allow us to use the aircraft for our observations," says Druckmüller, adding that the processing of data from the aircraft will come in the second half of this year.

The weather played with the expedition.

While on board WB-57 they could rely on cloudless skies, on the ground the success of observations depends on the vagaries of the weather. Therefore, the expedition tries to occupy several observation sites and thus increases the chance that they will succeed at least somewhere. Although this year's results of the expedition are good, the weather did not give the researchers anything for free.

In Kerrville, Texas, the observation was completely ruined by an overcast sky. On the other hand, in Sims, Arkansas, the conditions were ideal for the entire 4 minutes and 17 seconds of the eclipse. At these two observation points, four students from the Faculty of Mechanical Engineering participated. So far, so many students have never been sent to any expedition.

"Including students in the team was very beneficial. Not only are they professionally competent as they have passed years of technical study at our faculty, but it was a pleasure to watch them work directly in the field. During expeditions, several things need to be solved on the fly, you need to improvise. It was the invention, energy and tangible sense of responsibility that were incredibly strong in the youngest members of the team," says researcher Jana Hoderová, who was at the observation site in Sims together with students Matěj Štarha, Václav Široký and Jakub Moravec. "The relaxed and creative atmosphere in the Czech part of the team was also admired by Shadia Habbal from the University of Hawaii, who is the head of the entire Solar Wind Sherpas project and who was with her colleagues with us in Sims. She was surprised that everyone was proactively looking for the best solution, that she didn't have to explicitly task anyone and just watched with satisfaction how everything ran smoothly," adds Hoderová.

The biggest fight was fought by the crew in Torreón, Mexico, where the weather forecast was so bad that the local group split up further and some went to try their luck at the city of Canatlán. Even there, in the end, the conditions were difficult: the wind stirred up dust, tore down tents and shattered the equipment. One of Canatlán's observing systems miraculously survived the storm, and the team obtained at least one wide-field image of the eclipse.

"It was practically the first time that we decided to move the fixed site, which normally takes three days to prepare, to another location, knowing that everything would need to be prepared in less than a day," says researcher Pavel Štarha, adding that about the pessimistic weather forecast, they had no other choice. "It was necessary to refocus all 14 lenses, which is difficult to do without a visible solar disk, and there was no certainty that we would be able to complete this task in time. In terms of clouds, the forecast for Canatlán was much better and in the end, this forecast was true. However, the weather conditions were extremely challenging, complicating the entire preparation of the observation apparatus and the observation itself. Even in these conditions, our four-member team consisting of me, Aneta Zatočilová, Amálie Štarhová and Zuzana Druckmüllerová managed to successfully move even such a large observation site to another more suitable place just one day before the eclipse. The success of the whole move is mainly due to the dedication of all team members, who were able to work until they were physically and mentally exhausted," says Pavel Štarha.

Orange Comet

The processed images from the expedition bring new knowledge about the Sun and the Universe. "Very interesting is the captured comet, which is heading towards the Sun. This is nothing exceptional, many similar comets do not survive the passage of the hot Sun and evaporate. What is remarkable about our image is that the comet is not white, but orange," says Druckmüller.

The explanation lies in the particles that the comet, together with the water that forms its typical white tail, releases into space. "They must be particles too small to be affected by a gravitational field, but they must be subjected to radiation pressure. In our opinion, it is a luminous neutral sodium, which, as the comet approaches the Sun, is released in larger quantities and the comet thus "turns orange". For the layman, we can compare it to the colour of old sodium street lamps," explains Druckmüller.

In Simsu, we managed to obtain images of iron ions in the solar corona. "We observe nine, ten and thirteen times ionized iron. This year's images can be compared with last year's observations in Australia. Interestingly, although we are now at the maximum of solar activity, this year the Sun was incredibly calm. At the same time, we can say from the observation of the entire eleven-year solar cycle that while the evolution of the cycle is visible at first glance in the images of the Sun's magnetic field, the composition of the observed ions in the corona does not change much," says Druckmüller.

A unique image of ten times ionized iron in the solar corona taken on April 8, 2024, in the USA, in the state of Arkansas near the city of Sims.	A unique image of the radiation of thirteen times ionized iron in the solar corona. The joint team of FME BUT and the University of Hawaii is the only one in the world that is able to create similar paintings.

The last important finding is the dominant iron ion in the solar corona, which is ten times ionized iron. "Regardless of the phase of the solar cycle, the Fe XI ion is the most common. This finding is perfectly consistent with the observations of the Ulysses spacecraft. This ion has the highest probability of forming at a temperature of about 1,100,000 Kelvin, which means that this is the most common temperature that occurs in the solar corona," concludes Druckmüller.

The Solar Wind Sherpas is an international team of scientists who travel the world to observe and collect data on total solar eclipses. The team, aptly named because of the huge amount of equipment they bring with them to each (usually remote) observation site, is led by Shadia Habbal of the Astronomical Institute in Honolulu, Hawaii. So far, Solar Wind Sherpas has carried out 15 eclipse expeditions, including to India (1995), Syria (1999), Libya (2006), China (2008), the Arctic (2015), Indonesia (2016) and Australia (2023). The next total solar eclipse observable in Europe will be on August 12, 2026, and will be observable in Spain or on the westernmost tip of Iceland. The Czech Republic will not see it until October 7, 2135.

You can find more about Solar Wind Sherpas here.

Pictures of the solar corona by Miloslav Druckmüller can be found here.