Beautiful images of the white solar corona and unique images of iron and argon ion radiation. Following weeks of work of mathematician Miloslav Druckmüller of the Faculty of Mechanical Engineering of Brno University of Technology, unique photographs of this year's total solar eclipse have emerged from a huge amount of data. This phenomenon took place on April 20, 2023 over the west coast of Australia, where an international scientific team involving Brno mathematicians and astrophysicists of the University of Hawaii headed to observe it.

"This year we have surpassed anything we have achieved so far. No one else has images of the Sun's white corona in this quantity and quality. And as far as images of spectral lines of iron and argon ions are concerned, they are absolutely unique in the world," says Professor Miloslav Druckmüller of the Institute of Mathematics.

He is the author of the software with which he processes the collected data into images that have no analogues in the world. While for a layman the photographs may simply seem "just beautiful", for astrophysicists from the University of Hawaii they represent a source of valuable information about the brightly glowing surroundings of the Sun made up of hot ionized gas – plasma.

This year's great results are due not only to good weather, which the expedition enjoyed this time, but also to the new technology. Significant improvements have been made in the observation of iron ion radiation in the solar corona. "We bought new filters that, unlike the original ones, that needed to be placed in the thermostat and thus caused a number of issues: we had to keep their temperature at 40 degrees Celsius with fluctuations of maximum of one degree. This meant a lot of power consumption in places where there is typically no connection to the power grid. The new filters do not need a thermostat, they are stable over a huge temperature range," says Druckmüller, adding that the expensive filters were funded by the University of Hawaii. A single new filter costs $ 8,500, or almost 200,000 CZK, and there are eight of them in the whole assembly at one of the observation points.

Further improvement was achieved thanks to the new optics, which, on the contrary, researchers purchased cheaply via the Internet portals. "These are high-end lenses, but designed for the outdated Contax camera. One piece could be bought for between $200 and $300, and thus we bought almost all the remaining supplies in the world," says Druckmüller with a smile. The third improvement was the purchase of new cameras, which replaced the top-notch, but after years already obsolete predecessors. "With earlier cameras, it took one to two seconds for an image to be loaded into the computer's memory, and this way we lost half the time of the eclipse just by transferring data. The new cameras can store dozens of images per second, which means we can use the eclipse time practically to one hundred percent. For example, this year's eclipse lasted for less than a minute, but we could take full advantage of it. In addition, the cameras have ten times better resolution than the original ones, so it is really a big shift," says Druckmüller.

All the colors of the Sun

The Solar Wind Sherpas research team is dedicated to investigating the invisible "colors" of the Sun's corona. Thanks to their own special equipment, which was mentioned above, they observe the behavior of elements that have lost many, often half, of their electrons and emit light in very specific "colors" or wavelengths. The most dominant elements on the Sun are hydrogen and helium. Other elements such as iron, nickel, oxygen, carbon and calcium are also present in the solar corona. Each of them hides the secret of the hot corona surrounding the Sun, in which the solar wind forms. It has a great impact on our planet, causing ionization of the Earth's atmosphere, which is manifested by the appearance of auroras, shortwave reception disturbances or fluctuations and outages in the power grid, which can be very serious.

The Solar Wind Sherpas is an international team of scientists and researchers travelling the world to observe and collect data on total solar eclipses. The team, aptly named because of the sheer amount of equipment they bring with them to each (usually remote) observation site, is led by Prof. Shadia R. Habbal of the Astronomical Institute in Honolulu, Hawaii. To date, Solar Wind Sherpas has conducted 14 eclipse expeditions, including to India (1995), Syria (1999), Libya (2006), China (2008), the Arctic (2015) and Indonesia (2016). The team is one of the few in the world to have exploited the diagnostic potential of observations of coronal emission lines at multiple wavelengths, leading to a number of discoveries and successful scientific publications.

"This year, we managed for the first time to observe nine times ionized argon, which is a great achievement. Since 2008, we have been observing iron and nickel ions. In order to form a given ion, a certain temperature is necessary. Thanks to the observation of ions, we basically have a method to indirectly measure the temperature of the solar corona, which we cannot measure otherwise," explains Druckmüller. Processing an image of a single ionized element means working with more than a thousand input images: some capture the light of the Sun's corona through special filters, others serve as calibration images.

Images processed by a special technique are used to visualize fine structures that ordinary photography cannot capture. For astrophysicists, images are important in combination with data, where the values of individual pixels in the photograph also have an exact physical meaning. "The image, which I am creating, is actually incorrect, it is made to be visible to the human eye by highlighting the structures that cannot be viewed directly because of their very low contrast. Then there is also an image in which practically nothing can be seen, but it is correct in terms of brightness. Only these two images together make sense from a scientific point of view," adds Druckmüller.

Three-quarters of a ton of technology

The expedition began about two weeks before the eclipse with a complete rebuilding of the apparatus, for which the Brno part of the team flew first to Hawaii and from there they continued with American colleagues further to Australia. "We left Hawaii with about half a ton of equipment that had to be custom-cleared first. And another 250 kilograms of previously dispatched equipment were waiting for us in Learmont, Australia," says mathematician Jana Hoderová, who personally participated in the expedition together with her colleague Pavel Štarha and mechatronics student Matěj Štarha.

In Australia, the team split into two groups. Scientists choose this strategy mainly to increase the chance of successful observation, even a single cloud at the wrong time can derail a year-long effort. In addition, if the observation points are far enough apart, dynamic changes in the Sun's corona can be read from the images. This year, the so-called belt of totality stretched only over a small piece of land, so the two teams were relatively close to each other. The main group chose the mainland Exmouth for observation. Jana Hoderová and Matěj Štarha had a much more adventurous experience, when they set off on a small boat to one of the nameless islands in the Lowendal Islands to perform their observations in conditions similar to castaways on a deserted island. Even here, however, everything went well. The proof is a memory disk with two terabytes of data, which Miloslav Druckmüller processed using his software for the following weeks.

For the next total solar eclipse, the team will travel to Mexico next year, where the event will take place on April 8. This time, the eclipse is expected to last for four minutes.

A solar eclipse is an astronomical phenomenon that occurs when the Moon is located between the Earth and the Sun, covering it partially or completely. In the case of a total eclipse, there is significant darkness and cooling on the shadowed part of the Earth, a significant glow of the solar corona is visible around the Moon obscuring the Sun, stars and some planets appear in the sky. A shadow about a hundred kilometers wide darkens the Earth, the temperature drops by several degrees. Not a single sound is heard, not even a bird sings. A total eclipse is only visible from an area of the Earth called the belt of totality. The previous total solar eclipse was observable on December 4, 2021 from Antarctica, where, however, the observations of the Czech scientists were thwarted by bad weather. This year, the eclipse occurred on April 20 and was observable in the Indian and Pacific Oceans, the mainland in Australia "touched" only on the Exmouth Peninsula and nearby islands. The team will have another chance on April 8, 2024, when the belt of totality is to hit Mexico, the USA and Canada. The next total solar eclipse visible directly in Europe will occur on August 12, 2026 and will be visible in Spain or the westernmost parts of Iceland. The Czech Republic will have to wait until October 7, 2135.