The eclipses that will darken Spain will illuminate the mysteries of the solar corona.

Danilo Torres points his mobile phone at the horizon on a plain in the middle of Castile and León. On the screen, the augmented reality app shows him how high the sun will be on August 12, 2026, at 8:29 p.m. The first of the great eclipses that can be seen in Spain in the next two years will occur in the late afternoon. In August, sunset doesn't occur until almost an hour later, but Torres is concerned that the sun will be very low—in many places within the path of totality, less than 10 degrees above the horizon—and a house or tree could frustrate observations. However, looking at the screen, he is pleased to see that the landscape in front of him will be completely clear .

“I saw this place online over a year ago and had a feeling it could be useful, but we still needed to check the visibility for the eclipse,” he explains, without hiding his enthusiasm for the location, which is otherwise ideal as an operations center. It's a rural house in the small Burgos village of Padilla de Abajo, and has enough space to set up the observation tents and accommodate a dozen scientists. The house also has a swimming pool, something Torres knows the researchers will appreciate as they brave the Castilian summer heat .

Chilean Danilo Torres is the logistics manager for Solar Wind Sherpas , an international group of scientists who travel the world to observe total eclipses. Joining him in Padilla de Abajo is Professor Shadia Habbal , a researcher at the University of Hawaii and leader of the group. Her visit to our country serves to prepare the ground for observing the total eclipses of 2026 and 2027 , which will be visible from Spain. Over the next few days, they will visit potential locations, speak with mayors and other authorities, and try to tie up every possible loose end so that nothing is left to chance.

However, no matter how meticulous they are, there are things beyond their control. “Of the more than 20 expeditions we've conducted since 1995, about 40% have been thwarted by clouds,” says Habbal. This Syrian-American researcher is an expert in studying the corona, the outermost layer of the Sun. Under normal conditions, it cannot be seen from Earth, as the Sun's center is very bright, obscuring what happens at the edges. But during total eclipses, the Moon blocks the rays of the solar disk, and the corona emerges as a mysterious luminous halo.

Chained Mysteries

Known for centuries, the corona began to be studied in greater detail in the 18th century, with the first astronomical expeditions during eclipses. And although much progress has been made in its understanding since then, it remains the most unknown region of the Sun.

It was a Spanish astronomer, José Joaquín de Ferrer , who gave it its name. Hedid so after the total eclipse of 1806, which he observed from Kinderhook, a small town on the banks of the Hudson River in New York State. He borrowed the term "corona" from Latin, where it has the same meaning as in Spanish, and refers to a wreath or other circular object worn on the head.

A few decades later, the development of spectrometry advanced our understanding of the corona. By breaking down radiation into its various components, the spectrometer provides information about the chemical structure of stars. Each element, such as hydrogen or oxygen, produces specific signals, peaks at certain wavelengths that allow us to infer what it is. But when studying the corona, astronomers encountered a surprise.

In 1869, following a total eclipse visible from North America , Charles Young and other astronomers independently observed a mysterious spectral line that did not correspond to any known element. It was proposed that the corona must contain a chemical element unknown on Earth, which was named coronium. Although this idea was later proven wrong, the hypothesis was not unfounded. Around the same time, another unknown spectral line eventually led to the discovery of helium.

The coronium mystery lasted until 1941, when the work of German Walter Grotrian and Swedish Bengt Edlén demonstrated that the unknown element was nothing more than iron. Iron, however, under rather unusual conditions.

In the solar corona, iron atoms appear devoid of half of their electrons. This is such an unlikely form on Earth that until then it was considered a " forbidden transition." Because removing 13 electrons from an iron atom requires temperatures on the order of a million degrees Celsius. These extremely high temperatures occur at the center of the Sun, but even then it was known that the solar surface is much colder, at around 5,500 degrees Celsius. So the answer to the coronium enigma opened a new question: How can the corona be so hot, if the temperature on the solar surface is hundreds of times lower? To this day, the question remains open.

“Coronal heating is the holy grail of solar physics,” says José Carlos del Toro Iniesta , a CSIC research professor at the Institute of Astronomy of Andalusia. Del Toro explains that there must be a mechanism that transfers energy from the lower layers of the Sun to the corona, but the details of exactly how that transfer occurs are not entirely clear.

From auroras to Starlink satellites

At first glance, one might think that what happens in the solar corona has little relevance to life on Earth. Nothing could be further from the truth. Del Toro sums it up in one sentence: "We live in the Sun's atmosphere."

The Sun is made of plasma, a type of high-temperature gas where elements are ionized, that is, in the form of electrically charged atoms and free electrons. In the corona, high temperatures cause a portion of this plasma to be constantly released into space in the form of the solar wind . And occasionally, the plasma is ejected more abruptly, in what are known as coronal mass ejections.

This plasma reaches our planet, where it interacts with the magnetic field surrounding Earth, producing disturbances such as the northern and southern lights, visible from the polar regions. But sometimes, coronal activity can have much more dramatic consequences.

For example, in 1859, a magnetic storm caused by a coronal mass ejection produced auroras visible across half the planet and caused fires and outages at telegraph stations. It is believed that if such a storm were to occur today, the consequences would be much more dramatic , due to our high dependence on electricity and multiple electronic technologies beyond telecommunications. Magnetic storms can induce very intense electrical currents, damaging infrastructure and causing blackouts. This already happened in 1989, when an event of this nature caused a nine-hour blackout in the Canadian province of Quebec.

Satellites are also vulnerable to these disturbances, which can affect communications and navigation systems. Recent research articles warn that the Sun's geomagnetic activity accelerates the reentry of Starlink satellites, reducing their time in orbit.

Only during a total eclipse

Hence, the study of the solar corona is so important. And although space exploration has led to significant advances in recent decades, observing eclipses remains an indispensable tool.

“There is information about the corona that we can only obtain by observing total eclipses,” explains Habbal, while showing an image of the corona obtained from the SOHO satellite using a coronagraph. With the help of this instrument, which blocks sunlight, images of the corona can be obtained without an eclipse. But the coronagraph itself obscures what is happening in the areas closest to the corona, losing valuable information.

Furthermore, despite the logistics required to transport scientists and their equipment around the world, eclipse observation is a much more economical alternative to sending equipment into space.

Although Danilo Torres may be having doubts now, as he tries to confirm his reservation for the cottage. The owner must have noticed his enthusiasm for the place and is hesitant to finalize the deal. “She says she'll let us know,” Torres says with a laugh. “Our suspicion is that she wants to do some research first. We hope it's a reasonable price.”