How photos of the April 8 solar eclipse will help us understand the sun’s atmosphere

There is a gap in our view of the sun: Part of its atmosphere is effectively invisible to our telescopes. However, images taken from Earth during a solar eclipse are filling that hole, providing an unprecedented look at our star’s hidden layer.

But capturing these images requires expertise, special equipment and a lot of patience. . One of the few people who can accept and process solar eclipse images so they reveal some of the Czech mathematician’s best sun-protected secrets Miloslav Druckmüller. His amazing depictions of the bright, bright rays and looping magnetic lines that make up the solar corona when it appears to the human eye from the eclipsing sun are well known in solar physics circles.

Druckmüller spoke to from his office at the Brno University of Technology in the Czech Republic a few days before he left for Mexico. Then, in collaboration with researchers from the University of Hawaii, he will oversee a complex imaging campaign during the total solar eclipse on April 8.

Related: How to photograph the total solar eclipse on April 8, 2024

On the eclipse day, there will be 66 cameras equipped with special filters and distributed to three observation centers in Mexico and the United States to capture thousands of images during the eclipse around four minutes. The researchers hope that, from this huge data set, Druckmüller’s specialized image processing will be able to uncover some previously unknown information about the sun’s invisible region.

The blind spot

Made of an extremely thin, charged gas called plasma, the solar corona is the upper part of the the atmosphere of the sun. It is a million times smaller than the underlying photosphere that makes up the visible surface of the sun, so the starlight dwarfs it when viewed in visible light.

To observe the corona, astronomers must obscure the visible solar disk to allow the faint coronal light to be seen against the dark cosmos. To do this, they use an instrument called a coronagraphequipped with an occulter that blocks sunlight.

However, if the premises only covered the visible ones Sun, the diffraction — the bending of the light around an obstacle — would allow the bright light of the photosphere to spill around the edges of the imager and ruin the photographs. Therefore, astronomers use large occluders that cover the inner corona as far as the distance of one solar ray from the surface of the sun.

There is no diffraction due to the moon, however, being just the right size to perfectly cover the solar disk during a total eclipse.

“Any coronagraph trying to imitate a solar eclipse is smaller than an actual solar eclipse,” said Druckmüller. “It’s too close to the telescope, which means it causes diffraction.

Because of these limitations, scientists know very little about the processes that occur in this hidden region.

“If you take images from space telescopes like the Solar Dynamics Observatoryyou can see the surface of the sun in extreme ultraviolet light,” said Shadia Habbal, professor of solar physics at the University of Hawaii and Druckmüller’s collaborator, during a conference in Brno in November 2022. “You can see a bit of seeing a corona projected against the surface, but that is clearly not enough to understand how this plasma spreads into space.”

The crown is the source of the solar wind, the continuous stream of charged particles that spreads throughout the solar system. From time to time, it erupts with huge eruptions called coronal mass ejections, can cause dramatic geomagnetic storms on Earth. Many of the processes that accelerate this solar wind into space occur in the blind spot of the corona: The sun itself.

dead center a black circle emits an array of white light

dead center a black circle emits an array of white light

A chance discovery

In Druckmüller’s solar eclipse images, this hidden region emerges in unprecedented detail. The coronal gas – made mostly of ionized hydrogen and helium, with a smattering of heavier elements, such as iron, magnesium, silicon or calcium – bends around the magnetic field lines of the sun. Elsewhere, it streams into space from large sunspots or active regions and flows from coronal holes where the magnetic field lines are broken.

Druckmüller first experimented with eclipse photography in 1999, when the shadow of the moon visited Central Europe for the first time in 150 years. The Czech Republic was just outside the overall group, and the stormy weather threatened to ruin the experience in many of the closest viewing locations. Druckmüller set out for Hungary, which provided “a perfectly clear sky.”

An expert in mathematical image analysis, Druckmüller spent months perfecting the photographs, trying to create scenes that would mimic the experience a human viewer would have if his eyes could handle the huge difference in brightness between the parts of the corona close to the surface of the sun and remove those larger. At that time, he had no idea that this new “Hobby” would turn into his second career.

“I was just playing with it,” said Druckmüller. “My goal was to create high-quality solar eclipse images. That’s it.”

In the early 2000s, he shared his creations on a personal website. From there, one of the images found its way into a paper by Habbal and colleagues published in a scientific journal. He did not know that they used his image, and they did not know that it was his image.

“It was a complete coincidence,” said Druckmüller. “Someone took it from my website and removed the copyright. I only found out through a friend. I contacted them to sort this out, and we started collaborating. Within a year, we went on tour together. “

a line of photographers stand in the snow, with mountains in the distance to the right.  darkened sky hold a small black point surrounded in brilliant light.a line of photographers stand in the snow, with mountains in the distance to the right.  darkened sky hold a small black point surrounded in brilliant light.

a line of photographers stand in the snow, with mountains in the distance to the right. darkened sky hold a small black point surrounded in brilliant light.

Measuring temperature

Since 1999, Druckmüller has participated in more than a dozen solar eclipse observations. Over the years, the campaigns grew more complex. For the upcoming eclipse, Druckmüller’s team in Brno sent thousands of pounds of special photography equipment, which will be distributed throughout the three observation centers.

As well as capturing the white light of the corona, the researchers can now see the spectral lines of the various energetic ions in the coronal gas. This opens the door for more exciting science.

“Different types of ions emerge at different temperatures, so by imaging spectral lines of different types of ions, we can measure the temperature in different parts of the corona,” said Druckmüller. “It’s very difficult to do that except in the visible part of the spectrum and it can’t really be done with probes in space, which don’t see visible light.”

Druckmüller admitted that the increasing complexity of the observations took some of the fun out of the experience. What was once a thrilling adventure now looks more like an industrial operation.

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“It will take us four days just to assemble all the equipment,” he said. “The eclipse itself causes us a lot of stress because everything has to work just right. I’ll be relieved when I’m back in my office and the hard drive is on my desk to work with.”

Druckmüller hopes to have the first images ready to share with the world and his scientific colleagues in Hawaii two weeks after the eclipse. To process all the data, he said, it would probably take until the next trip.

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