Ambitious plan to study the Sun during April’s solar eclipse

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NASA’s WB-57 research jet will be used to study the eclipse

rich caspi

Across North America, solar scientists will study April’s total solar eclipse to look at the sun’s strangest part: the corona.

Seen fleetingly as a bright halo that is visible only during totality, it is millions of times fainter than the rest of the Sun in visible light. The corona is a million degrees hotter than the Sun’s surface, or photosphere, which reaches only 6000 degrees Celsius, and it extends millions of kilometers across the Solar System.

The corona is the place where the Sun’s magnetic field acts on charged particles to form complex shapes, known as streamers, loops and plumes, among other names. Understanding the corona will help us predict the solar wind, the stream of charged particles thrown from the Sun into space. This is what causes the aurora, but it is also a potential threat to astronauts, satellites and power grids.

Expectations are high regarding the total solar eclipse on April 8 as the total solar eclipse – when the Sun is completely covered – will last for 4 minutes and 27 seconds – the longest duration over land in more than a decade. Here are some experiments that are going to happen.

solar wind sherpa

shadiya hubbalA solar researcher at the University of Hawaii Institute for Astronomy has been following solar eclipses for nearly 30 years, using special filters and cameras to measure the temperature of particles from the innermost part of the corona.

Hubble’s group, now known as the Solar Wind Sherpas, has traveled to such far-flung places as the Marshall Islands, Kenya, Mongolia, the Norwegian archipelago of Svalbard, Antarctica and Libya. In each eclipse, some of which last only a few seconds, Hubble and his team use their filters to image the corona. Studying different wavelengths of light emitted by charged iron particles in the corona helps them determine the temperature.

Most of the time, solar physicists studying the corona rely on space-based observatories’ coronagraphs, which use a disk on the telescope to block the Sun. But these instruments mask the innermost part of the corona, the source of towers of plasma, called prominences, and explosions, called coronal mass ejections.

“Observations during totality are critical,” says Hubble. There is no other way to see the part of the Sun’s atmosphere that extends continuously for at least 5 solar radii from its surface. “This is fundamental to understanding how the solar atmosphere originates from the Sun and then expands into interplanetary space,” she says. Only then can accurate computer models be created that simulate the corona and help in predicting space weather.

In the last few years, Hubble’s group has made a surprising discovery. Right now, the Sun is headed toward solar maximum in 2025, the most active point in its 11-year cycle, when the solar wind intensifies. Because the corona appears much larger at maximum extent of the Sun during a total solar eclipse, it was thought that the solar cycle and the temperature of the corona are linked. But it may not be that easy.

In 2021, Hubble and colleagues published research on observations taken during 14 total solar eclipses that suggests The temperature of the corona does not depend on the solar cycle, The Sun’s magnetic field lines can be open, traveling outward with the solar wind, or closed, which are hotter and form loops. “We found open field lines everywhere, regardless of cycle,” says Hubbell. This means that the temperature of the corona remains almost constant.

high flyers

Bad weather has prevented observations since 2019. “There was rain in Chile in 2020, cloudy ocean waters in Antarctica in 2021, and no eclipse in 2022,” says Hubble. He was a member of the team during the expedition to Antarctica. benedict justen Suggested that next time they could fly a kite equipped with a spectrometer, which separates light into its component wavelengths.

The NASA-funded kite, which has a wingspan of 6.5 metres, was successfully tested in Western Australia during the total solar eclipse in April 2023. It was launched on a kilometer long wire attached to a vehicle. “It was pretty miraculous,” says Hubbell. Bad weather meant the team flew it for the first time just 45 minutes before it was fully completed. “It was thrilling.”

A man stands next to a large red and blue kite to study a total solar eclipse

This box-shaped kite will fly a NASA-funded scientific instrument to study a total solar eclipse

Clemens Brumann and Benedict Justen

If the technology works well in an upcoming eclipse, the kites will be deployed more in the future, possibly with cameras added. “It’s much easier and cheaper than using balloons,” says Hubbell. But if it doesn’t work, there’s always a backup.

During the total eclipse, the two WB-57 aircraft will follow each other at a speed of 740 kilometers per hour, about a quarter of the speed of the moon’s shadow, just southwest of the maximum point of the eclipse. At that speed, totality increases from 4 minutes 27 seconds to more than 6 minutes for those observing it from the ground. “The WB-57 is perfect for this because it has a camera and telescopic system in its nose cone that can rotate to point at anything… no matter what direction the aircraft is flying,” They say rich caspi At the Southwest Research Institute in Boulder, Colorado, Joe is in charge of an experiment in the second WB-57 to study the corona in a different way.

Using a stationary platform, Caspi and his team will capture images of the eclipse using both a visible-light camera and a high-resolution mid-infrared camera developed by NASA. The latter will capture seven different wavelengths of light and help determine which structures in the corona emit their own light and which simply scatter light from the Sun’s surface. “We need to be above the atmosphere as much as possible to make those observations,” Caspi says. Infrared light is absorbed by the Earth’s atmosphere and is difficult to observe from ground level.

live streamer

Caspi is also part of the Citizen Continental-America Telescopic Eclipse (CATE) project, an effort using 35 teams of citizen scientists to continuously produce 60-minute high-resolution movies of the totality’s path from Texas to Maine. Identical cameras, telescopes and training so they can make exactly the same types of observations. “Teams will be spaced apart so that each station overlaps with its neighbors,” Caspi says. “If a station doesn’t get data because of clouds or broken equipment, no problem.”

They are hopeful the device will work, as it was successfully tested in Western Australia last year. “That was the first eclipse I saw,” says Caspi, who only got to see a few seconds because he was busy streaming it live on YouTube. “Our devices couldn’t get online, so I spent the whole time with my phone in front of my face.”

ER8EXD Solar eclipse.  The Moon is rotating in front of the Sun.  illustration

solar eclipse 2024

On April 8, a total solar eclipse will pass over Mexico, America and Canada. Our special series covers everything you need to know, from how and when to see it to some of the strangest eclipse experiences in history.

The hope is that the film will allow scientists to study the intricacies of the corona, particularly its shape and how it changes over a short period of time. It is based on the 2017 CATE project, which used 68 cameras along the entire route. This time, it will use more sophisticated cameras that are sensitive to different types of polarized light.

“Most of the light you see during totality is actually light from the sun’s surface that gets into the corona to scatter electrons,” Caspi says. This is the K corona, the bright interior which overwhelms the light coming from the corona itself. As light scatters, it becomes angular, a property called polarization. “If you can measure the angle of polarization, it gives you the 3D structure of the corona, its density and how it changes over time,” he says.

There are time constraints during a total solar eclipse, so a continuous video lasting up to an hour makes it possible to capture processes that take seconds or minutes, such as a solar flare or coronal mass ejection, as well as other details. “The corona is pervaded by a complex magnetic field,” Caspi says. “During totality, we do not see the magnetic field, but rather the hot plasma trapped with it – just as we are able to see iron filings surrounding the magnetic field around a magnet.”


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