The ambitious plans to study the sun during April’s solar eclipse

Solar scientists across North America will study April’s total solar eclipse to observe the sun’s strangest part: the corona.

Although it is briefly visible as a bright halo that appears only when it is total, it is a million times dimmer in visible light than the rest of the Sun. The corona is also a million degrees warmer than the sun’s surface, or photosphere, which reaches only about 6,000 degrees Celsius, and extends millions of kilometers into the solar system.

The corona is where the sun’s magnetic field acts on charged particles to form complex shapes called streamers, loops, plumes, etc. Understanding the corona helps us predict the solar wind, the stream of charged particles that is blown into space from the Sun. This is the cause of the aurora borealis, but it’s also a potential threat to astronauts, satellites, and the power grid.

Expectations for the total solar eclipse on April 8th are extremely high. That’s because the total solar eclipse, in which the sun is completely covered, will last up to 4 minutes and 27 seconds, the longest such period on land in more than a decade. We would like to introduce some of the experiments that will be carried out in the future.

solar wind sherpa

Shadia HabalThe solar researcher at the University of Hawaii Institute for Astronomy has been tracking solar eclipses for almost 30 years, using special filters and cameras to measure the temperature of particles from the deepest part of the corona.

Habal’s group, now known as the Solar Wind Sherpas, has traveled to far-flung places, including the Marshall Islands, Kenya, Mongolia, Norway’s Svalbard, Antarctica and Libya. Habal and her team use filters to image the corona during each solar eclipse, some of which last only a few seconds. By studying the different wavelengths of light emitted by charged iron particles in the corona, temperature can be revealed.

Most often, solar physicists who study the corona rely on space observatory coronagraphs, which use telescope disks to block the sun. But these devices obscure the deepest parts of the corona, towers of plasma called prominences and sources of eruptions called coronal mass ejections.

“Observations during totality are very important,” Habal says. There is no other way to continuously observe a portion of the Sun’s atmosphere extending from the surface to at least 5 solar radii. “This is fundamental to understanding how the solar atmosphere originates from the Sun and then spreads out into interplanetary space,” she says. Only then will accurate computer models be devised to simulate the corona and help predict space weather.

In the past few years, Habal’s group has made a surprising discovery. The Sun is currently heading towards her solar maximum in 2025, the most active period of his 11-year cycle when solar winds strengthen. Because the corona appears larger during the maximum solar activity during a total solar eclipse, it was thought that there is a close relationship between the solar cycle and the temperature of the corona. But it may not be that simple.

In 2021, Habal and his colleagues published a study based on observations made during 14 total solar eclipses that suggest: The temperature of the corona does not depend on the solar cycle. The lines of the sun’s magnetic field can open and spread outward in the solar wind, or they can close and become hotter, forming a loop. “We found open magnetic field lines everywhere, regardless of the cycle,” Habal says. This means that the temperature of the corona is almost constant.

high flyer

Observations have been impossible since 2019 due to bad weather. “In 2020 there was rain in Chile and in 2021 there were clouds over the Antarctic ocean, but in 2022 there was no solar eclipse,” Habal said.Team members are on an expedition to Antarctica. Benedict Justen Next time, he suggested, they could fly a kite equipped with a spectrometer that separates light into its component wavelengths.

A NASA-funded kite with a wingspan of 6.5 meters was successfully tested in Western Australia during a total solar eclipse in April 2023. It was launched on a kilometer-long tether attached to a vehicle. “It was truly miraculous,” Habal says. Due to bad weather, the team flew for the first time only 45 minutes before total flight. “It was thrilling.”

If the technology works well on future eclipses, more kites will be deployed in the future, and perhaps cameras will be added. “It’s much easier and cheaper than using balloons,” Habal says. But if things don’t work out, there’s always a backup.

During a total solar eclipse, two WB-57 planes will track each other just southwest of the eclipse’s maximum at 740 kilometers per hour, about one-fourth the speed of the moon’s shadow. At this speed, the total velocity increases from 4 minutes and 27 seconds to more than 6 minutes when viewed from the ground. “The WB-57 is perfect for this purpose because the nose cone has a built-in camera and telescope system that allows it to rotate and point at anything no matter what direction the aircraft is flying. ” says Mr. Amir Caspi At the Southwest Research Institute in Boulder, Colorado, he is in charge of the second WB-57 experiment to study the corona in a different way.

Caspi and his team will use a stable platform to image the eclipse using both a visible-light camera and a high-resolution mid-infrared camera developed by NASA. The latter captures light at seven different wavelengths and helps determine which structures in the corona are emitting their own light and which are just scattering light from the Sun’s surface. “To make these observations, we need to be as high up in the atmosphere as possible,” Caspi said. Infrared radiation is difficult to observe from the ground because it is absorbed by the Earth’s atmosphere.

live streamer

Caspi is also part of the Citizen Continental American Telescope Eclipse (CATE) project. The project is an attempt to create a continuous 60-minute high-definition film using a team of 35 citizen scientists who travel a total path from Texas to Maine. They have the same cameras, telescopes, and training, so they can make exactly the same kinds of observations. “Each team will be spaced out so that each station overlaps with its neighbor,” Caspi said. “If one station can’t get data because of clouds or equipment failure, that’s okay.”

He is hopeful the device will work after it was successfully tested in Western Australia last year. “That was the first solar eclipse I ever saw,” Caspi says. He was busy live streaming on his YouTube, so he only got to watch for a few seconds. “Our devices couldn’t go online, so we spent the entire time holding our phones in front of our faces.”

solar eclipse 2024

On April 8th, a total solar eclipse will pass over Mexico, the United States, and Canada. Our special series covers everything you need to know, from how and when to see a solar eclipse to the strangest solar eclipse experience of all time.

It is hoped that the film will allow scientists to study the complexities of the corona, particularly its shape and how it changes over short periods of time. This builds on his 2017 CATE project, which used his 68 cameras throughout the pass. This time, more sophisticated cameras will be used that are sensitive to different types of polarization.

“Most of the light you see during a totality is actually light from the surface of the sun, which enters the corona and scatters electrons,” Caspi says. This is the K-corona, the bright inner part that overwhelms the light emitted solely from the corona itself. When light is scattered, it forms an angle, which is called polarization. “If we can measure the polarization angle, we can see the 3D structure of the corona, its density, and how it changes over time,” he says.

Because time is scarce during a total solar eclipse, an hour of continuous video can capture processes that take seconds or minutes, such as solar flares and coronal mass ejections, and other details. “The corona is permeated by a complex magnetic field,” Caspi said. “During totality, we don’t see a magnetic field, we see hot plasma trapped along the magnetic field, just like we see iron filings around the magnetic field around a magnet.”