Chasing the Great American Eclipse

By Dr. Amir Caspi and Dr. Dan Seaton

On April 8, 2024, a total solar eclipse cast its shadow from Eagle Pass, Texas, to Houlton, Maine, likely becoming the country’s most viewed celestial event ever.

During the total solar eclipse, the Moon covered the disc of the Sun, creating a few minutes of shade across a 115-mile-wide swath of the United States. This solar eclipse passed over the homes of around 32 million people, including three of the top 10 most populous U.S. cities — San Antonio, Austin and Dallas — as well as Indianapolis, Cleveland and Buffalo. Millions more trekked to the trail of totality, while the Moon blocked at least half of the Sun’s face across most of the rest of the country.

It was an exciting day, because the odds of seeing a total solar eclipse if you cannot travel to one are actually quite small. This eclipse traveled from Mexico to Maine, allowing Southwest Research Institute the unique and rare opportunity to conduct two nearly simultaneous projects to study the solar corona, the Sun’s outer atmosphere. Teams led by SwRI successfully executed two groundbreaking experiments — by land and air — collecting unique solar data from the total eclipse.

ECLIPSE EXPERIMENTS

The Citizen Continental-America Telescopic Eclipse (CATE) 2024 experiment engaged more than 200 community participants in a broad, approachable and inclusive attempt to make a continuous 60-minute high-resolution movie of this exciting event. A nearly simultaneous investigation used unique equipment installed in NASA’s WB-57F research aircraft to chase the eclipse shadow, making observations accessible only from a bird’s-eye view.

Total solar eclipses offer unique opportunities for scientists to study the hot atmosphere above the Sun’s visible surface. When the Moon covers the disc of the Sun, complex and dynamic features of the Sun’s outer atmosphere are made visible in ways not possible or practical by any other means, opening new windows into the understanding of the solar corona. The faint light from the corona is usually overpowered by the intense brightness of the Sun itself, and some wavelengths of light are blocked by Earth’s atmosphere.

The Sun is a ball of hot ionized gas. It has many different layers, but the most visible is the photosphere, or the surface of the Sun, which is about 10,000 F (or 6,000 C). Above that is the Sun’s tenuous outer atmosphere, including the outermost layer, the corona, which extends from just above the solar surface all the way to the edge of our solar system.

With 35 teams of local community participants, or “citizen scientists,” the Citizen Continental-America Telescopic Eclipse (CATE) 2024 project collected next-generation polarized observations during the 2024 total solar eclipse from Texas to Maine. The network of 35 telescopes may provide 60 continuous minutes of totality images. The CATE 2024 experiment addresses compelling open science questions that require the novel dataset provided by multi-point observations across the entire eclipse path.

The corona is millions of degrees, hundreds of times hotter than the visible surface below, a curious paradox that is a longstanding scientific mystery. The corona is also one of the major sources of eruptions that cause geomagnetic storms around Earth. These phenomena damage satellites, cause power grid blackouts and disrupt communication and GPS signals, so it’s important to better understand them as the world becomes increasingly dependent on such systems.

Both experiments address two very important solar physics questions: why the corona gets so hot and where the solar wind originates. This constant stream of high-energy particles emitted by the Sun all the time and spreading out into interplanetary space travels faster than it seemingly should. These experiments are looking for where the solar wind is born and where its energy comes from as it propagates through the solar system.

But CATE 2024 also provided a tremendous transformative experience, connecting communities with scientists to document one of the most awe-inspiring cosmic phenomena humans can encounter. It was the ultimate science, technology, engineering and mathematics, or STEM, outreach event, attracting teams of volunteers who then shared what they were doing with their wider community.

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ABOUT THE AUTHORS

Dr. Amir Caspi is an experimental solar astrophysicist specializing in high-energy solar events and the solar corona. He is the principal investigator of the CATE 2024 experiment and observations of the solar corona from aboard NASA’s WB-57 aircraft for the recent total solar eclipse. Dr. Dan Seaton is a solar physicist who specializes in observing and modeling the inner and middle solar corona. He serves as the science lead on the two projects above and is the deputy principal investigator of a proposed solar mission observing the middle corona in extreme ultraviolet wavelengths.