The Great North American Solar Eclipse: Scientific Experiments

On April 8, 2024, millions of people across North America looked up to witness a rare celestial event. While the public enjoyed the spectacle of the total solar eclipse, scientists treated those few minutes of darkness as a critical research opportunity. NASA and other research institutions launched a coordinated campaign involving high-altitude jets, sounding rockets, and ground-based radars to capture data that is impossible to get at any other time.

Chasing the Shadow at 50,000 Feet

The most high-profile experiment involved chasing the moon’s shadow using two WB-57 Canberra aircraft. These are not standard planes. They are specialized high-altitude research aircraft capable of flying well above commercial air traffic.

NASA deployed these jets to fly along the path of totality. By flying at an altitude of 50,000 feet, the aircraft achieved two distinct advantages over ground-based telescopes:

1. Clearer Vision: At that height, the jets are above most of the Earth’s atmosphere. This means they are above clouds, rain, and the water vapor that usually distorts infrared light. This provided a crystal-clear view of the sun’s outer atmosphere.
2. Extended Time: The moon’s shadow moves across the ground at over 1,500 miles per hour. By flying at roughly 460 miles per hour in the same direction, the pilots were able to keep up with the shadow longer than a stationary observer. This extended the duration of totality from about four and a half minutes to over six minutes for the instruments on board.

These jets were outfitted with instruments mounted in their noses to capture high-resolution images in both visible and infrared light.

The Mystery of the Corona

The primary target for the WB-57 mission was the sun’s corona. The corona is the outermost part of the sun’s atmosphere. It appears as a wispy, white halo during an eclipse.

Scientists have been trying to solve the “coronal heating problem” for decades. The logic of heat suggests that as you move away from a fire, it should get cooler. However, the sun behaves differently:

• The Surface (Photosphere): Roughly 10,000 degrees Fahrenheit.
• The Corona: Can reach temperatures between 2 million and 5 million degrees Fahrenheit.

The experiments conducted by the Southwest Research Institute (SwRI), led by principal investigator Amir Caspi, used the jets to take images of the corona in specific wavelengths. They are looking for evidence of “nanoflares”—tiny, frequent explosions on the sun—that might explain how energy is transferred from the surface to the outer atmosphere, causing this massive temperature spike.

Searching for Vulcanoids and Dust Rings

The darkness of an eclipse provides a unique backdrop for finding objects that are usually blinded by the sun’s glare. The WB-57 mission also included a search for “vulcanoids.”

Vulcanoids are a hypothetical belt of asteroids thought to exist between the sun and Mercury. Because they would be so close to the sun, they are impossible to see from Earth during a normal day. Scientists suspect these objects might be leftovers from the formation of the solar system.

Additionally, the team looked for a dust ring around the sun. Finding this dust or these asteroids would provide clues about how our solar system formed and how dust interacts with the solar wind.

The APEP Sounding Rockets

While the jets monitored the sun from above, another experiment focused on how the eclipse affected Earth’s atmosphere. NASA launched three sounding rockets from the Wallops Flight Facility in Virginia as part of the APEP (Atmospheric Perturbations around Eclipse Path) mission.

The goal was to study the ionosphere. This is an electrified layer of our upper atmosphere situated between 55 and 310 miles above sea level. It is crucial for radio communications and GPS signals.

• The Trigger: The sun’s energy constantly charges the particles in the ionosphere during the day.
• The Event: When the eclipse blocks the sun, that energy source vanishes instantly. This creates a sudden “night” in the middle of the day.
• The Result: The rapid cooling and loss of ionization can create atmospheric waves or ripples.

The three rockets were launched at intervals: one 45 minutes before the peak eclipse, one during the peak, and one 45 minutes after. They measured the density of charged particles and electric fields to see how this sudden sunset affected radio wave transmission.

Citizen Science and Radio Operations

Professional scientists were not the only ones gathering data. The HamSCI (Ham Radio Science Citizen Investigation) project mobilized amateur radio operators across the continent.

During the eclipse, the changes in the ionosphere affect how far radio signals can travel. Sometimes signals travel further, and sometimes they fade out entirely. By having thousands of operators transmit and record signals during the eclipse, researchers created a massive dataset showing exactly how the ionosphere shifted in real-time across the entire continent.

Similarly, the Eclipse Megamovie project gathered photos from over 1,000 volunteers. These images are being stitched together to create a continuous movie of the corona as it appeared from different angles and times along the path from Mexico to Canada. This helps reveal plasma flows and changes in the corona that a single static telescope would miss.

Frequently Asked Questions

Why did NASA use WB-57 jets specifically? The WB-57 can fly at altitudes up to 60,000 feet. This puts the aircraft above 90% of the Earth’s atmosphere, reducing image distortion. It also allows the planes to chase the eclipse shadow, extending the observation time for the onboard instruments.

What is the “coronal heating problem”? This is a major question in astrophysics regarding why the sun’s outer atmosphere (corona) is millions of degrees hotter than its surface (photosphere), despite being further away from the sun’s core.

Did the experiments find the vulcanoids? Data analysis from the April 2024 eclipse is still ongoing. It often takes months or even years for scientists to process the high-resolution images and verify if faint objects like vulcanoid asteroids were captured.

How does an eclipse affect my cell phone or GPS? The eclipse impacts the ionosphere, which can refract or bend radio waves. While modern GPS and cellular networks are robust, the sudden changes in the atmosphere can cause minor signal fluctuations. The APEP rocket mission was designed to measure these exact disturbances to help improve future communication technology.