WASHINGTON, D.C. — Scientists threw everything they had at the sky during the solar eclipse that swept across much of the United States on April 8, 2024. They deployed high-altitude aircraft, enlisted volunteers to launch weather balloons and snap bright halo-like images of the sun’s corona, and sent ham radio signals back and forth through the atmosphere.
The goal was to get closer to unraveling some of the enduring mysteries of the sun, including why the corona, the sun’s outer atmosphere, is so much hotter than the surface (SN: 5/1/24).
Preliminary results from this host of solar eclipse science experiments were presented December 10 at the American Geophysical Union’s annual meeting. While clouds obscured part of the eclipse path across the United States, teams were able to collect data that will fuel future inquiries. Here’s a closer look at how some of those projects peering into the shadow of the moon went.
Using the total solar eclipse to view the corona
A pair of NASA WB-57 aircraft set out to study the corona by flying within the moon’s shadow along the path of the total eclipse. The spacecraft carried two types of instruments: cameras to capture images of the corona, and spectrometers that measured different wavelengths of light and could trace different structures within the corona based on their temperatures.
While some images from the wing-mounted cameras came out blurry due to unexpected vibrations, the team was still able to capture detailed images of the corona. The spectrometers, mounted in the nose of the aircraft, were not affected.
Meanwhile, stationed along the path of totality from Texas to Maine, 35 observing teams captured images of the sun’s corona from the ground, as part of the Citizen CATE (Continental-America Telescopic Eclipse) project. The goal was to piece together a 60-minute movie that spans the evolution of the corona during that time, said Sarah Kovac, the project leader and an astronomer at the Southwest Research Institute in Boulder, Colo.
The elusive middle corona is the transition zone between the sun’s surface and the heliosphere; it’s also the origin of bursts of charged particles that can sweep toward Earth, potentially disrupting power grids and satellite and radio communications. Normally, it’s too faint to see with telescopes. But the moon’s shadow acts like a natural coronagraph, making details visible, Kovac said.
The project was hampered by cloudy weather along much of the path. Even so, the teams were able to capture over 47,000 images of the corona. A preliminary movie stitched together from images collected at three different sites — in Texas, Missouri and Maine — showed how different parts of the corona were exposed over time.
Using the solar eclipse to investigate gravity waves
Elsewhere along the path of totality, more than 800 students, organized into teams, launched weather balloons into the sky. The hope of the Nationwide Eclipse Ballooning Project was to capture evidence that an eclipse disturbs the atmosphere enough to create ripples called gravity waves (SN: 4/8/24). Thunderstorms and air moving over mountains are known to perturb the atmosphere enough to trigger gravity waves. And researchers suspected that an eclipse might also be a trigger, by producing a sudden cooling that briefly alters the atmosphere’s equilibrium.
A similar effect is seen at sunset each day, said Jie Gong, an atmospheric scientist with NASA’s Goddard Space Flight Center in Greenbelt, Md., who worked on the project. The stable boundary layer between Earth’s lowest atmospheric region, the troposphere, and the next region up, the stratosphere, sinks as the sun sets.
Data from a similar campaign during an October 2023 eclipse seen in the western United States showed that the eclipse had indeed sent ripples through the atmosphere, Gong said. The 2024 data collection was somewhat hampered by the cloudy weather, even as each team gamely launched a balloon every hour for 30 hours.
But student surveys after the project ended showed at least one clear success, Gong said: Before the project, few saw themselves as adept at STEM fields. After participating in the project, nearly all reported seeing themselves as good at STEM.
Hints of what happens in the ionosphere during a total solar eclipse
More than 6,350 amateur “ham” radio operators at hundreds of stations across the United States participated in a study of the effects of the eclipse on Earth’s ionosphere, the charged layer of atmosphere where radio signals can transmit for long distances (SN: 8/13/17).
The event was organized by HAMSci, a citizen science initiative that joins together the ham radio community with space scientists, taking advantage of how radio signals bouncing off the ionosphere can provide insights into that atmospheric layer’s height, density and structure. And that, in turn, can help researchers better understand the connection between space and the upper atmosphere, said the group’s founder Nathaniel Frissell, a space physicist at the University of Scranton in Pennsylvania.
During the eclipse, HAMSci volunteers transmitted over 52 million signals at frequencies from 1 to 30 megahertz. What they saw, Frissell said, was that as the moon’s shadow passed, there was a dip in the density of electrons in the ionosphere. That causes radio waves “to escape into space, and communications to drop.” That effect mimics the drop-off in ionization that happens daily as day turns into night, Frissell added.
The ephemeral change in ionization due to the eclipse briefly enhanced communications sent at lower frequencies, and worsened the radio signals sent at higher frequencies, the group found. The data also revealed that the base of the ionosphere rose in altitude during the eclipse, then returned to its normal altitude afterward.
Probing solar mysteries from space
While total solar eclipses open the door for many people — including citizen scientists — to hunt for clues to the sun’s mysteries, they provide just a snapshot peek. More answers may come from new space-based ways to study the sun’s atmosphere.
NASA’s Parker Solar Probe has dipped into the sun’s atmosphere, seeking the source of solar winds (SN: 6/7/23). The spacecraft will make its closest approach to the sun yet on December 24, when it flies within 6.1 million kilometers of the surface.
Meanwhile, the newly launched European Space Agency’s Proba-3 mission aims to use a pair of spacecraft flying in formation to simulate hundreds of solar eclipses to better study the middle corona (SN: 12/5/24).
