NASA Plane Films Solar Corona Above the Clouds
NASA's research aircraft WB-57 photographed the Sun's corona above dense cloud cover near Iceland, where an observer on the ground would have seen nothing that day.
The total solar eclipse of August 12 was also observed from an altitude of about 15,000 meters. NASA’s research aircraft WB-57 flew that day over the Atlantic Ocean off the coast of Iceland and photographed the Sun’s corona in nine wavelengths, from visible light to infrared. Below the plane lay a dense cloud cover, meaning the eclipse would not have been visible from the ground at all along that stretch of the flight path.
We covered the announcement of this flight before the eclipse itself, while it was still unclear whether the weather would allow the observation to go ahead. Now the first results are in. The program is led by Amir Caspi of the Southwest Research Institute in Boulder, Colorado, with NASA’s Johnson Space Center in Houston and Langley Research Center in Hampton, Virginia, also taking part in the campaign.
“The eclipse path was mostly over the Atlantic Ocean, in places where clouds are common,” Caspi said in a statement about the flight’s results.
What exactly was recording
The instrument sits in the aircraft’s nose and is called SAMI, a rig of four cameras built at NASA’s Langley Research Center. The cameras shoot at 20 or more frames per second, which makes it possible to track not just the corona’s appearance but also its motion. From that altitude the cameras also pick up infrared wavelengths that lower layers of the atmosphere would otherwise absorb before the light reaches the ground.
The plane chased the Moon’s shadow at roughly 740 kilometers per hour, stretching out the observation time. Totality lasted 2 minutes and 56 seconds as seen from the aircraft, compared with the longest totality available to a ground observer that day, 2 minutes and 18 seconds. The flight collected over 2 terabytes of footage.
At the Sun’s eastern edge, the team spotted a large prominence they had not expected, glowing pink in the hydrogen-alpha line. Prominences are loops of hot, magnetized plasma above the Sun’s surface, and when particles from them reach Earth, they can damage satellites, disrupt GPS navigation and strain the power grid. As after the 2024 eclipse, calibration and analysis of the footage is being led by William Ashfield, also of the Southwest Research Institute.
Why does the corona get hotter than the Sun’s surface?
That question is one of the main reasons flights like this get organized. The corona reaches temperatures close to one million degrees, while the visible surface of the Sun beneath it is far cooler, and the mechanism that sustains that gap is still unexplained. Simultaneous images across multiple wavelengths give researchers material to compare structure and dynamics within the corona, but they do not provide an answer on their own.
The path of totality on August 12 crossed Russia, Greenland, Iceland, Spain and Portugal.
Eighty balloons from Iceland
Alongside the aircraft ran a balloon program led by Angela Des Jardins of Montana State University. From Iceland, 80 balloons were launched, from 18 hours before the eclipse to eight hours after it, to measure the collapse of the atmospheric boundary layer, the part of the air envelope that touches the ground. From Spain, six balloons went up, carrying 360-degree cameras and instruments to measure ozone, whose formation depends on sunlight.
Just before the flight, Caspi told NASA: “The Sun is constantly changing. Every eclipse is different. That’s why we can see things we’ve never seen before.”
The limits of what has been released so far
Everything announced so far concerns how well the recording itself went, not a scientific result. The two terabytes are raw material that still has to go through calibration and processing. The prominence has been described, not measured, so its size, speed and composition cannot be discussed before analysis. One eclipse, however well captured, does not settle the question of coronal heating. It adds one set of measurements to the footage from 2024 and to earlier observations, and any findings will carry weight only once they have been peer reviewed and published.
