As people nationwide turned their eyes to the sky Oct. 14 for the first eclipse to pass over the United States since 2017, Professor of Physics and Astronomy Kristina Lynch—despite having a prime viewing spot in the New Mexican desert—mostly watched the ground.
Amid the low dusky scrub stretching toward the shadowy bulge of the San Andreas Mountains, scientific instruments built in her lab at Dartmouth sat in three towering rockets at NASA’s White Sands Test Facility, primed to complete their long journeys from Hanover into the Earth’s upper atmosphere just as it plunged into near darkness.
Lynch and graduate students in her research group are part of a new NASA mission called Atmospheric Perturbations around the Eclipse Path, or APEP. APEP is studying how the sudden drop in sunlight during an eclipse affects the electrically charged ionosphere that ranges from 50 to 600 miles above the Earth’s surface. Atoms and molecules in this layer shed and gain electrons—a process called ionization—as they’re bombarded by solar radiation during the day.
The ionosphere’s active state makes it a critical conduit for radio waves, GPS signals, and satellite communications, as well as an important factor in satellite launches and commercial spaceflight, Lynch says.
“Understanding how the ionosphere responds to a kick has value in just the beauty of it, in understanding how the world works, but also operationally for the commercial space industry,” she says.
APEP on Saturday, the 14th, launched a total of three rockets into the ionosphere in roughly 35-minute intervals before, during, and after the eclipse. The event was an annular eclipse, meaning that the moon—being farther from the Earth in its orbit—only partially covered the sun and created the characteristic “ring of fire” as sunlight beamed around its edges. A second series of rockets—also carrying Dartmouth instruments—will launch from Virginia during the April 8, 2024, total eclipse, which will pass over northern Vermont and New Hampshire.
With a burst of flame and spiraling trail of white, each rocket climbed skyward over New Mexico this past weekend deploying instruments that measured changes in the ionosphere’s electric and magnetic fields, density, and temperature in response to the eclipse. These data are the first simultaneous measurements of the ionosphere taken from multiple locations during a solar eclipse, according to NASA.
The Dartmouth team built the instrument on each rocket that collects signatures of ion-temperature responses in the lower-altitude ionosphere along the eclipse’s path, Lynch said. The size of a large tomato-sauce can, the cylindrical metal instruments were developed in Lynch’s lab to study the structure of the electromagnetic field that produces auroras, which are her primary research focus.
At night, activity in the ionosphere drops off and the layer’s atoms and molecules become neutral, explained Magdalina Moses, a Guarini School of Graduate and Advanced Studies PhD student in Lynch’s lab who does research on eclipses. Moses, fellow PhD student Jules Van Irsel, Guarini, and undergraduates Maeve Conneely ’25 and Elvio Polanco ’24 worked on building the Dartmouth instruments for the APEP rockets.
Ionization by sunlight stops during an eclipse, too, but, unlike at night, it exhibits a gradient with more activity at the outer edge of the moon’s shadow, known as the penumbra, says Moses, who conducted her graduate research at Virginia Tech on the 2017 total eclipse. Scientists at that time observed a large signature of ion density even in areas where the sun was only partially obscured, and Moses says, “We learned in 2017 that even in the penumbra you can get changes.”
What they didn’t have in 2017 were rockets. Plus, the path of the Oct. 14 eclipse passed over the NASA test facility in Las Cruces, New Mexico. “It’s rare to have an eclipse go so close to a rocket site that you can explore it by means other than radio satellite, which have a limited range,” Moses says. Rockets can “meet eclipses where they are,” she says.
The Dartmouth researchers will analyze the data from their devices and share them with the larger APEP science team, Lynch says. For all their commercial and communications value, the APEP data add another piece to the puzzle of the Earth system, one that scientists can use to build more accurate scientific models of the atmosphere and the Earth’s many physical processes, according to Lynch.
“We want to understand our own world well enough so that we can simulate it,” Lynch says. “If you have a good physical understanding of how the system works, if you’ve got all the physics in your model, then you’ll capture all the reactions correctly. These observations become a validation of the truth of your model. If you kick the system and your estimation captures the result of that perturbation, it’s a good test of your model.”
Beyond the scientific value, there is an innate joy to witnessing an eclipse, says Lynch, who has taken part in several rocket missions studying auroras. Lynch and the rest of the science team arrived at the NASA test site around 1 a.m. Saturday and stayed until around noon just after the launches, running countdowns and checking systems and equipment.
“It was dark, but everyone was engaged,” Lynch says of the early morning gathering. “We had a lot of visitors at the science building, including children. During the eclipse’s peak, everyone was out in the parking lot making crosshatch shadows with their fingers to project images of the eclipse on the ground. It was fun to see the crowd—children, spouses, visiting officials—all playing with the shadows.”
During NASA’s broadcast of the launch, as the final rocket stood in the muted light of the eclipse’s peak, Mission Control radioed APEP’s lead researcher, Aroh Barjatya, professor of engineering physics at Embry-Riddle Aeronautical University, for a status update on the second rocket.
Like the first, it had ejected its payload of Dartmouth- and ERAU-built instruments into the ionosphere where they now spun in open sky, transmitting measurements in real time.
“This rocket looks just as pretty as the first one. It’s spectacular data,” Barjatya said during the broadcast. “It’s both gorgeous outside looking at the sun and gorgeous coming inside and looking at the science data—it’s just outstanding.”
