Reardon and his colleagues are traveling to Mazatlán, Mexico, for the 2024 eclipse, where the sky will darken for almost four-and-a-half minutes, and chances of clear skies are very high. There, they will set up telescopes equipped with spectrographs that split light into its component wavelengths.

During totality, they will measure the smearing of the solar spectrum caused by the Sun’s light scattering off fast-moving electrons in the corona. This process is related to the Doppler effect — the same phenomenon that makes an ambulance’s siren change in pitch as it passes by. By connecting the amount of smearing to the velocities of the electrons, they can in turn determine the temperatures in the corona.

A longstanding solar science puzzle is why the Sun’s corona is hotter than the surface just a few thousand kilometers below. These temperature measurements will be another step toward solving the mystery.

Reardon said that testing and preparing his equipment to make sure everything works properly can be stressful, but he hopes to have time to steal a glance at the eclipse for himself.

“If all goes well, you can press the button and the equipment will run for part or most of the eclipse by itself, acquiring the data,” he said. “There’s always time to look up and take in the whole spectacle.”

Chasing the shadow

While a solar eclipse is a great opportunity for scientists to study the Sun’s corona, ground-based observers still have to peer through Earth’s atmosphere to make their measurements. Certain studies are difficult or impossible, like observing the Sun in infrared light, since our atmosphere glows at infrared wavelengths.

Fortunately, there’s a solution: fly high-altitude research planes above most of the atmosphere to get a clearer view.