The eclipse can tell us a lot about Earth's atmosphere
The eclipse affords us the opportunity to study Earth's ionosphere, a layer of partially charged gas 90 - 1000 km above the surface that helps to transmit satellite and radio signals around the planet and to protect life here by absorbing the Sun's extreme ultraviolet radiation. Disruptions in the ionosphere — from space weather, for example — can interfere with communication and navigation. During the eclipse, we'll be able to measure how the ionosphere responds to a dramatic reduction of UV radiation (up to 85%) and therefore better understand the details of how the ionosphere works.
A prediction: Recent computer simulations of the upcoming total solar eclipse over the continental U.S. predict the density of electrons in the ionosphere will be reduced by 50%, their temperature will drop by 15%, and the wind structure of parts of the atmosphere will be disturbed. That should produce an effect that can be detected by GPS receivers as far away as South America — a prediction that will be tested during the upcoming eclipse.
The bottom line: The solar eclipse will allow us to answer key questions about Earth's space environment that may in turn ensure the accuracy of vital systems we use daily.