On August 21, 2017, millions of Americans will witness the first total solar eclipse to cross the continental United States in 99 years. As in all total solar eclipses, the moon will block the sun, revealing its ethereal outer atmosphere—its corona—in a wondrous celestial spectacle.

While hordes of citizens prepare to flock to the eclipse’s path of totality, scientists, too, are staking out spots for a very different reason: to investigate the secrets of the sun’s elusive atmosphere. During the eclipse’s precious seconds of darkness, they will shed light on how our sun works, how it can produce deadly solar storms, and why its atmosphere is so hot.

NOVA investigates the storied history of solar eclipse science and joins both seasoned and citizen-scientists alike as they don their eclipse glasses and tune their telescopes for the eclipse over America. Watch NOVA’s Eclipse Over America, Monday, August 21 at 9PM on KQED 9 and streaming online.