On a scorching July afternoon in 1878, at the dawn of the Gilded Age, the moon's shadow descended on the American West, darkening skies from Montana Territory to Texas. This rare celestial event-a total solar eclipse-offered a priceless opportunity to solve some of the solar system's most enduring riddles, and it prompted a clutch of enterprising scientists to brave the wild frontier in a grueling race to the Rocky Mountains. Acclaimed science journalist David Baron, long fascinated by eclipses, re-creates this epic tale of ambition, failure, and glory in a narrative that reveals as much about the historical trajectory of a striving young nation as it does about those scant three minutes when the blue sky blackened and stars appeared in mid-afternoon.