The 1859 space weather event: Then and now

The 1859 space weather event, combining the first solar flare ever reported with arguably the largest geomagnetic storm ever observed, provided a dramatic opening to a new area of Sun–Earth studies. Here I describe solar science at the time of the discovery of the flare, recount the observation, and trace the developments that led to the correct interpretation of the 1859 solar-terrestrial event by Bartels in 1937. A “fast forward” takes us to the present time when advances in modeling and increasing concern with space weather have prompted renewed interest in a classic observation.