The solar superstorm of 1859 was the fiercest ever recorded. Auroras filled the sky as far south as the Caribbean, magnetic compasses went haywire and telegraph systems failed.
Ice cores suggest that such a blast of solar particles happens only once every 500 years, but even the storms every 50 years could fry satellites, jam radios and cause coast-to-coast blackouts.
The cost of such an event justifies more systematic solar monitoring and beefier protection for satellites and the power grid.
The authors have reconstructed what happened in 1859, based in part on similar (though less intense) events seen by modern satellites. UTC is Coordinated Universal Time—basically, Greenwich Mean Time.