Some potential dangers are close at hand: pandemics, extreme weather, volcanoes and computer viruses, among others. Another one is 93 million miles away: the sun. The life-enabling nuclear fusion ball that Walt Whitman marveled as “O so amazing and broad—up there resplendent, darting and burning!” also holds the power to cause chaos for humanity and its various forms of commerce. The danger comes in the form of solar storms. One such event occurs when the sun releases a blast of plasma called a coronal mass ejection (CME) that arrives at Earth a few days later. Another ejection, known as a solar flare, comprises a burst of radiation traveling at the speed of light. When one of these phenomena hits Earth’s magnetic field and atmosphere, it creates a geomagnetic storm that can cause satellites, transformers, relays, sensors and other equipment vital to power grids, navigation, internet service, defense systems, financial transactions, communications and any number of other operations to fail. A large-scale CME or flare, Forbes reported last year, “would knock out power plants, transmission lines, and substations for entire regions or cities. Huge swaths of the world’s population could be without power for weeks at a time, leading to health crises, food shortages, and devastating economic effects.” Anyone tempted to dismiss such a scenario as science fiction should consider the Carrington Event of 1859, the largest solar storm ever recorded. This CME caused telegraph systems around the world to fail catastrophically. Scientists have found evidence of even larger event in A.D. 774, called the Miyake Event. A geomagnetic storm one-third the size of the Carrington Event hit Quebec, Canada, in 1989, causing the electric grid to collapse and putting 5 million people out of power for nine hours. Twelve years later, scientists detected a...