Manhattanhenge is coming. On May 30th, the sun’s rays will stream dramatically down the avenues of New York City’s central borough.

For New Yorkers used to sunsets hidden behind brick and steel canyons, it will be an awesome reminder of the sun’s beauty and power. But when the sun really puts its power on display, we often can’t see it all, or predict it in advance.–

But the effects can be world-changing. The last truly massive display of Sol’s power happened in 1859, when an invisible wave crashed into the Earth.

Electrons, swept up like so much detritus in the magnetic current, coursed along telegraph wires. When they met an obstacle, like the hand of a telegraph operator, they crashed through …