On 14 August 2003, North America experienced its biggest ever energy catastrophe: a giant blackout shut down the north-eastern United States and parts of the Canadian province of Ontario. The outage only lasted a few hours, but the event is thought to have cost around $6 billion. And when night fell in New York, the authorities were overwhelmed with calls reporting a strange luminous cloud floating over the city... that was the night many New Yorkers discovered the Milky Way for the first time, usually invisible due to light pollution.