On April 28, 1986, the explosion of Reactor Number Four dwarfed the bombs dropped a quarter century earlier at Hiroshima and Nagasaki. Chernobyl's shadow looms larger than those nuclear events that ended humanity's bloodiest war. When the thinnest of Chernobyl's nuclear reactor casings cracked, it pumped into the atmosphere thirty to forty times more radiation than both bombs put together. That hot spray continued burning unabated for three days, creating a radiating cloud which eventually circled the globe. The Swedish saw it first, then the wind reversed and easterly winds shrouded most of the northern hemisphere. The lifetime of that radiation is gauged not in days but in epochs. Its legacy will carry forward half-lives demarked in tens of thousands of years.