Chernobyl is a town in Ukraine. In 1986 it was still part of the Soviet Union. That year a reactor at the nuclear power station there exploded. In the first days, a few dozen people died from the blast and from a huge amount of radiation — the dangerous energy that comes out of nuclear material. Radioactive dust rose into the air and travelled across many countries. A wide area around the plant had to be emptied, and many more people became ill in the years after. Scholars do not all agree how many later deaths to count, and the tidy first number is tidier than the whole story. When people argue about nuclear power, they sometimes say they do not want “another Chernobyl.” They are using the place as a warning. Though actually, the name is older than the disaster: it comes from a Russian word for a plant, mugwort or wormwood, that grew there. The Ukrainian form is often written Chornobyl; you will see both. It is a real place and a real tragedy, not a metaphor to throw around lightly.