Halley's Comet, May 1910
A unique astronomical event is a surefire way to inspire a doomsday prophecy. Enter Halley's Comet, a ball of icy dust that is visible from Earth every 76 years. When this celestial body was scheduled to make a pass in 1910, the claims of impassioned astronomers at Chicago's Yerkes Observatory inspired fear in a surprising number of people. They insisted that the comet's tail was made of poisonous cyanogen gas, and when Earth passed through it on May 18, the toxic fumes would cause widespread death. Some opportunists tried to profit from the hysteria, selling "comet pills," masks and bottled oxygen intended to help people survive the noxious Armageddon.
As the deadly date approached, some concerned citizens stuffed towels under their doors and covered their keyholes with paper to protect themselves from the gas cloud. Others refused to go to work, choosing instead to stay at home with their families or seek refuge in their churches. Conversely, those not taken by the apocalyptic predictions watched the night pass without incident at rooftop "comet parties" held across the United States.