A Soviet officer who, with the cool application of logic, assessed the appearance of five United States nuclear missiles on his early warning radar screen as a system malfunction and did not report the apparent nuclear attack up his chain of command. The incident occurred in 1983 at a time of high tension between the United States and Soviet Union.
The angle of the sun on high clouds relative to an unusual position of the early warning satellite caused the error. Lt. Colonel Petrov had no other data discrediting the alarm other than a studied opinion that a first strike would be more massive, and a knowledge of previous glitches in the early warning system.
Chilling to think that life as we know it almost ended that day.