4/20: Signifies cannabis culture.
1978: Soviet fighters shot Korean Air Lines Flight 902 after it violated Soviet airspace, forcing it to make an emergency landing due to damage.
1989: Last Canadian $1 bills roll off the presses. The passing of the buck came two years after the introduction of the Loonie, bringing an end to 119 years of the paper dollar.
1999: Two seniors killed 12 of their classmates and a teacher before committing suicide at Columbine High School.
2008: American Danica Patrick won the Indy Japan 300, becoming the first woman to win an IndyCar auto race.