- Brown v. the Board of Education of Topeka was decided. (1954) The Supreme Court unanimously decided that segregating public schools was unconstitutional. It was the first concrete federal action against segregation, and overturned decades of the "separate but equal" precedent set in Plessy v. Ferguson.
- Televised Watergate hearings began. (1973) The Watergate affair was a disaster for President Nixon and captivated the nation for over a year, until Nixon finally resigned to avoid being impeached.
- The first legal same-sex marriage took place in the United States. (2004) Marcia Kadish and Tanya McCloskey were married in Massachusetts on this day as the first legally married same-sex couple in the US. Over 70 other same-sex couples were married on this day as well, sparking a few protests but many more celebrations.
- The antikythera mechanism was discovered. (1902) The antikythera mechanism is thought to be an ancient computer, though archaeologists still debate its exact use. It was discovered by Valerios Stais, who went on to become the National Archaeological Museum of Athens.
- The song Louie Louie was officially declared unintelligible. (1965) Rumors had been going around that the song lyrics were obscene, and parents were beginning to send complaining letters to the government about it. The FBI launched a formal investigation, and after a year declared that the lyrics were "unintelligible at any speed" and therefore could not be considered obscene.
- The WHO declared that homosexuality was not a mental illness. (1990) Homosexuality had previously been classified as a form of mental illness both in World Health Organization documents and the Diagnostic and Statistical Manual of Mental Disorders, a widely used diagnostic tool in the United States.
- Napoleon ordered the annexation of the Papal states. (1809) French forces invaded the papal states, eventually forcing the Pope into exile. The papacy was restored in 1814, when the Napoleonic empire began falling apart.
- The first Kentucky Derby was run. (1875) The event was a big hit from the beginning, with over 10,000 people attending the first race. Aristides, ridden by Oliver Lewis, won the first derby.
- A law requiring sex offenders to register changes of address came into effect. (1996) Sometimes known as Megan's law, the law was intended to help protect unsuspecting neighbors from sex offenders by providing information about their whereabouts, especially if they move into a new neighborhood.
- Charlie Chaplin's body was found. (1978) Grave robbers had stolen the body over two months previously to try to get a ransom for it from his widow. The police caught the two men responsible for stealing the body, and it was dug up and re-interred in a theft-proof grave.