1981 – The "Morbidity and Mortality Weekly Report" of the Centers for Disease Control and Prevention reports that five people in Los Angeles, California, have a rare form of pneumonia seen only in patients with weakened immune systems, in what turns out to be the first recognized cases of AIDS.

1956 – Elvis Presley introduces his new single, "Hound Dog", on The Milton Berle Show, scandalizing the audience with his suggestive hip movements.

This day in history in 1939...  Mexico outlawed the siesta. 
Another privilege taken away from us by "The Man"! 

1495 – A monk, John Cor, records the first known batch of Scotch whisky.

1830 – U.S. President Andrew Jackson signs the Indian Removal Act which denies Native Americans their land rights and forcibly relocates them.

1888 – Nikola Tesla delivers a lecture describing the equipment which will allow efficient generation and use of alternating currents to transmit electric power over long distances.

1941 – Konrad Zuse presents the Z3, the world's first working programmable, fully automatic computer, in Berlin.

1954 – Bill Haley & His Comets release "Rock Around the Clock", the first rock and roll record to reach number one on the Billboard charts.

1949 – EDSAC, the first practical electronic digital stored-program computer, runs its first operation.<

1915 – Babe Ruth, then a pitcher for the Boston Red Sox, hits his first major league home run.

 Red_Dragon wrote: 
Yep.  Less than 10 miles down the road from where I sit.  One of the several schools I attended back in those days.

1970 – The Ohio National Guard, sent to Kent State University after disturbances in the city of Kent the weekend before, opens fire killing four unarmed students and wounding nine others.

1956 – The polio vaccine developed by Jonas Salk is made available to the public.

1981 – Xerox PARC introduces the computer mouse.

1986 – A nuclear reactor accident occurs at the Chernobyl Nuclear Power Plant in the Soviet Union (now Ukraine), creating the world's worst nuclear disaster.

2005 – The first ever YouTube video, titled "Me at the zoo", was published by co-founder Jawed Karim.

1914 – First baseball game at Wrigley Field, then known as Weeghman Park, in Chicago.

1916 – The Chicago Cubs play their first game at Weeghman Park (currently Wrigley Field), defeating the Cincinnati Reds 7–6 in 11 innings.

2014 – NASA's Kepler space telescope confirms the discovery of the first Earth-size planet in the habitable zone of another star.

1939 – The Grapes of Wrath, by American author John Steinbeck is first published by the Viking Press.