1963 – U.S. civil rights campaigner Dr. Martin Luther King Jr. writes his open letter from Birmingham Jail, sometimes known as "The Negro Is Your Brother", while incarcerated in Birmingham, Alabama, for protesting against segregation.

1943 – Albert Hofmann accidentally discovers the hallucinogenic effects of the research drug LSD. He intentionally takes the drug three days later on April 19.

On this day in history, April 16, 1889, future Hollywood legend Charlie Chaplin is born in London

1923 – Insulin becomes generally available for use by people with diabetes.

On this day in history, April 15, 1865, President Abraham Lincoln passes away

2003 – The Human Genome Project is completed with 99% of the human genome sequenced to an accuracy of 99.99%

1953 – CIA director Allen Dulles launches the mind-control program Project MKUltra.

1955 – The polio vaccine, developed by Dr. Jonas Salk, is declared safe and effective.

On this day in history, April 12, 1954, Bill Haley records 'Rock Around the Clock,' rock's first No. 1 hit

2006 – Iranian president Mahmoud Ahmadinejad announces Iran's claim to have successfully enriched uranium.

1968 – US President Lyndon B. Johnson signs the Civil Rights Act of 1968, prohibiting discrimination in the sale, rental, and financing of housing.

On this day in history, April 11, 1945, US troops enter Buchenwald concentration camp, confront Nazi horrors

2019 – Scientists from the Event Horizon Telescope project announce the first ever image of a black hole, which was located in the centre of the M87 galaxy.

1970 – Paul McCartney announces that he is leaving The Beatles for personal and professional reasons.

1925 – The Great Gatsby by F. Scott Fitzgerald is first published in New York City, by Charles Scribner's Sons.

1815 – The Mount Tambora volcano begins a three-month-long eruption, lasting until July 15. The eruption ultimately kills 71,000 people and affects Earth's climate for the next two years.

1865 – American Civil War: Robert E. Lee surrenders the Army of Northern Virginia (26,765 troops) to Ulysses S. Grant at Appomattox Court House, Virginia, effectively ending the war.

1860 – On his phonautograph machine, Édouard-Léon Scott de Martinville makes the oldest known recording of an audible human voice.

On this day in history, April 9, 1963, Sir Winston Churchill declared honorary US citizen: 'Steadfast friend

Happy "Thatcher is dead" day to all who celebrate