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On April 24, 1915, the Ottoman government arrested and deported 235-270 Armenian intellectuals and community leaders from Constantinople, marking the start of what is considered the first genocide of the twentieth century. In the following years, between 600,000 and 1.5 million Armenians were killed or died on death marches through the desert. April 24 is the Armenian Genocide Remembrance Day, recognised by more than 30 countries though Turkey denies it.

On April 24, 1990, NASA launched the Hubble Space Telescope into orbit — whose observations over more than 30 years have revolutionised astronomy. The Hubble discovered that the universe is expanding at an accelerating rate, detected supermassive black holes at the centres of galaxies, and captured images of galaxies more than 13 billion light-years away. Initially a defect in its mirror was corrected in 1993.

On April 24, 1916, the Easter Rising began in Dublin, when about 1,600 Irish republicans took control of the General Post Office and proclaimed the Irish Republic. The rebellion was crushed by British troops within a week, and its leaders were executed. However, the executions turned the leaders into martyrs and accelerated the process that led to Irish independence in 1921.