1949: Twenty-six of 32 Irish counties officially left the British Commonwealth and became the Republic of Ireland.
1965: The Ford Mustang was introduced to the North American market, dealing a mortal blow to the Ford Falcon line, which was finally discontinued in 1970.
1969: Sirhan Bishara Sirhan (born 1944) was convicted of assassinating Robert F. Kennedy (1925-1968).
1973: George Lucas (born 1944) began writing The Star Wars.
2014: NASA’s Kepler space observatory confirms the discovery of the first Earth-size planet in the habitable zone of another star.
1912: The Cunard liner RMS Carpathia brought 705 survivors from the RMS Titanic to New York City.
1923: Yankee Stadium, “The House that Ruth Built,” opened.
1924: Simon & Schuster published the first crossword puzzle book.
1981: The Pawtucket Red Sox and Rochester Red Wings, two teams from the Triple-A International League, played the longest game in professional baseball history. It lasted for 33 innings, over eight hours and 25 minutes of playing time. Thirty-two innings were played April 18-19, 1981 at McCoy Stadium in Pawtucket, R.I., and the final 33rd inning was played June 23, 1981. Pawtucket won, 3-2.
1988: The United States launched Operation Praying Mantis against Iranian naval forces in the largest naval battle since World War II.
2005: Cardinal Joseph Ratzinger was elected the 265th Pope of the Roman Catholic Church following the death of Pope John Paul II. The new Pope took the regnal name Benedict XVI.
1828: René Caillié (1799-1838) of France became the first non-Muslim European to enter the town of Timbuktu, Mali, and leave alive.
1836: Congress passed a law creating the Wisconsin territory.
1865: Italian astronomer Angelo Secchi demonstrated for the first time his Secchi disk, which measures water turbidity, aboard L’Immaculata Concezion.
1912: Major League Baseball’s Tiger Stadium in Detroit, and Fenway Park in Boston, opened for the first time.
1916: The Chicago Cubs played their first game at Weeghman Park (later renamed Wrigley Field), defeating the Cincinnati Reds 7-6 in 11 innings.
1926: Western Electric and Warner Bros. announced Vitaphone, a process to add sound to film.
1939: Billie Holiday (1915-1959) recorded the first Civil Rights song, “Strange Fruit.”
1951: Romanian surgeon Dan Gavriliu (1915-2012) performed the first successful surgical replacement of a human organ. He replaced an esophagus using sections of stomach to bypass damaged or deformed tissue.
1972: Apollo 16, commanded by John Young, landed on the moon.
2008: Danica Patrick won the Indy Japan 300 to become the first female driver in history to win an Indy car race.
2010: The Deepwater Horizon oil well exploded in the Gulf of Mexico, beginning an oil spill that would last six months.
1509: Henry VIII ascended the throne of England on the death of his father, Henry VII.
1782: The city that would become Bangkok, Thailand, was founded.
1910: American author Samuel “Mark Twain” Clemens died in Redding, Conn., at age 74.
1926: Britain’s Queen Elizabeth II was born in London.
1934: The “Surgeon’s Photograph,” the most famous photo allegedly showing the Loch Ness Monster, was published in the Daily Mail. (It is revealed to be a hoax in 1999.)
1952: Secretary’s Day (now called Administrative Professionals’ Day) was first celebrated.
1988: The Shroud of Turin—the purported burial shroud of Jesus Christ—underwent carbon dating and was shown to have been made in about 1300.
1989: The Tiananmen Square Protests began in Beijing as 100,000 students gathered in Tiananmen Square to commemorate Chinese reform leader Hu Yaobang.
1992: The first extrasolar planets were discovered by astronomers Aleksander Wolszczan and Dale Frail. They discovered two planets orbiting the pulsar PSR 1257+12.
1876: The first ever National League baseball game was played in Philadelphia.
1970: The first Earth Day was celebrated.
1977: Optical fiber was first used to carry live telephone traffic.
1983: The German magazine Stern claimed that the “Hitler Diaries” had been found in wreckage in East Germany. (The diaries were later revealed to be forgeries.)
1993: Version 1.0 of the Mosaic web browser was released.
1994: Richard Milhous Nixon, 37th U.S. president, died at age 81 in New York.
1564: William Shakespeare is believed to have been born on this date. (He died 52 years later, also on April 23.)
1635: The first public school in the United States, Boston Latin School, was founded in Boston, Mass.
1791: James Buchanan, 15th president, was born near Mercersberg, Pa. (He was the only president to remain a bachelor his entire life.)
1914: The first baseball game was played at Wrigley Field, then known a Weeghman Park, in Chicago.
1961: Born this day, George Lopez, American comedian, actor and talk show host.
1985: Coca-Cola changed its formula and released New Coke. The response was overwhelmingly negative and the original formula was back on the market in less than three months as “Classic Coke.”
2005: The First YouTube video was uploaded, titled “Me at the zoo.”