Leap Second

On This Day: Sunday June 30, 2013 This is the 181st day of the year, with 184 days remaining in 2013. Fact of the Day: Leap Second June 30 is one of the two times (the other being December 31) when the addition or subtraction of a second from our clock time is allowed to coordinate atomic and astronomical time. The determination to adjust is made by the International Earth Rotation Service of the International Bureau of Weights and Measures at Paris. A leap second is an intercalary, one-second adjustment that keeps broadcast standards for time of day close to mean solar time. Leap seconds are necessary to keep time standards synchronized with civil calendars, the basis of which is astronomical. The announcement to insert a leap second is given whenever the difference between UTC and UT1 approaches one-half second, to keep the difference between UTC and UT1 from exceeding ±0.9 s. After UTC 23:59:59, a positive leap second at 23:59:60 would be counted, before the clock indicates 00:00:00 of the next day. Negative leap seconds are also possible should the Earth's rotation becomes slightly faster; in that case, 23:59:58 would be followed by 00:00:00. Holidays Congo: Independence Day. Guatemala: Armed Forces Day. Sudan: Salvation Revolution Day. Feast day of St. Theobald of Provins, the Martyrs of Rome, St. Emma, St. Bertrand of Le Mans, St. Erentrude, and St. Martial of Limoges. Events 1520 - Montezuma II was murdered as Spanish conquistadors fled the Aztec capital of Tenochtilan during the night. 1572 - Great Britain passed a Poor Law, giving assistance to the poor who were unemployed or vagrant. 1859 - A French acrobat known professionally as Émile Blondin (Jean-François Gravelet) became the first daredevil to walk acrossNiagara Falls on a tightrope. 1864 - President Abraham Lincoln signed the Yosemite Land Grant. 1870 - Ada Kepley became the first female law school graduate. 1906 - The Meat Inspection Act and the Pure Food and Drug Act each became law. 1908 - One of the most powerful, natural explosions in recorded history occurred, in Central Siberia, devastating 70 miles in diameter. 1921 - President Warren Harding appointed former President Howard Taft to be Chief Justice of the U.S. Supreme Court. 1921 - Radio Corporation of America (RCA) was incorporated. 1934 - Nazi leader Adolf Hitler ordered a purge ("Night of the Long Knives") of his own political party, assassinating hundreds of Nazis whom he believed had the potential to become political enemies in the future. 1936 - "Gone With the Wind" was published. 1952 - "Guiding Light" premiered as a television soap opera. 1966 - The National Organization for Women was founded in Washington, D.C. 1971 - Three Soviet cosmonauts who served as the first crew of the world's first space station died when their spacecraft depressurized during reentry. 1982 - The Equal Rights Amendment (passed by Congress in 1972), prohibiting discrimination on the basis of sex, failed to secure ratification by a sufficient number of states to ensure its inclusion in the Constitution of the United States of America. 2002 - Brazil wins its fifth FIFA World Cup title. Births 1934 - Harry Blackstone Jr., American magician. 1957 - Sterling Marlin, American race car driver. 1960 - Murray Cook, Australian vocalist, songwriter, and guitarist. 1966 - Mike Tyson, former American World Heavyweight boxing Champion. 1975 - Ralf Schumacher, German Formula One race car driver. Deaths 1971 - The crew of the Soyuz 11: Viktor Patsayev, Georgi Dobrovolski, and Vladislav Volkov. 1984 - Lillian Hellman, American playwright. 2003 - Buddy Hackett (born Leonard Hacker), American comedian and actor.