May 20

325 – Called by Emperor Constantine, the First Council of Nicaea is formally opened, starting the first ecumenical council of the Christian Church.

1497 – Commissioned by King Henry VII of England, John Cabot sets sail from Bristol aboard his ship Matthew to explore the northern new world to find a route to the west.

1861 – The State of Kentucky proclaims its neutrality in the Civil war on the same day that the State of North Carolina secedes from the Union.

1862 – President Abraham Lincoln signs the Homestead Act into law, opening 84 million acres of public land to settlers.

1873 – Levi Strauss and Jacob Davis receive a U.S. patent for denim jeans secured with copper rivets.

1875 –  17 nations sign the Metre Convention in Paris beginning the process of establishing the International System of Units.

1891 – Thomas Edison displays the prototype of his kinetoscope at the  convention of the National Federation of Women’s Clubs in Washington D.C.

1902 – Cuba gains independence from the United States after being a protectorate since the Spanish-American War.

1927 – Piloting the Ryan NYP Spirit of St. Louis, Charles Lindbergh takes off from Roosevelt Field, New York City, attempting to fly the first solo nonstop flight across the Atlantic Ocean from New York to Paris, and win the $25,000 Orteig Prize

1932 – Piloting a Lockheed Vega 5B, Amelia Earhart takes off from Harbor Grace, Newfoundland, attempting to fly the first solo nonstop flight across the Atlantic Ocean by a female pilot.

1949 – The U.S. Armed Forces Security Agency, the predecessor to the National Security Agency, is established.

1956 – As part of Operation Redwing, the 3.8 megaton Cherokee device, is the first airborne hydrogen bomb dropped over Bikini Atoll in the Pacific Ocean.

1964 – Unable to account for an excess temperature noise on a microwave antenna at the Bell Telephone Laboratory’s Crawford Hill, New Jersey site, Robert Woodrow Wilson and Arno Penzias discover the 4.2°Kelvin cosmic microwave background radiation.

1969 –The Battle of Dong Ap Bia (Hamburger Hill) during the Vietnam War ends with a final victorious frontal assault by U.S. troops.

1983 – The journal Science publishes an article by Luc Montagnier about his discovery of the HIV virus that causes AIDS.

1985 – Radio Martí, part of the Voice of America service, begins broadcasting to Cuba.

1996 – In the case of Romer v. Evans, the Supreme Court, citing the court’s previous ruling in Bowers v. Hardwick in 1986, rules against a law that would have prevented any city, town or county in the state of Colorado from taking any legislative, executive, or judicial action to protect the rights of homosexuals, which is later overturned by Lawrence v. Texas in 2003, and Obergefell v. Hodges in 2015.

2013 – An EF5 force tornado strikes the Oklahoma City suburb of Moore, killing 24 people and injuring 377 others.