The metre was defined in 1983 (Resolution 1 of the 17th meeting of the CGPM) http://astronomy.activeboard.com/t45549631/the-metre/The Medicine Lodge Treaty was signed October 21, 1867http://en.wikipedia.org/wiki/Medicine_Lodge_TreatyThe Aberfan disaster occurred in the Welsh village of Aberfan on Friday 21 October 1966http://en.wikipedia.org/wiki/Aberfan_disasterThe first official planetarium public showing at the Deutsches Museum in Munich, Germany on October 21, 1923 http://en.wikipedia.org/wiki/Max_Wolf#Life_at_the_university
The Ladd Observatory was opened on the 21st October 1891https://en.wikipedia.org/wiki/Ladd_Observatory
Yerkes Observatory was founded on the 21st October 1897http://astro.uchicago.edu/yerkes/The islands of Saint-Pierre and Miquelon were discovered by Europeans on 21 October 1520http://en.wikipedia.org/wiki/Saint-Pierre_and_Miquelon#History
The Battle of Trafalgar, 21 October 1805http://fr.wikipedia.org/wiki/Bataille_de_TrafalgarUSS Constitution was launched in 1797http://astronomy.activeboard.com/t45698183/uss-constitution/The first pair of satellites for Europe's Galileo global navigation satellite system was launched on the 21st October 2011.http://astronomy.activeboard.com/t45405971/galileo-iov/
People
Ronald Ervin McNair, Ph.D. (October 21, 1950 - January 28, 1986) was a NASA astronaut.http://en.wikipedia.org/wiki/Ronald_E._McNairEugene Burton Ely (October 21, 1886 - October 19, 1911) was an aviation pioneerhttp://en.wikipedia.org/wiki/Eugene_Burton_ElyEdward Ball Knobel (21 October 1841 - 25 July 1930) was an English amateur astronomer.http://en.wikipedia.org/wiki/Edward_KnobelRobert Sutton Harrington (October 21, 1942 - January 23, 1993) was an American astronomerhttp://en.wikipedia.org/wiki/Robert_Sutton_HarringtonSrinagarindra (21 October 1900 - 18 July 1995) was a member of the Thai Royal Familyhttp://en.wikipedia.org/wiki/Srinagarindra#StargazerRichard Carlton Meredith (October 21, 1937 - March 8, 1979), was an American writerhttp://en.wikipedia.org/wiki/Richard_C._MeredithSamuel W. Alderson (October 21, 1914 - February 11, 2005) was an inventorhttp://en.wikipedia.org/wiki/Samuel_W._AldersonCarrie Frances Fisher (October 21, 1956 - December 27, 2016) was an American actresshttp://astronomy.activeboard.com/t51255159/carrie-frances-fisher/Wolfgang Ketterle (born 21 October 1957) is a German physicisthttp://en.wikipedia.org/wiki/Wolfgang_KetterleHarry Schultz Vandiver (21 October 1882 - 9 January 1973) was an American mathematicianhttp://en.wikipedia.org/wiki/Harry_VandiverMartin Gardner (October 21, 1914 - May 22, 2010) was an American popular mathematicshttp://en.wikipedia.org/wiki/Martin_GardnerNicolaus Bernoulli (21 October 1687 - 29 November 1759) was a Swiss mathematicianhttp://en.wikipedia.org/wiki/Nicolaus_I_BernoulliEnrico Betti (21 October 1823 - 11 August 1892) was an Italian mathematicianhttp://en.wikipedia.org/wiki/Enrico_BettiAlfred Bernhard Nobel (21 October 1833 - 10 December 1896) was a Swedish chemisthttp://astronomy.activeboard.com/t45698141/alfred-bernhard-nobel-1833-1896/The Valentich disappearance describes an event on 21 October 1978http://astronomy.activeboard.com/t45697958/valentich-disappearance/
NGC Discovered
NGC 5 is a magnitude +14.3 elliptical galaxy discovered by Edouard Stephan on the 21st October 1881.http://astronomy.activeboard.com/t58822134/ngc-5/NGC 47 is a magnitude +13.1 spiral galaxy discovered by Wilhelm Tempel in 1886.http://astronomy.activeboard.com/t58822039/ngc-47/NGC 605 is a magnitude +12.9 spiral galaxy discovered by Edouard Stephan on the 21st October 1881.http://astronomy.activeboard.com/t58822005/ngc-605/NGC 1250 is a magnitude +12.9 spiral galaxy discovered by Lewis A. Swift on the 21st October 1886.http://astronomy.activeboard.com/t58821984/ngc-1250/NGC 1259 is a magnitude +14.3 spiral galaxy discovered by Guillaume Bigourdan on the 21st October 1884.http://astronomy.activeboard.com/t58821968/ngc-1259/
Asteroid (76) Freia was discovered by the astronomer Heinrich d'Arrest on October 21, 1862, in Copenhagen, Denmark.http://en.wikipedia.org/wiki/76_Freia
Asteroid (208) Lacrimosa was discovered by Austrian astronomer Johann Palisa on October 21, 1879, in Pola.http://en.wikipedia.org/wiki/208_Lacrimosa
Comet Ikeya-Seki on October 21,1965, passed just 450,000 km above the Sun's surfacehttp://astronomy.activeboard.com/t45698214/comet-ikeya-seki/
MeteoritesThe Favars (H5) meteorite fell in Midi-Pyrenees, France, on the 21st October 1844.http://astronomy.activeboard.com/t45697980/favars-meteorite/The Hvittis (EL6) meteorite fell in Turku Ja Pori, Finland, on the 21st October 1901.http://astronomy.activeboard.com/t45697975/hvittis-meteorite/