On 21 August 1914 there was a total solar eclipse. The phenomenon was visible from northern Europe. https://en.wikipedia.org/wiki/Solar_eclipse_of_August_21,_1914
A total solar eclipse will take place on Monday, August 21, 2017. http://en.wikipedia.org/wiki/Solar_eclipse_of_August_21,_2017
The Consuales Ludi or Consualia is a festival instituted by Romulus, which honours Consus, the god of counselhttp://en.wikipedia.org/wiki/Consualia
The Dan-yr-Ogof cave system was discovered on 21 August, 1912.http://astronomy.activeboard.com/t50528287/dan-yr-ogof-cave/Jarvis Island's first known sighting by Europeans was on 21 August 1821http://en.wikipedia.org/wiki/Jarvis_IslandOn August 21, 1986, Lake Nyos suddenly emitted a deadly cloud of CO2http://astronomy.activeboard.com/t44540509/lake-nyos/
The first successful long flight of the R-7 Soviet missile was made on 21 August 1957https://en.wikipedia.org/wiki/R-7_Semyorka
Gemini 5 (officially Gemini V) was launched on August 21, 1965http://astronomy.activeboard.com/t44540598/gemini-5/The OAO-3 (Copernicus) Orbiting Astronomical Observatory was launched in 1972.http://en.wikipedia.org/wiki/Orbiting_Astronomical_Observatory#OAO-3_.28Copernicus.29The Mars Observer spacecraft was lost on August 21, 1993http://astronomy.activeboard.com/t13162539/mars-observer/
Helmut Graf von Zborowski (August 21 1905 - 16 November 1969) was an Austrian aircraft designerhttp://astronomy.activeboard.com/t58367000/helmut-graf-von-zborowski-1905-1969/Claude Grahame-White (21 August 1879 - 19 August 1959) was an English pioneer of aviationhttp://astronomy.activeboard.com/t50501682/claude-grahame-white-1879-1959/ Barbara Zdunk (1769 - August 21, 1811) was the last woman executed for witchcraft in Europe.http://astronomy.activeboard.com/t50501705/barbara-zdunk-1769-august-21-1811/Baron Augustin-Louis Cauchy (21 August 1789 - 23 May 1857) was a French mathematicianhttp://astronomy.activeboard.com/t44540541/baron-augustin-louis-cauchy-1789-1857/Giacomo Filippo Maraldi (August 21, 1665 - December 1, 1729) was an French-Italian astronomer and mathematician. http://en.wikipedia.org/wiki/Giacomo_F._Maraldi
Placemarker
NGC 6640 was discovered by French astronomer Édouard Stephan on the 21st August 1884. http://astronomy.activeboard.com/t58367956/ngc-6640/NGC 6756 was discovered by German-British astronomer William Herschel on the 21st August 1791.http://astronomy.activeboard.com/t58367965/ngc-6756/NGC 7006 was discovered by German-British astronomer William Herschel on the 21st August 1784.http://astronomy.activeboard.com/t58367971/ngc-7006/
TrES-2b was discovered on the 21st August 2006http://en.wikipedia.org/wiki/TrES-2bTitle: The Structure of Pluto's Atmosphere from the 2002 August 21 Stellar Occultationhttp://adsabs.harvard.edu/abs/2005AJ....129.1718PCassini Titan Flyby (T-104): Radar Looked for the 'Magic Island' in 2014http://saturn.jpl.nasa.gov/mission/flybys/titan20140821/
The KellyHopkinsville encounter was a series of alleged alien encounters in August 1955http://en.wikipedia.org/wiki/Kelly%E2%80%93Hopkinsville_encounter
MeteoritesThe Mount Tazerzait (L5) meteorite fell in Agadez, Niger, on the 21st August 1991.http://astronomy.activeboard.com/t44540744/mount-tazerzait-meteorite/
The Dar al Gani 975 (shergottite) meteorite was found in Libya, on the 21st August 1999.http://astronomy.activeboard.com/t60743859/dar-al-gani-975/