Template:Selected anniversaries/August 21
1560: The occurrence at the predicted time of a solar eclipse in Copenhagen turns Tycho Brahe towards a life of observational astronomy.
1660: Physician, mathematician, and engineer Hubert Gautier born. Gautier will author the first book on bridge building, Traité des Ponts, in 1716, as well as books on roads, fortifications, antiquities, geology, and a first manual for watercolor practitioners.
1909: Mathematician and physicist Nikolay Bogolyubov born. His method of teaching, based on creation of a warm atmosphere, politeness, and kindness, will be renowned in Russia as the "Bogolyubov approach".
1910: Astrophysicist, astronomer, and mathematician Subrahmanyan Chandrasekhar born. He will share the 1983 Nobel Prize for Physics "for his theoretical studies of the physical processes of importance to the structure and evolution of the stars".
1915: Engineer and American intelligence officer Robert Furman born. Furman will be chief of foreign intelligence for the Manhattan Project, directing espionage against the German nuclear energy project, and, near the end of the war, rounding up German atomic scientists.
1945: Physicist Harry Daghlian is fatally irradiated in a criticality accident during an experiment with the Demon core at Los Alamos National Laboratory.
1993: NASA loses contact with the Mars Observer.
2017: The destroyer USS John S. McCain collides with the tanker ship Alnic MC off the coast of Singapore, leaving ten of her crew dead and another five injured.
2017: Dennis Paulson of Mars broadcasts a minute of silence in recognition of the twenty-fourth anniversary of the loss of contact with Mars Observer.