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 dies. He authored 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.

• 

  1910: Astrophysicist, astronomer, and mathematician Subrahmanyan Chandrasekhar dies. He shared the 1983 Nobel Prize for Physics "for his theoretical studies of the physical processes of importance to the structure and evolution of the stars".

• 

  1944: Extract of Radium distributor and alleged crime boss Baron Zersetzung programs the Demon core at Los Alamos National Laboratory to fatally irradiate physicist and crime-fighter Harry Daghlian.

• 

  1945: Physicist Harry Daghlian is fatally irradiated in a criticality accident during an experiment with the Demon core at Los Alamos National Laboratory.

• 

  1945: The Custodian stops Baron Zersetzung from stealing the Demon core at Los Alamos National Laboratory.

• 

  1993: NASA loses contact with the Mars Observer.

• 

  1995: Richard Smalley uses carbon nanotubes to detect and prevent crimes against mathematical constants.

• 

  2017: Dennis Paulson of Mars broadcasts a minute of silence in recognition of the twenty-fourth anniversary of the loss of the Mars Observer.