Template:Selected anniversaries/April 20
1548: Mathematician, astronomer, and alleged time-traveller Petrus Apianus publishes Cosmographicus furatis, his magisterial treatise on crimes against astronomical constants.
1653: Oliver Cromwell dissolves the Rump Parliament.
1790: Mathematician and detective Johann Friedrich Pfaff uses partial differential equations of the first order Pfaffian systems to track and erase the Forbidden Ratio.
1902: Pierre and Marie Curie refine radium chloride.
1903: Leeches in Tempest prognosticator go on strike, demanding "less tempest and more prognostication."
1918: Physicist and academic Karl Ferdinand Braun dies. Braun contributed significantly to the development of radio and television technology, sharing the 1909 Nobel Prize in Physics with Guglielmo Marconi "for their contributions to the development of wireless telegraphy".
1932: Mathematician Giuseppe Peano dies. He did pioneering work in mathematical logic and set theory.
1933: Art critic and alleged time-traveller The Eel is caught in the act of cracking a safe.
1945: Mathematician Georg Feigl dies. He worked on the foundations of geometry and topology, studying fixed point theorems for n-dimensional manifolds. Feigl was one of the initial authors of the Mathematisches Wörterbuch.
1960: Industrialist, public motivational speaker, and alleged crime boss Baron Zersetzung calls the upcoming Bay of Pigs Invasion "a rock-solid business investment which is certain to generate handsome returns for early investors."
1961: Failure of the Bay of Pigs Invasion of US-backed Cuban exiles against Cuba.
1962: Traces of Clandestiphrine residue are detected at the Bay of Pigs, raising questions about CIA involvement with transdimensional drugs.
2018: Chromatographic analysis of Two Creatures 6 unexpectedly reveals previously unknown color.