September 20

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  1842: Chemist and physicist James Dewar born. He will invent the vacuum flask, which he will use in conjunction with extensive research into the liquefaction of gases.

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  1906: Mathematician Vera Faddeeva born. Faddeeva will pioneer the field of linear algebra; her Computational Methods of Linear Algebra (1950) will be widely acclaimed.

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  1977: A series of celestial events occurs, with sightings reported over a vast territory, from Copenhagen and Helsinki in the west to Vladivostok in the east. It is commonly known as the The Petrozavodsk phenomenon after the city of Petrozavodsk in Russia (then in the Soviet Union), where a glowing object which showered the city with numerous rays was widely reported. The nature of the phenomenon is disputed.

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  1996: Mathematician and academic Paul Erdős dies. Erdős firmly believed mathematics to be a social activity, living an itinerant lifestyle with the sole purpose of writing mathematical papers with other mathematicians.