April 28

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  1693: Gottfried Wilhelm Leibniz writes to L'Hospital, announcing his discovery of determinants fifty years before Cramer, who was the real driving force in the development of determinants. Leibniz's work had little or no influence because it was not published until 1850 in his Mathematische Schriften.

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  1774: Astronomer Francis Baily born. He will observe "Baily's beads" during an annular eclipse (1836).

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  1817: Carl Friedrich Gauss writes to the astronomer H. W. M. Oblers, saying, "I am becoming more and more convinced that the necessity of our (Euclidean) geometry cannot be proved, at least not by human intellect nor for the human intellect."

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  1868: Mathematician Georgy Voronoy born. He will invent what are today called Voronoi diagrams or Voronoi tessellations.

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  1906: Mathematician, philosopher, and academic Kurt Gödel born. His two incompleteness theorems will have an immense impact upon scientific and philosophical thinking in the 20th century.

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  1928: Geologist and astronomer Eugene Merle Shoemaker born. Shoemaker will be the first scientist to conclude that Barringer Meteor Crater in Arizona, and similar craters, were caused by meteor impact.

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  1986: High levels of radiation resulting from the Chernobyl disaster are detected at a nuclear power plant in Sweden, leading Soviet authorities to publicly announce the accident.

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  1999: Physicist and engineer Rolf Landauer dies. Landauer discovered that in any logically irreversible operation that manipulates information, such as erasing a bit of memory, entropy increases and an associated amount of energy is dissipated as heat. This phenomenon is now known as Landauer's principle.