October 20

Baseball great Mickey Mantle born (1931); Congress investigates "Reds" in Hollywood (1947); Tom Petty born (1950); President Herbert Hoover dies (1964); Libyan dictator Muammar Gaddafi killed (2011).

October 19

British Gen. Charles Cornwallis surrenders at Yorktown, effectively ending the Revolutionary War (1781); John Jay becomes first US chief justice (1789); Actor and director Jon Favreau born (1966); Black Monday stock market crash; Dow Jones drops 22.6% in one day (1987).

Carl Frederick Gauss

“It is not knowledge, but the act of learning … which grants the greatest enjoyment.”- Carl GaussCarl Friedrich GaussGaussIn 1801, a newly discovered world disappeared before astronomers could determine where it was going. Giuseppe Piazzi had spotted Ceres in January and followed it for several weeks. Then it vanished into the Sun’s glare. The observations covered only a small stretch of its path, leaving astronomers with a difficult question: where should they point their telescopes when it became visible again? A twenty-four-year-old German mathematician, Carl Friedrich Gauss, set about finding an answer.Gauss had been born in Brunswick in 1777. His mathematical ability drew the support of the local duke, whose funding allowed him to continue his education and pursue research. At nineteen, he discovered how to construct a regular seventeen-sided polygon using only a compass and straightedge, a breakthrough in a problem inherited from ancient Greece. In 1801, he published *Disquisitiones Arithmeticae*, a book that transformed the study of whole numbers. He was already doing work that would secure his place in mathematics. Ceres would carry his reputation beyond it.The difficulty was that seeing a few positions in the sky did not directly reveal Ceres’s orbit around the Sun. Earth was moving too, changing the observer’s viewpoint, and the measurements contained errors. Gauss developed a way to calculate an orbit from the limited observations and predict where Ceres would return to view. Astronomers recovered it near his predicted position. What they then called a planet is now classified as a dwarf planet, but the achievement remains striking: mathematics had supplied a location that observation alone had failed to provide. His prediction could be tested by turning a telescope toward the sky.Gauss became director of the Göttingen observatory in 1807. Over the following decades, he helped measure the Earth, investigated magnetism, and made discoveries across mathematics and physics. His range was extraordinary, but the recovery of Ceres offers perhaps the clearest introduction to his mind. He took an incomplete record, worked out what it could support, and produced an answer others could check.He died in Göttingen in 1855, aged seventy-seven.

October 18

"Moby-Dick" first published (1851); US formally takes possession of Alaska from Russia (1867); inventor Thomas Edison dies (1931); astronauts Jessica Meir and Christina Koch conduct first all-female spacewalk (2019); former Secretary of State Colin Powell dies (2021).

October 17

Actress Rita Hayworth born (1918); Mae Jemison, first Black woman in space, born (1956); Eminem born (1972); Mother Teresa wins Nobel Peace Prize (1979); Earthquake near San Francisco kills 63 (1989).

October 16

Marie Antoinette executed (1793); Author Oscar Wilde born (1854); The Walt Disney Co. founded (1923); Actress Angela Lansbury born (1925); Tony-, Academy-, and Emmy-winning actress Shirley Booth dies (1992).

October 15

"I Love Lucy" airs for first time (1951); Sarah “Fergie” Ferguson, formerly the Duchess of York, born (1959); Black Panther Party is created (1966); Wayne Gretzky becomes all-time NHL points leader (1989); Microsoft cofounder Paul Allen dies (2018).