Johannes de Sacrobosco

Johannes de Sacrobosco or Sacro Bosco (John of Holywood, c. 1195 - 1256) was an English scholar who taught at the University of Paris.

Although described as English, his birthplace is unknown because Sacrobosco is an otherwise unknown town or region. The theory that he was born in Halifax, England is now discredited because Halifax means 'holy hair', not 'holy wood'. He was educated at Oxford University. In 1220, Sacrobosco went to Paris to continue his studies. About a year after his arrival in the city, on June 5, 1221, he became a professor of mathematics at the University of Paris. Soon his most well known work, Tractatus de Sphaera, was published. In this his first book, Sacrobosco discussed the place of Earth in the Universe. It was required reading by students in all Western European universities for the next four centuries. Its description of the Earth as a sphere and its popularity exposes the nineteenth-century opinion that medieval scholars thought the Earth was flat as a fabrication. Sacrobosco was a strong proponent of Arabic methods of mathematics.

What Sacrobosco may be most famous for is his criticism of the Julian calendar. In his book De Anni Ratione, he maintained that the Julian calendar was ten days off and that some correction was needed. His plan to fix it was to skip one day every 288 years.

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