Johannes de Sacrobosco
For the crater, see Sacrobosco (crater).Johannes de Sacrobosco or
Sacro Bosco (
John of Holywood, c.
1195 -
1256) was an
English scholar,
astronomer, and
astrologer who taught at the
University of Paris and wrote the authoritative mediaeval astronomy text
Tractatus de Sphaera.
Although described as English, his birthplace is unknown because Sacrobosco is an otherwise unknown town or region. The traditional belief that he was born in
Halifax is now considered discredited because Halifax means 'holy hair', not 'holy wood'. He was educated at
Oxford University. According to a
seventeenth century account, he arrived at the University of Paris on
June 5,
1221, but whether as an arts student or as a
licentiate (one having a
Master of Arts degree from another university and thus qualified to teach) is unclear. In due course, he became a
Professor of
Mathematics at the University of Paris. About
1230, his most well known work,
Tractatus de Sphaera, was published. In this book, Sacrobosco discussed the
Earth and its place 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. In his
Algorismus, theorized to have been his first work, Sacrobosco showed himself to be a strong proponent of
Arab methods of mathematics, being one of the first Western Europeans to use
Arabic numerals and
sexagesimal notation.
What Sacrobosco may be most famous for is his criticism of the
Julian calendar. In his book on
computus,
De Anni Ratione (1235), 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. In this book, he invented the false notion that
Caesar Augustus took a day from February to give to August (see
Julian calendar).
The
lunar crater Sacrobosco is named after him.
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Johannes de Sacrobosco
