Игнацио Данти: Математик, Астроном и Реформатор Календаря

Italian Roman Catholic prelate, mathematician, astronomer and cosmographer

Ignazio (or Egnazio) Danti, O. P. (April 1536 – 10 October 1586), born Pellegrino Rainaldi Danti, was an Italian Roman Catholic prelate, mathematician, astronomer, and cosmographer, who served as Bishop of Alatri (1583–1586).

Danti was born in Perugia in 1536 to a family of artists and scientists. As a boy he learned the rudiments of painting and architecture from his father Giulio, an architect and engineer who studied under Antonio da Sangallo, and his aunt Teodora, who was said to have studied under the painter Perugino and also wrote a commentary on Euclid. His older brother Vincenzo Danti became one of the leading court sculptors of late sixteenth century Florence, while his younger brother Girolamo Danti (1547–1580) became a local painter. Danti entered the Dominican Order on 7 March 1555, changing his baptismal name from Pellegrino to Ignazio. After completing his studies in philosophy and theology he spent some time preaching but soon devoted himself zealously to mathematics, astronomy, and geography. although it probably was not completed by the time Danti left Florence. In 1574, Danti used his instruments to calculate the time of the March equinox, an important date for calculating the date of Easter. He discovered that it was 11 days out, falling on the 11 March rather than the 22 March, and he became a leading figure in proposing the reforms that lead to the adoption of the Gregorian calendar in 1582. It is not known precisely why Francesco exiled Danti, but the Dominican had no trouble finding work or patrons anywhere else in Italy, although he never returned to Florence.

After leaving Florence, Danti became a professor of mathematics at the University of Bologna. While there he built a massive gnomon in the Bolognese church of San Petronio, the meridian line of which is still visible on the church's pavement. He also spent some time in Perugia, at the invitation of the governor, where he prepared maps of the Perugian republic. On account of his mathematical skills, Pope Gregory XIII invited him to Rome, appointed him pontifical mathematician and made him a member of the commission for the reform of the calendar. Danti died at Alatri on 10 October 1586, three years into his service.