Medieval meteorological manuscript. 1230 extract from De sphaera mundi, by the Parisian astronomer and monk Johannes de Sacrobosco (circa 1195-1256), with a chart of the seven climatic zones, with the torrid zone at the centre and the poles at the extremes. De sphaera mundi is a short astronomy textbook that was widely read and influential in Europe as an introduction to astronomy. Sacrobosco is also known for writing a short introduction to the Hindu-Arabic numeral system, which became the most widely read introduction to the subject in the later mediaeval centuries. He also correctly described the defects of the then-used Julian calendar and recommended what was essentially the Gregorian calendar.