the first set of astronomical tables prepared in Christian Europe. They enabled calculation of eclipses and the positions of the planets for any given time based on the Ptolemaic theory (Ptolemaic system), which assumed that the Earth was at the centre of the universe. The introduction states that the work was prepared in Toledo, Spain, for King Alfonso X (Alfonso X) of León and Castile under the direction of Jehuda ben Moses Cohen and Isaac ben Sid. Although no Castilian version survives, internal evidence—they were calculated for 1252, the initial year of the reign of Alfonso, and at the meridian of Toledo—supports the introduction. The tables were not widely known, however, until a Latin version was prepared in Paris in the 1320s. Copies rapidly spread throughout Europe, and for more than two centuries they were the best astronomical tables available. First printed in 1483, the Alfonsine Tables were an important source of information for the young Nicolaus Copernicus (Copernicus, Nicolaus) before his own work superseded them in the 1550s.