German astronomer who compiled astronomical tables, translated Ptolemy's Almagest from Greek into Latin, and assisted in the reform of the Julian calendar.
Johannes Müller adopted the name Regiomontanus as a Latinized form of his birthplace Königsberg while studying at Vienna. At the age of 15, he was appointed to the Faculty of Astronomy at Vienna. In 1471 he moved to Nuremberg, where he installed a printing press in his house and so became one of the first publishers of astronomical and scientific literature. He went to Rome in 1475, invited by the pope to assist in amending the notoriously incorrect ecclesiastical calendar.
In 1467, Regiomontanus started compiling trigonometric and astronomical tables, but these too were not published until more after his death. Regiomontanus's Ephemerides 1474 was the first publication of its kind to be printed (by himself); it gave the positions of the heavenly bodies for every day from the year 1475 to 1506.
After Regiomontanus's death, the statement 'the motion of the stars must vary a tiny bit on account of the motion of the Earth' was found in his handwriting. This has led some people to believe that Regiomontanus gave Copernicus the idea that the Earth moves round the Sun.