REGIOMONTANUS (1436-1476) , German astronomer, was born at Konigsberg in Franconia on June 6, 1436. His name originally was Johann Muller, but he called himself, from his birthplace, Joh. de Monteregio, an appellation which became mod ified into Regiomontanus. At Vienna, from 1452, he was the pupil and associate of George Purbach (1423-1461), and they jointly undertook a reform of astronomy rendered necessary by the errors they detected in the Alphonsine Tables. In this they were much hindered by the lack of correct translations of Ptolemy's works; and in 1462 Regiomontanus accompanied Cardinal Bessarion to Italy to study a copy of the Almagest. He rapidly mastered Greek at Rome and Ferrara, lectured on Alfraganus at Padua, and com pleted at Venice in 1463 Purbach's Epitome in Cl. Ptolemaei magnam compositionem (printed at Venice in 1496), and his own De Triangulis (Nuremberg, 1533), a treatise on trigonometry. In 1468 he returned to Vienna, and was thence summoned to Buda by Matthias Corvinus, king of Hungary, for the purpose of col lating Greek manuscripts. He also finished his Tabulae Direc tionum (Nuremberg, 1475), essentially an astrological work, but containing a valuable table of tangents.
In 1471 Regiomontanus settled at Nuremberg. Bernhard Wal ther, a rich patrician, became his pupil and patron; and they to gether equipped the first European observatory, for which Regio montanus himself constructed instruments of an improved type (described in his posthumous Scripta, Nuremberg, I544). His ob servations of the great (Halley's) comet of 1472 supplied the basis of modern cometary astronomy. At a printing-press established in Walther's house by Regiomontanus, Purbach's Theoricae plane tarum novae was published in 1472 or 1473 ; a series of popular calendars issued from it, and in 1474 a volume of Ephemerides calculated by Regiomontanus for thirty-two years (1474-1506), in which the method of "lunar distances," for determining the longitude at sea, was recommended and explained. In 1472 Regio montanus was summoned to Rome by Pope Sixtus IV., to aid in the reform of the calendar; and there he died on July 6, 1476.
See P. Gassendi, Vita Jo. Regiomontani (Parisiis, ; and the general histories of astronomy.