Regiomontanus

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Regiomontanus was the Latin name of Johannes Müller von Königsberg (1436–1476), the German astronomer, mathematician, and astrologer whose printed astronomical tables and method of dividing the houses gave Renaissance astrology two of its standard instruments. The name is a Latinizing of his Franconian birthplace, Königsberg; he signed himself, and was read for centuries, as the Latin “man of the king’s mountain.”

He was a prodigy of the new humanist science. Schooled at Leipzig and then at Vienna under Georg von Peuerbach, he took up his teacher’s unfinished project of returning to Ptolemy in the original rather than through medieval intermediaries, and completed the Epitome of the Almagest, a condensed and corrected restatement of Greek mathematical astronomy that later readers, Copernicus among them, used closely. His De triangulis omnimodis set out plane and spherical trigonometry as a subject in its own right. In the astronomy and the astrology of his century these were not separate enterprises: the same tables that fixed planetary positions for the calendar fixed them for the horoscope, and Regiomontanus worked both sides without apology, as nearly every mathematician of the age did.

Two of his productions passed into astrological practice and kept his name. The first is the Ephemerides, day-by-day tables of planetary positions running across years, which he printed at Nuremberg from the press he set up there in the 1470s — among the earliest scientific works produced by movable type. They were reissued and imitated for generations, and a persistent story, hard to verify in detail, has the stranded Columbus carrying a set on Jamaica in 1504 and using its prediction of a lunar eclipse to pressure the island’s Taíno inhabitants into continuing to provision his crew. The second is the system of astrological houses still called Regiomontanus: a way of cutting the celestial sphere into the twelve houses by dividing the celestial equator into equal arcs and projecting them onto the ecliptic. He did not invent the underlying idea, which descends from earlier medieval schemes, but his authority and his tables fixed the method, and it remained one of the dominant house systems in European astrology into the modern period.

What he himself believed about the heavens’ influence is less clear than the tools he left. He cast horoscopes and defended astrology’s mathematical basis, yet he also drafted critiques of careless astrological practice, and scholarship has long debated how much skepticism to read into them. He was summoned to Rome, by some accounts to advise on reform of the calendar, and died there in 1476 at forty, suddenly enough that rumor supplied poison. The calendar he was thought to have worked toward was not corrected for another century.

His afterlife is double. To the history of astronomy he is a restorer of Greek rigor and a forerunner of the printed scientific book; to practicing astrologers he is the name on a house system used every day. The two reputations belong to one man who saw no need to choose between them.

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