Regiomontanus

One of the interesting things about the sundials we display in our gardens and public spaces is the rich tapestry of collaboration behind the apparently simple devices. Mathematicians, astrologers, geographers and astronomers put forward theory after theory through the ages to establish the seemingly simple systems we rely on to measure time. Among these scientists, you’ll find Johannes Müller von Köigsberg – also known as Regiomontanus.

Who Was Regiomontanus?

First things first – why does one guy have two names so wildly different? Well, they're not that different – Regiomontanus is a shorter version of the Latinised name Johannes Müller was known by, Joannes de Regio Monte. Regio Monte is Latin for Königsberg (which means King's mountain), where he was from.

Bavarian by Birth, Regiomontanus began his illustrious career when he entered university in Leipzig at the tender age of eleven. After continuing to study at Alma Mater Rudolfina in Vienna, he graduated in 1457 with a Master of Arts. On leaving university, he set to work building astrolabes for Matthias Corvinus of Hungary and Cardinal Bessarion before designing a portable sundial for Pope Paul II in 1465.

He continued to work closely with Georg von Peurbach, whom he'd befriended and studied under in Austria. And, following Peurbach's death, Regiomontanus worked diligently to translate Ptolemy's Almagest and wrote a number of texts expanding on Ptolemy's theories, as well as what is considered one of the first trigonometry textbooks. In this book, De Triangulis Omnimodus, Regiomontanus put forward the premise that to truly understand astronomy, one must first have a firm grasp of the geometric principles of triangles.

He moved to the intellectual hotbed of Nuremberg, Franconia in 1471. While there, he published the first printed astronomical textbook, Theoricae Novae Planetarum, and also worked to have the first observatory constructed with the financial backing of Bernhard Walther, who sponsored Regiomontanus' printing press.

Regiomontanus' Lasting Contributions

While Regiomontanus was, like Ptolemy, a geocentrist, he did not agree with all Ptolemy's theories. In fact, in 1475, Regimontanus worked with Pope Sixtus IV on the touchy subject of calendar reform. It was Regimontanus' own thinking that, in calendars from 1475 to 1532, there were scores of errors due to changing lunar phases, the length of the year itself and the ecclesiastical calculation of when Easter should fall.

The impact of Regimontanus' publications was widely felt through the years after his death - titans of astronomy like Copernicus, Kepler and Brahe would use the work of Regimontanus as a foundation for their own exploration of astronomical truths. And, in addition to lasting monuments and countless instruments Regiomontanus constructed himself, his almanacs provided a lasting resource for many. For example, new world explorer Christopher Columbus used Regiomontanus' Ephemeris in 1504 to predict a lunar eclipse, effectively intimidating the natives into giving his crew adequate provisions while stranded in Jamaica.

The almanacs Regiomontanus produced were somewhat unique, as they included space for scholars or other observers to enter the actual weather juxtaposed with his predictions. Some of these survive today, and provide a useful glimpse of the accuracy Regiomontanus achieved with the technology available to him at the time.