I have recently been involved in more that one exchange on the subject as to what tipped the scales in favour of heliocentricity against geocentricity in the Early Modern Period. People have a tendency to want to pin it down to one crucial discovery, observation or publication but in reality it was a very gradual process that took place over a period of at least three hundred and fifty years and involved a very large number of people. In what follows I intend to sketch that process listing some, but probably not all, of the people involved. My list might appear to include people, who at first might not appear to have contributed to the emergence of modern astronomy if one just considers heliocentricity. However, all of those who raised the profile of astronomy and emphasised its utility in the Early Modern Period raised the demand for better and more accurate astronomical data and improved models to produce it. The inclusion of all these factors doesn’t produce some sort of linear progress but more a complex mosaic of many elements some small, some simple, some large and some spectacular but it is not just the spectacular elements that tells the story but a sum of all the elements. So I have cast my nets very wide.

The first question that occurs is where to start. One could go back all the way to Aristarchus of Samos (c.310–c.230 BCE) but although he and his heliocentric theories were revived in the Early Modern Period, it was largely with hindsight and he played no real role in the emergence of heliocentricity in that time. However, we should definitely give a nod to Martianus Capella (fl.c. 410–420), whose cosmos model with Mercury and Venus orbiting the Sun in an otherwise geocentric model was very widespread and very popular in the Middle Ages and who was quoted positively by Copernicus.

Another nod goes to Jean Buridan (c.1300–c.1358/61), Nicole Oresme (c.1320-1325–1382), Pierre d’Ailly (1351–1420) and Nicholas of Cusa (1401–1464) all of whom were well-known medieval scholars, who discussed the model of geocentrism with diurnal rotation, a model that was an important step towards the acceptance of heliocentricity.

I start with a figure, who most would probably not have on the radar in this context, Jacopo d’Angelo (c.1360–1411). He produced the first Latin translation of Ptolemaeus’ *Geōgraphikḕ Hyphḗgēsis*(*Geographia*or *Cosmographia*) in Florence in 1406.

This introduced a new concept of cartography into Europe based on a longitude and latitude grid, the determination of which requires accurate astronomical data. Mathematical, astronomy based cartography was one of the major forces driving the reform or renewal of astronomy in the Early Modern Period. Another major force was astrology, in particular astro-medicine or as it was known iatromathematics, which was in this period the mainstream school medicine in Europe. Several of the astronomy reformers, most notably Regiomontanus and Tycho, explicitly stated that a reform of astronomy was necessary in order to improve astrological prognostications. A third major driving force was navigation. The Early Modern Period includes the so call great age of discovery, which like mathematical cartography was astronomy based. Slightly more nebulous and indirect were new forms of warfare, another driving force for better cartography as well as the collapse of the feudal system leading to new forms of land owner ship, which required better surveying methods, also mathematical, astronomy based. As I pointed out in an earlier post the people working in these diverse fields were very often one and the same person the Renaissance mathematicus, who was an astrologer, astronomer, cartographer, surveyor or even physician.

Our next significant figure is Paolo dal Pozzo Toscanelli (1397–1482), like Jacopo d’Angelo from Florence, a physician, astrologer, astronomer, mathematician and cosmographer.

Most famous for his so-called Columbus world map, which confirmed Columbus’ erroneous theory of the size of the globe. In our context Toscanelli is more important for his observation of comets. He was the first astronomer in the Early Modern Period to treat comets as astronomical, supralunar objects and try to record and measure their trajectories. This was contrary to the ruling opinion of the time inherited from Aristotle that comets were sublunar, meteorological phenomena. Toscanelli did not publish his observations but he was an active member of a circle of mathematically inclined scholars that included Nicholas of Cusa, Giovanni Bianchini (1410 – c.1469), Leone Battista Alberti (1404 – 1472),Fillipo Brunelleschi (1377 – 1446) and most importantly a young Georg Peuerbach (1423–1461) with whom he probably discussed his ideas.

Here it is perhaps important to note that the mathematical practitioners in the Early Modern Period did not live and work in isolation but were extensively networked, often far beyond regional or national boundaries. They communicated extensively with each other, sometimes in person, but most often by letter. They read each other’s works, both published and unpublished, quoted and plagiarised each other. The spread of mathematical knowledge in this period was widespread and often surprisingly rapid.

We now turn from Northern Italy to Vienna and its university. Founded in 1365, in 1384 it came under the influence of Heinrich von Langenstein (1325–1397), a leading scholar expelled from the Sorbonne in Paris, who introduced the study of astronomy to the university, not necessarily normal at the time.

Heinrich was followed by Johannes von Gmunden (c.1380–1442) who firmly established the study of astronomy and is regarded as the founder of the 1^{st}Viennese School of Mathematics.

Georg Peuerbach the next member of the school continued the tradition of astronomical studies established by Heinrich and Gmunden together with his most famous student Johannes Regiomontanus.

It can’t be a coincidence that Peuerbach and Regiomontanus extended Toscanneli’s work on comets, with Regiomontanus even writing a pamphlet on the determination of parallax of a moving comet, which was only publish posthumously in the sixteenth century. The two Viennese astronomers also designed and constructed improved astronomical instruments, modernised the trigonometry necessary for astronomical calculations and most importantly with Peuerbach’s *Theoricarum novarum planetarum*(*New Planetary Theory*),

first published by Regiomontanus in Nürnberg in 1472, and their joint *Epytoma in almagesti Ptolemei*, a modernised, shortened improved edition of Ptolemaeus’ *Syntaxis Mathematiké*

first published by Ratdolt in Venice in 1496, produced the standard astronomy textbooks for the period right up into the seventeenth century.

The work on the Viennese School very much laid the foundations for the evolution of the modern astronomy and was one of the processes anchoring the ‘modern’ study of astronomy an the European universities, How the journey continues will be told in Part II of this series.