Our Science and Theirs

Gonzalo L. Recio (Quilmes)

I would like to contribute with a paper on Ptolemy's model for Mercury in the Almagest. It is widely held that the Almagest’s planetary models are the result of Ptolemy’s investigation of the motion of Mars. Indeed, this planet’s highly irregular retrogradations were the most difficult problem Greek astronomers faced, and it remained so until Kepler’s revolution in the 17th century. Given the smaller size of its orbit, its greater distance to us, and the relatively short periods during which it is visible, the problems raised by the motion of Mercury do not seem to have been the source of much innovation. However, in the Almagest Mercury is the only planet for which Ptolemy deviated from the basic model he had –presumably– devised from the research on Mars’, making it somewhat more complicated. The paper will show how the theoretical elements in the Almagest’s basic planetary models relate to our modern Keplerian understanding of planetary orbits, and how the peculiarities of Mercury’s model in book IX of Ptolemy’s work are the way he found to incorporate in his theory the observational consequences of Mercury’s unique feature: the great eccentricity of its orbit.

Luca Beisel (Berlin/Tel Aviv)

Modeling the Cosmos: Creating a Digital Humanities Research Environment for the History of Ancient Astronomy

In the ancient world, astronomers developed geometrical models to account for the motion of the celestial bodies. The earth in the center of the universe, they imagined the stars and planets to be located on rotating spheres around it, whose nested movement creates their individual paths in the sky.

The intricate designs of the pre-modern astronomical models from Eudoxos to Ptolemy prove difficult to grasp from their verbal descriptions and illustrations alone, but become very evident by means of digital modeling and visualization. With today’s technology, we have the possibility to represent ancient astronomy in the way it was originally conceived—as 'geometry in motion'.

I am developing a research software for the ancient history of astronomy. The aim of the project is to provide the Computational History of Astronomy with a novel platform to reconstruct astronomic models from the historical accounts, to enable researchers to interactively study and explore the options and constraints of the historic sources. Screenshots and a demo video on the project website: https://lucabeisel.de/ancient-astronomy/