Computational Methods

Claire Hall and Liam Shaw (Oxford)

We have been working on the internal consistency of predictions of planetary influence in Vettius Valens; we use an interdisciplinary methodology which uses statistical and computational methods to analyse Valens' descriptions of the influences of the combinations of planets. We're interested in the contrast between how scholars talk about Ptolemy's astrological system (usually described as very theoretical) and Valens' work (usually described as practical, disorganised, mechanical etc). In contrast, we argue that there is a high level of internal consistency in the way Valens conceives of planetary influences, and while he doesn't follow a strictly Aristotelian physical theory like Ptolemy does, there is nevertheless a degree of conceptual abstraction in his understanding of the combination of astrological influences.

Our work has a bearing on wider questions including theories of prediction among astrological practitioners, understandings of the physical and mythological characteristics of the planets, and methodologies for studying ancient astrology (particularly the use of statistical methods). We'd be very happy to be put in conversation with those working on astrology from a different area / time period.

Vanishri Bhat (Independent Researcher)

Eclipses: Astrological Predictions to Astronomical Calculations in Indian Astronomy

The phenomenon of eclipses has been widely differently interpreted by different traditions, depending upon their own social and cultural background. Being bewildered by the darkness, people of the Vedic culture seem to have prayed Indra, the head of Gods to drive away the demon and rescue them from the illusions created by him. In fact, different traditions in the ancient times viewed the phenomenon of eclipses in quite different ways. For instance, Chinese thought that during a solar eclipse, the sun was being swallowed by a huge dragon. While the Greeks thought that eclipses were indicative of ill omens, in the Indian puranic literature the two nodes of the moon's orbit namely  Rahu and Ketu have been personified as demons swallowing the sun and the moon during an eclipse. Different predictions based on horoscopes due to eclipses can be found in Indian Palita Jyotisha.

Though references to eclipses can be found even in the Vedic literature, a systematic procedure for their computation are to be found only in the texts composed much later. The text Aryabhatiya composed in 499 AD, besides succinctly describing what an eclipse is, also presents algorithms for the computation of solar and lunar eclipses. During my presentation, besides presenting an overview of the eclipses and predictions as seen by the ancients , I will also highlight the algorithm given in Indian astronomical texts for the calculation of eclipses.