Marveling at the skies: comets through the eyes of the Anglo-Saxons

This research was partly funded by the Royal Society APEX award. The idea was first presented in an exhibition at the Ulster Museum in Belfast and some of the early results were shown at the British Academy in London. The BBC made a video about our project for their Ideas series. Here it is:

Comets are conglomerates of the very primitive materials that surrounded the young Sun. Once the planets formed from those same materials, their large masses cleared the interplanetary region and drove comets out beyond Neptune.

Because they are very small and because they have been stored far from the hot Sun for their entire lifetimes, comets are unprocessed by gravitational compression or heat.  They are extremely well preserved relics of a fascinating yet mysterious time we would like to study in more detail: the birth of our solar system.

Some comets have their orbits gravitationally perturbed by Neptune or other stars and plunge into the inner regions of the solar system. As they approach the Sun, they heat up and begin to sublimate. A cloud of gas and dust known as coma forms around the comet nucleus. Gravity and solar radiation push the coma and give rise to the distinctive tails that define comets.

Around 1705, the English astronomer Edmond Halley noticed in written records of comet sightings that a particular comet seemed to return to the skies every 76 years or so. He computed the comet’s orbit and predicted its subsequent visit would occur in 1758. Halley’s prediction was confirmed and the comet named after him.

Our research project follows in the footsteps of Halley: by combining comet orbit computations and written records from the Anglo-Saxon Chronicles we hope to unravel the scientific knowledge of people in the Middle Ages and to test theories about the structure of our solar system.

Speaking ahead of the exhibition launch and about the research project, Dr Cesario said: “This research project renegotiates the meaning and importance of medieval science and demonstrates how medieval records of comets can help test the theory of the existence of the elusive ‘Planet Nine’. Looking at records of comets in Old English, Latin, Old Irish and Russian texts we aim to show that the early medieval people actually recorded genuine astronomical observations, reflecting their interest in cosmology and understanding of the heavens.

“The idea for this study came about from the strong desire to challenge the common assumption and perceived lack of scientific enquiry in the early Middle Ages, or commonly referred to as ‘Dark Ages’. This was the spark that ignited the intellectual collaboration between a medievalist and an astronomer.”

Marilina Cesario (left) and Pedro Lacerda
Dr Lacerda, commented: “It is fantastic to be able to use data which is about one thousand years old to investigate a current theory. To me, this is one of the most fascinating aspects of our project.

“Any strong indication that a ‘Planet Nine’ is required to fit the comet sightings recorded in the Middle Ages will be a unique result and will certainly have a remarkable impact on our understanding of the solar system.”

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