For our first public lecture of 2024, Prof Paul Callanan told us about the astronomy of the medieval Irish monks, a topic that interests him and he has researched. Paul is Professor of Physics and Astronomy, UCC, and an honorary life member of Cork Astronomy Club. Main picture shows Prof Callanan at UCC’s Crawford Observatory. Below, Skellig Islands, home to an isolated medieval monastery.
Highlights from Paul’s talk: Due to the slow precession of the axis about which the Earth rotates, the constellations observed by the monks from Skellig Michael (inhabited from the 6th to the 12th centuries) would have been shifted in the sky relative to what we see today. For example since 600 AD Polaris, the “North Star”, has shifted by about 16 full moons width.
At this time the understanding of the cosmos placed the Earth firmly at its centre: the Moon, Sun, planets and stars were located on spheres and moving in circles, following the model perfected by Ptolemy in the second century.
Illustration: above, the Ptolemaic universe, below, John Scottus Eriugena on a pre-Euro Irish banknote
“At the furthest ends of the earth”
Irish monks played a key role in a major controversy of the time – how to calculate the date of Easter, a calculation called the ‘Computus’, to determine the first Sunday after the first full Moon after the Spring Equinox. The Irish monk’ views didn’t please Pope Honorius I who around 629 AD admonished them “not to think that their small number, at the furthest ends of the earth, were wiser than all the ancient and modern churches of Christ through-out the world”.
John Scottus Eriugena (c.800-877), ‘John the Irishman’ was one of the greatest intellectuals of the Medieval Age. His writings have been interpreted as suggesting that Mars and Jupiter orbit the Sun (with the Sun orbiting the Earth).
In the Irish Annals, monks recorded solar and lunar eclipses and aurorae, the apparition of Halley’s comet in 1066, and possibly the ‘new star’ that appeared in 1054 AD, the origin of the Crab Nebula.