Today is Saint Patrick’s Day, so let’s talk about Irish astronomy as it was practiced in the time of the Saint. In the fifth century the Irish made accurate observations, using stone circles that, like the famous Stonehenge of England, could predict sunrise and sunset positions and the beginnings of seasons. The Julian calendar of Rome was used in Ireland, and the Church relied on Irish astronomy to help establish the dates of Easter and other religious feasts, as witnessed by the Sixth century abbot, Mo-Sinu maccu Min of County Down. In the Seventh Century the monk Aibhistin suggested a connection between the tides and the phases of the moon. And then there are the Celtic constellations: Leo the lion which appears in the east after sunset, was An Corran, a sickle or reaping hook. The Irish saw Orion the Hunter as the hero Caomai, the Armed King. And the Milky Way was called Bealach na Bo Finne - the way of the white cow.