The official start of autumn varies depending on the calendar followed, with three distinct dates recognised in 2026.
According to the meteorological calendar, autumn begins on 1 September. This calendar is used by meteorologists like BBC NI weather presenter Barra Best to compare weather patterns and record climate data over decades. Gary Quinn, director of rivers operations within the Department for Infrastructure, also monitors this calendar for planning emergency responses to potential flooding, particularly after a dry summer.
In contrast, the ancient Celtic calendar marks 1 August as the start of autumn, a date celebrated by druids as Lúghnasadh, signifying the early harvest. Eimear Burke, Chosen Chief of the Order of Bards, Ovates and Druids, described it as a time for the first cutting of corn and wheat. Fiona Byrne, a history curator at the Ulster Folk Museum, noted the Celtic calendar's importance for ancient Celts in preparing for winter and harvesting crops.
For those following the astronomical calendar, autumn will not officially begin until 23 September. This calendar is based on the Earth's position relative to the sun, defined by solstices and equinoxes. Marc Sarzi, Head of Research at Armagh Observatory and Planetarium, explains that this calendar is based on a sidereal year, which is the time it takes for the Earth to orbit the sun.