The slow retreat of summer light
As August gives way to September, the length of the day in Ireland shortens steadily, bringing earlier sunsets and longer nights. The shift becomes most noticeable in the weeks around the autumn equinox in September, when daylight and darkness are almost equal across the globe.
In Dublin on 31 August the sun will set at 8.18pm, giving the city about thirteen hours and forty five minutes of daylight. By 30 September the sunset comes at 6.42pm, cutting daily light to roughly eleven hours and forty two minutes. Another month later, on 31 October, the sun will set at 4.54pm, leaving less than ten hours between sunrise and sunset. Over these two months Dublin loses almost four hours of daylight.
The reason for this rapid shift lies in the tilt of the Earth’s axis. The planet is tilted at about twenty three and a half degrees, which causes different parts of the Earth to receive varying amounts of sunlight throughout the year. During summer the northern hemisphere tilts towards the Sun, giving Ireland long days and short nights. As the Earth continues its orbit, the northern hemisphere gradually tilts away from the Sun, reducing the hours of direct sunlight each day.
The autumn equinox, which falls this year on 22 September, marks the point when day and night are almost the same length. From then on, darkness begins to dominate, with each day a little shorter than the last. In September Dublin loses on average just over four minutes of daylight every day. By October the rate of loss slows slightly but still amounts to nearly two hours across the month.
The change is not always obvious from one day to the next, but by late October the earlier onset of dusk is impossible to ignore. What were once bright evenings in late August become late afternoon twilights by Halloween. The shifting balance of light and dark is one of the clearest signals of the seasons turning, guiding the calendar of daily life in Ireland for centuries.
