Time until the first day of autumn

Astronomical autumn in the northern hemisphere begins at the September equinox, when the sun crosses back over the celestial equator heading south. The instant usually falls on 22 or 23 September, so this countdown uses 22 September as an approximation. Meteorological autumn starts on 1 September. The equinox is also when daylight starts shortening fastest at mid latitudes, which is why the change feels abrupt even though the date moves by barely a day between years.

Once the sun crosses back over the equator the nights draw in faster than at any other point in the year at mid latitudes, and the change is compounded a few weeks later when the clocks go back in Europe and North America. That makes the September equinox a useful reminder for anything depending on evening daylight: pitches need floodlights, commutes turn dark, and building work planned for the end of the day runs out of time. School terms are already under way by then across most of the northern hemisphere. Harvest festivals and the Chinese and Korean mid-autumn holidays are timed to the moon near this point rather than to the equinox itself. South of the equator the same instant starts spring, and the day lengths run the other way.

Ireland counts August, September and October as autumn, the quarter opening at Lughnasadh on 1 August, so the Irish season is nearly over by the time the equinox arrives. The United States treats the day after the early-September holiday weekend as the start, which sits closer to the meteorological line than to the astronomical one. Japan's traditional calendar marks risshu in early August, in the hottest part of the year, and the heat that follows it has a name of its own. Australia and South Africa both take 1 March, half a year from any of these.

The next one falls on Wednesday, 22 September 2027, and this page counts down to the midnight that starts it in whatever time zone your browser reports.

The harvest moon is the full moon nearest the September equinox, and its name comes from a piece of geometry. Around the equinox the moon's path meets the horizon at a shallow angle, so successive moonrises come only twenty or thirty minutes later each night instead of the usual fifty, which gave several consecutive evenings of useful light at the point in the year when a crop had to be got in. The effect is strongest at high latitudes and barely noticeable near the equator.

The harvest festivals attached to the same moon are older than any calendar definition of the season. The Chinese Mid-Autumn Festival and the Korean Chuseok both fall on the fifteenth day of the eighth lunar month, which puts them within a few days of the crossing, and Chuseok is the heaviest travel week of the Korean year. British harvest festivals are usually held on the Sunday nearest the harvest moon, a Victorian revival of a much older custom, and Sukkot in the Jewish calendar is another autumn harvest feast reckoned by the moon.