Autumn Countdown 2026

Autumn 2026 begins at the September equinox, usually on 22 or 23 September. The countdown above targets the exact astronomical instant, when the Sun crosses the celestial equator on its way south.

Daylight disappears fastest right now. Contrary to a common impression, light is not lost most quickly in December but around the equinoxes: at mid-latitudes we lose close to four minutes of daylight every day at this point. At the solstices the daily change is almost nil.

Why leaves change colour. The tree stops producing chlorophyll, the green pigment that masked everything else. The yellow and orange carotenoids were already in the leaf all year: they simply appear once the green withdraws. The reds are different — anthocyanins, manufactured late, at the very moment the leaf is emptying its reserves.

The clocks go back shortly afterwards: the last Sunday of October in Europe, the first Sunday of November in the United States and Canada. The two continents therefore spend a week out of their usual time difference.

Two autumns coexist: meteorologists start theirs on 1 September. This countdown tracks the astronomical one.