For many of us in the Northern Hemisphere, September marks an almost immediate shift from summer to autumn, whether the season has officially begun or not. 

Children are back or days away from a new school year, cosy autumnal favourites reappear on menus, wardrobes are reorganised for cooler weather and days feel suddenly shorter. 

What we don’t always register is that for most of us in the Northern Hemisphere, daylight hours have been slowly reducing since peaking during the summer solstice (21 June 2026). In London, days are already over three hours shorter, and by the winter solstice (21 December 2026) – the end of autumn – they’ll be less than half the length of the longest summer days. 

So why do we notice the change so acutely in September? Having already lost a chunk of daylight during August, September sees us start in a darker place. Additionally, daylight hours are generally decreasing at a faster rate, peaking around the autumn equinox, which falls on 23 September this year.

Ultimately, it’s probably a combination human mentality, commercial trends and nature doing its thing that propel us into autumn. But during these transitional periods, it’s pretty cool to sit back and think about the mysterious workings of our world.