Autumn Equinox 2026: When is it and What Happens?
By Elizabeth Rizzini, Lead Weather Presenter
Updated 27 minutes ago (20 September 2026)
Astronomical autumn begins this week, with the autumn equinox taking place in the early hours of Wednesday. The equinox will occur at 01:06 BST on 23 September, according to Royal Museums Greenwich.
It is a precise moment in time when the Sun crosses the celestial equator, resulting in roughly equal day and night lengths across the world. Although the equinox itself cannot be seen, it holds cultural and spiritual significance for some people, with gatherings at sites like Stonehenge to mark the occasion and watch the Sun rise.
Equinox vs. Equilux
The word "equinox" comes from Latin, meaning equal night. At the equinox, daylight is measured from the moment the center of the Sun reaches the horizon, resulting in 12 hours of sunrise to sunset and 12 hours of sunset to sunrise. However, because of light refraction—light bending due to the atmosphere—there's still light for a brief period after the Sun is no longer directly visible, adding extra daylight hours.
In autumn, this means that the actual equal day and night occurs after the equinox, known as the "equilux." This year, that happens in the UK on either Friday 25 or Saturday 26 September, depending on your latitude.
Daylight Change Across the UK
Although the equinox is a global event, the change in daylight hours varies across the UK. The further north you go, the more pronounced the difference between summer's long days and winter's short days. Northern Scotland, for instance, experiences faster reductions in daylight than southern England around this time of year.
Will the Equinox Bring Colder Weather?
The autumn equinox marks the beginning of astronomical autumn but doesn't necessarily signal an immediate change in weather. As the Sun dips lower in the sky and days shorten, temperatures generally decrease. So far this September, UK mean temperatures have been above average overall, according to the Met Office. This week will see warmer conditions, particularly in the south-east of England, followed by rain on Wednesday and cooler air on Thursday.
Towards late September, weather is expected to become changeable, with slightly above-average temperatures but potentially clearer, colder nights bringing fog and even frost in some areas.