Autumn equinox 2026: When is it and what happens?

Autumn equinox 2026: When is it and what happens? By Elizabeth Rizzini Lead Weather Presenter 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 the precise moment when the Sun crosses the celestial equator and neither hemisphere is tilted toward or away from the Sun, meaning day and night are nearly equal in length across the globe. And although the equinox itself cannot be seen, the date holds cultural and spiritual significance for some people. Gatherings take place at sites including Stonehenge, where people come together to mark the occasion and watch the Sun rise.

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What is the difference between the equinox and equilux?

The term "equinox" comes from Latin and means equal night. At the equinox, day length is measured from the moment the centre of the Sun is on the horizon, giving 12 hours from sunrise to sunset and 12 hours from sunset to sunrise. However, it is the upper limb of the Sun that is first visible at sunrise and last visible at sunset. Because of atmospheric refraction — sunlight being bent by the atmosphere — there is still light for a period when the Sun is not directly visible. This adds extra time to daylight hours. In autumn, this means the moment when day and night are truly equal occurs after the equinox. This is known as the "equilux," which means equal light. This year, that occurs in the UK on Friday 25 or Saturday 26 September, depending on latitude.

Where in the UK are days getting shorter fastest?

Although the equinox occurs at the same instant everywhere, the change in daylight hours is not uniform across the UK. The farther north you go, the greater the difference between the long summer days and the short