When is the first day of autumn 2023 and what is the autumn equinox?

12 September 2023, 11:59 | Updated: 12 September 2023, 12:31

Young girl holding up autumn leaf in the sunlight alongside a picture of pumpkins
Autumn is a favourite time of year for many Brits. Picture: Getty

By Zoe Adams

September's heatwave is officially over with many welcoming the cooler temperatures and the excitement of everything autumn has to offer - so when does autumn start in 2023?

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Summer in the UK has been described by many as disappointing and a washout, however, a last minute September heatwave has set everyone up nicely for the upcoming autumn.

With temperatures hitting above 30 degrees for over a week, many Brits have now found themselves welcoming the cooler climate after the days and night brought hotter temperatures than average for this time of year.

So as the weather changes, we officially begin to prepare for autumn and all the fun that it brings including warmer clothing, Halloween and cosy nights in watching TV and reading our favourite books.

So when is the official first day of autumn? And what exactly is the autumn equinox? Here's all the details you need.

A family having lots of fun and running in a park in autumn as leaves are on the floor
Autumn has two official start dates in the UK depending on what system you follow. Picture: Getty

When does autumn start in the UK?

Unfortunately, it's not just as easy as a date on a calendar to pinpoint the exact day autumn starts.

Instead, the official start date of autumn is determined by which system you follow - either the meteorological or the astronomical definition as both give different dates.

When is the meteorological autumn start date?

The simpler of the two systems, this method simply divides the calendar year into four, giving each season three full months.

It means every year, autumn begins on September 1st and lasts until the final date of November where winter officially starts.

Spring is from March to May, and summer is from June until August.

A forest full of red, brown and orange leaves as it welcomes autumn
Autumn brings cooler temperatures and darker evenings. Picture: Getty

When is the astronomical autumn start date?

Working out an official start date for the beginning of autumn becomes a little more complicated with this system as it relies on the position of the autumnal equinox.

This happens on a different date every year in September, with it being Saturday 23rd September in 2023.

The Met Office explains that: “The astronomical calendar determines the seasons due to the 23.5 degrees of tilt of the Earth’s rotational axis in relation to its orbit around the Sun.”

According to this system, winter begins on Winter Solstice on Friday 22nd December.

What is the autumnal equinox?

Equinoxes, which means 'equal night' in latin, are used to mark the first days of spring and autumn while solstices mark the first day of summer and winter.

The Met Office explained: "On the autumn equinox, day and night are of roughly equal length and the nights will become increasingly longer than the days until the spring equinox, when the pattern is reversed."

"It also marks the time of year when the northern hemisphere begins to tilt away from the Sun, resulting in less direct sunlight and consequently the cooling temperatures."