With the days getting progressively shorter and the light fading earlier with every passing week, we know that autumn is upon us.
In fact, depending on which of two seasonal calendars you follow, autumn may have already begun.
The extreme heatwave the UK experienced just a few weeks ago now seems like a distance memory as people prepare to wrap up warm in blankets and get their big coats back out of the wardrobe.
We all know, of course, that in the UK the clocks are turned back every October to mark the end of British Summer Time.
But, the official start of autumn actually comes much sooner than this date.
So, when exactly does autumn start and what is the autumn equinox?
Here’s everything you need to know.
When does autumn begin?
There are actually two ways of calculating the first day of autumn, depending on whether you follow the meteorological or definitions of the seasons.
But, whichever one you follow, both are happening in September.
Meteorological autumn will begin first, beginning on Thursday 1 September, followed by astronomical autumn which will begin on Friday 23 September.
What’s the difference between meteorological autumn and astronomical autumn?
These are the key differences between meteorological autumn and astronomical autumn, and how the date of each is determined.
The meteorological autumn date is the easiest to work out.
It is based on the simple principle that the year is split into four seasons, and that each of these seasons are made up of three full months, as per the Gregorian calendar.
This definition makes it easier to compare seasonal and monthly statistics, and means that every season starts on the same date every year.
This means that every year autumn begins on 1 September and lasts until 30 November, with winter then starting on 1 December.
In this instance, summer ends of 31 August.
The astronomical season is less straightforward to work out as it can change every year.
This is because it starts on the date of the autumn solstice, also known as the autumn equinox or the September equinox, which comes later in September but can vary slightly from year on year.
In 2022, the autumn solstice falls on Friday 23 September, which is a year later than last year when it fell on Wednesday 22 September 2021.
In this instance, summer will end on Thursday 22 September.
It can, however, occur on any date between 21 and 24 of the month, although 22 September is the most common date for it to occur.
The astronomical autumn then lasts until another changeable date, the winter solstice, the shortest day of the year, which is set to take place on Wednesday 21 December this year.
The number of daylight hours on the shortest day will be 7 hours, 49 minutes and 42 seconds.
That’s 8 hours, 48 minutes and 38 seconds shorter than the summer solstice, when daylight hours are at a maximum.
What is the autumn equinox?
They happen twice a year, at the start of spring and autumn, and mark the moment the Earth’s equator passes directly through the centre of the sun’s path.
On each of these days, the planet should get 12 hours of daylight and 12 hours of darkness, although this is complicated somewhat by the Earth’s atmosphere and weather conditions affecting the way we see sunlight.
The autumn equinox can occur at any time between 21 and 24 September, and marks the start of autumn - if you follow the astrological definitions of the seasons.
This year, the autumnal equinox will occur on 23 September at 1:04am UK time.
When will autumn end?
There are also two ways of calculating the last day of autumn.
According to the metrological measure of the seasons, the last day of autumn this year will be Wednesday 30 November, with winter then starting on Thursday 1 December.
But, the astrological measure of the seasons states that the last day of autumn 2022 will be on Wednesday 21 December, followed by the first day of winter on Thursday 22 December.