Autumn is now in full swing, with crisp, chilly mornings and golden leaves floating to the ground.
But as the air gets cooler, our minds are already turning to the holiday season. So when exactly does winter officially start?
Here’s what you need to know.
When does winter start?
The start of winter is marked by two different dates - a meteorological and an astronomical date.
However, the Met Office explains that the day in our calendar that marks the first day of winter usually refers to the astronomical seasons.
However, meteorologically, the start of winter is defined by the seasons.
When is the meteorological start of winter?
By the meteorological calendar, the first day of winter is always 1 December and the season ends on 28 February (or 29 February during a Leap Year).
Meteorological seasons split the seasons into four periods, made up of three months each.
These seasons are divided to coincide with the Gregorian calendar, which makes it easier for meteorological observing and forecasting to compare seasonal and monthly statistics.
The seasons are defined as: spring (March, April, May), summer (June, July, August), autumn (September, October, November) and winter (December, January, February).
When is the astronomical start of winter?
The astronomical start of winter refers to the astronomical seasons, which are a result of the Earth's axis and orbit around the Sun.
The Met Office explains, “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.”
This year, astronomical winter will begin on 21 December 2020 and end on 20 March 2021.
For the next few years, the dates for astronomical winter will be:
Winter 2020: starts on Monday 21 December 2020, ends on Saturday 20 March 2021
Winter 2021: starts on Tuesday 21 December 2021, ends on Sunday 20 March 2022
Winter 2022: starts on Wednesday 21 December 2022, ends on Monday 20 March 2023
Winter 2023: starts on Friday 22 December 2023, ends on Wednesday 20 March 2024
Winter 2024: starts on Saturday 21 December 2024, ends on Thursday 20 March 2025
Both Equinoxes and Solstices are also related to the Earth's orbit around the Sun, but the dates of the Equinox and Solstice aren't fixed due to the Earth's elliptical orbit of the Sun.
This means that the Earth's orbit is not a perfect circle, it is elliptical, or slightly oval-shaped, and as a result there is one point in the orbit where Earth is closest to the Sun and another where Earth is farthest from the Sun.
What are the Equinox and Solstice?
Equinox and solstice are important parts of the astronomical calendar, which determine the transitions between the seasons.
The Equinox in the Northern Hemisphere occurs twice a year. The first of the year occurs around 20 March, which is the spring equinox, and then again around 22 September, which is the autumn equinox.
The Solstice also occurs twice a year, and is usually referred to as the 'summer solstice' and 'winter solstice'.
The summer solstice occurs around the 21 June in the Northern Hemisphere, and is the day of the year with the longest period of daylight.
However, the winter solstice usually occurs on or around the 21 December in the Northern Hemisphere, and is the day with the shortest period of daylight.
A version of this article originally appeared on our sister title, The Scotsman.