AUTUMN is upon us and before long leaves will start falling from trees as cold weather sets in.
As we get ready for conkers and pumpkins, here’s when the seasons officially change, when the autumn equinox will take place and why it’s still summer according to astronomers.
When does summer officially end and autumn start?
There are two different dates that mark the end of summer and the beginning of autumn.
This depends on whether you are referring to astronomical or meteorological autumn.
For meteorologists, summer comes to an end on August 31 and autumn begins on September 1, running until Thursday, November 30.
But astronomers say summer ends on September 22 in the northern hemisphere and autumn begins on Monday, September 23.
Who decides the date for autumn 2019, and how?
Both astronomers and meteorologists use different methods in deciding when the seasons change.
For meteorologists, they use the Gregorian calendar to split the year into four equal periods to help them with weather forecasting.
This means they define autumn as taking place in September, October and November – so for them, autumn begins on September 1 and runs until November 30.
But astronomers base their seasons on celestial events, and for autumn, the date is decided when the hours of daylight and darkness are roughly the same, known as the equinox.
This usually occurs around September 21-24 in the northern hemisphere, and astronomers believe the first day of autumn lies within this region.
There is also a third way of determining when autumn starts that is used by people who study phenology – plant and animal life cycles.
They look to changes in the natural world to determine seasons changing such as leaves changing colours and autumn fruits ripening.
But this relies more on weather, so the date for this can be open and change vastly each year.
Meteorological calendar of the seasons
- Spring: March, April, May
- Summer: June, July, August
- Autumn: September, October, November
- Winter: December, January, February
When will the autumnal equinox happen and what is it?
This year the autumn equinox in the northern hemisphere will take place on September 23 – the same day as the beginning of astronomical autumn.
The autumn equinox marks the day when the northern hemisphere slightly tilts away from the sun, meaning days become shorter and the temperature begins to cool.
Latest weather news
It is the day when daylight hours and night-times are of equal length.
This carries on until the winter solstice when the northern hemisphere begins to tip back towards the sun on its axis.
The end of autumn officially falls on December 21.
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