You may have noticed the days getting shorter and the nights are drawing in, which only means one thing - autumn is officially here!

Today is the Autumn Equinox, marking the first day of autumn in the Northern Hemisphere.

An equinox occurs when the sun passes directly over the Earth's equator, resulting in a day and night that equal in length.

There are two equinoxes every year - the Spring Equinox which takes place around March 22, and the Autumn Equinox, which occurs around September 22.

In the southern hemisphere the seasons are flipped, and the September equinox marks the start of spring.

Here's everything you need to know about the autumn equinox 2020.

Autumn is finally here!

When is the autumn equinox?

This year, the autumnal equinox takes place on Tuesday, September 22.

From now on, the days will get shorter and the nights will get longer until the winter solstice on December 22, when the pattern will reverse.

Why does the equinox happen?

The equinox occurs because of the tilt of the Earth in relation to the sun. This is what causes the seasons.

During the summer time, the Northern hemisphere is tilted towards the sun. So we get longer days as more light falls on this part of the surface.

In the winter time it's the Southern hemisphere that gets the majority of the light.

Equinoxes occur when the axis of rotation of the Earth is exactly parallel to the direction of motion of the Earth around the sun.

This means that day and night length is exactly 12 hours at all points on the Earth's surface.

Equal night

The word equinox is Latin for "equal night".

Meteorologists use it as the official turning point in the seasons because, although it can vary from year to year, it allows for the most accurate record-keeping.

It is celebrated around the world - notably at the Aztec monument Chichen Itza in Mexico.

During the equinox a sliver of light makes its way down the monument at sunset, drawing in crowds of onlookers.

When do the clocks change?

The autumnal equinox should not be confused with the day the clocks change, which also happens around this time of year.

In the UK, the clocks will "fall back" one hour on October 25.