Google has marked the start of the autumn equinox with a new doodle of traditional harvest vegetables and a playful squirrel. Here are five things you may not know about the first day of autumn:

What does the term ‘equinox’ mean?

The word means 'equal night'. But daytime and night are not actually equal because although the centre of the sun sets 12 hours after it rises, the day begins when the upper edge of the sun reaches the horizon. Therefore days are still slightly longer.

Is the equinox always on the same day?

It usually falls on the 22 or 23 September but in 1931, it fell on 24 September. The Gregorian calendar does not always match up because the planet takes 365.25 days to orbit around the sun, meaning the equinox is sometimes delayed a day. The next time it will fall on 24 September will be in 2303.

In pictures: The autumn equinox in Richmond Park Show all 8 1 /8 In pictures: The autumn equinox in Richmond Park In pictures: The autumn equinox in Richmond Park London A cobweb catches the early morning mist in Richmond Park in London In pictures: The autumn equinox in Richmond Park London A fallow deer stag is seen in Richmond Park In pictures: The autumn equinox in Richmond Park London Deer are seen through the morning mist in Richmond Park In pictures: The autumn equinox in Richmond Park London Ducks and geese are seen through the morning mist on the lake at sunrise in Richmond Park In pictures: The autumn equinox in Richmond Park London Ferns glow in the morning light in Richmond Park In pictures: The autumn equinox in Richmond Park London A red deer is seen through the morning mist in Richmond Park In pictures: The autumn equinox in Richmond Park London The lake at Richmond Park is seen through the morning mist In pictures: The autumn equinox in Richmond Park London Trees are seen in the morning light in Richmond Park

So why do meteorologists say autumn begins on 1 September?

In order to make more accurate comparisons of seasonal weather from year to year, meteorologists often divide the seasons into four three-month periods.

What is the difference between the autumn equinox in the North and South Pole?

People living in the South Pole will be experiencing the first sighting of sunlight in six months, as the september equinox marks the first day of spring for them. But residents in the North Pole will be marking the beginning of six months of darkness.

How do people celebrate the autumn equinox?