Google has celebrated the first day of autumn with a Doodle on its home page.

The animation shows a black and white cartoon figure hop past five grey trees, transforming the leaves into rich autumnal colours.

With the character's final leap, the leaves fall from the trees – revealing the word ‘Google’ in gnarled branches. A large red leaf then floats down and lands on the smiling character’s head.

This year, the autumn equinox falls in the northern hemisphere on 23 September - the date where day and night are of equal lengths. The Latin term equinox, or ‘equal night’, is derived from this phenomenon.

The equinox occurs because the Earth’s axis tilts neither away nor towards the Sun.

Meanwhile in the southern hemisphere, the September equinox marks the beginning of spring. Therefore, at the South Pole residents will be celebrating the first appearance of the sun in six months, while those in the North Pole will be preparing for six months of darkness.

Druids celebrate the Autumn equinox on Primrose Hill, London. (Getty Images)

Early in the morning, Druids and Pagans will gather to mark the festival of Mabon - including at Stonehenge, where the sun will rise between the bolders.

Traditionally, Mabon is when livestock is slaughtered and preserved to provide enough food for the winter.

Video: Explaining the Autumn Equinox