In the Northern hemisphere (North America, the Northern part of South America, Europe, the northern two-thirds of Africa and most of Asia) Autumn usually begins on September 21st, 22nd or 23rd.
This Year (2021) Autumn begins on 22nd September and ends on the 21st December.
In Autumn you will notice that the leaves on the trees start to change colour but only on some trees. There are two types of trees: deciduous and evergreens. Deciduous tree leaves change colour but evergreens do not. The leaves change colour due to a lack of food. Leaves contain chlorophyll which make the leaves green. They also contain xanthophyll which make the leave look yellow and carotene which make the leaves look orange. During the spring and summer, the leaves look green because photosynthesis is occurring. Photosynthesis is the process on how the leaf gets food and water. The chlorophyll (green colour) gets light from the sun and water from the ground, turns it into food and stores it in the leaf. During the fall the days get shorted and the chlorophyll can not get enough light from the sun needed to make food. The leaves live off the stored food and start to lose chlorophyll and their green colour. When the chlorophyl leaves the leaf the yellow and orange colours start to show. When all the stored food is used up the leaf turns brown and falls from the tree.
Autumn is normally associated with dropping temperatures and the night’s drawing in as winter approaches. In the United Kingdom Autumn can often bring unsettled weather and towards the latter part of the season can often bring stormy conditions with strong gales due to Atlantic depressions moving over the UK.
Autumn and Wildlife
For much of the UK wildlife Autumn is a time for slowing down and preparation for the long winter ahead. Some animals Migrate, such as birds and butterflies, flying off to warmer places to live and find food for the winter. Some animals grow a warmer coat, such as Rabbits, to keep warm during winter. Some animals gather extra food, to stock up on food during the fall, such as squirrels, mice and beavers. At the end of Autumn large numbers of salmon fish can be seen navigating their way back down rivers to the water they were born in. This is known in the UK as The Great Atlantic Salmon Run.