Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter, usually in late March or late September when the arrival of night becomes noticeably earlier. In theory, astronomically, the equinoxes ought to be the middle of the respective seasons, but temperature lag means that seasons appear later than dates calculated from a purely astronomical perspective. The actual lag varies with region, so some cultures regard the autumnal equinox as "mid-autumn" whilst others treat it as the start of autumn.Did you ever wonder how and why a fall leaf changes color? Why a maple leaf turns bright red? Where do the yellows and oranges come from?
During winter, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in the summer, because they are covered up by the green chlorophyll.
In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.
Many changes occur in the leaves of deciduous trees before they finally fall from the branch. The leaf has actually been preparing for autumn since it started to grow in the spring. At the base of each leaf is a special layer of cells called the "abscission" or separation layer. All summer, small tubes which pass through this layer carry water into the leaf, and food back to the tree. In the fall, the cells of the abscission layer begin to swell and form a cork-like material, reducing and finally cutting off flow between leaf and tree. Glucose and waste products are trapped in the leaf. Without fresh water to renew it, chlorophyll begins to disappear.
As the bottom cells in the separation layer form a seal between leaf and tree, the cells in the top of the separation layer begin to disintegrate. They form a tear-line, and eventually the leaf is blown away or simply falls from the tree.
The below song is perforemed by Justin Hayward, singing the Moody Blues "Forever Autumn."
The summer sun is fading as the year grows old,
and darker days are drawing near,
the winter winds will be much colder,
now you're not here.
I watch the birds fly south across the autumn sky
and one by one they disappear
I wish that I was flying with them,
now you're not here
like the sun through the trees you came to love me
like a leaf on a breeze you blew away
through autumn's golden gown we used to kick our way
you always loved this time of year
loose fallen leaves lie undisturbed now
cos you're not here x 3
like the sun through the trees you came to love me
like a leaf on a breeze you blew away
a gentle rain falls softly on my weary eyes
as if to hide a lonely tear
my life will be forever autumn
cos you're not here x 6
