For those of you in the Northern Hemisphere who were lucky enough to have a summer this year (we didn’t have much of one here in Ireland), it’s time to say goodbye!
Today, the 22nd of September, is the first day of autumn, also known as the autumnal equinox.
The term “equinox” is derived from an astronomical event in which the sun transits directly over the Earth’s equator. Day and night are approximately equal length on equinoxes, which is how the days got their name — it means “equal night” in Latin.
From today, the days will start to shorten in the Northern Hemisphere as winter approaches.
A sure sign of the onset of autumn can be seen in the leaves of trees. During the spring and summer the leaves have served as factories where most of the foods necessary for the tree’s growth are manufactured. The process, known as photosynthesis; takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green colour. Along with the green pigment are yellow to orange pigments; carotenes and xanthophyll, however most of the year these colours are masked by great amounts of chlorophyll.
In autumn, because of the changes in daylight hours and changes in temperature the leaves stop photosynthesising and hence the chlorophyll breaks down. The green colour disappears, and the yellow and orange colours become visible. At the same time other chemical changes may occur, which form additional colours through the development of red anthocyanin pigments.
This combination of beautiful colours makes for some fantastic scenery, as in this picture of Poulakerry Castle on the banks of the River Suir, Co. Tipperary, Ireland.
-Jean
Photo courtesy of Joe Cashin
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