Monday, September 22 marks the first day of Autumn.
We officially say, 'goodbye' to summer as the days become even shorter and the temperatures begin to drop.
The autumnal equinox (which happens at 11:44 a.m. EDT) is the point where the sun appears to cross the celestial equator, from north to south. It is told that on the day of the equinox, the sun rises exactly in the east and sets directly in the west.
While the word 'equinox' means equal night, it's not necessarily true on the exact date of the autumnal equinox. The precise day when the sun rises and sets at the exact same time varies across the country. Here in Michigan, September 25 marks the day when the sun will rise at 7:23 a.m. and will set at 7:23 p.m. providing exactly twelve hours of daylight.
Why Leaves Change Color in Autumn
Tree and plant leaves contain pigments that give them their color. Three pigments are involved in fall color:
Chlorophyll — gives leaves their green color.
Carotenoids — provide the yellow, orange, and brown colors
Anthocyanins — give the red and purple colors. In contrast to the other two pigments, anthocyanins are produced in the autumn, in response to bright light and excess plant sugars in the leaf cells.
During the growing season, most tree leaves are green because they are full of chlorophyll. Plants use chlorophyll to capture sunlight for photosynthesis, the process that enables them to manufacture their own food. The amount of chlorophyll is so high during the summer that the green color masks all other pigments present in the leaf. As the days grow shorter in the fall, chlorophyll production slows down and eventually stops. The carotenoids and anthocyanins that are present in the leaf then become visible.
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