Wednesday, September 22, 2010

Autumnal Equinox

Today is the Autumnal Equinox, the day when the sun crosses the equator from north to south, officially bringing us longer nights and shorter days. On the equinox, as the name implies, the length of our day and night is nearly equal. The equinox marks the official first day of fall. The harvest moon, the full moon closest to the autumnal equinox, will be gracing the night skies tomorrow, September 23rd. Historically, the light from the full moon at this time of year gave farmers extra time in the fields to gather their harvest; crops such as corn, squash, pumpkins, and beans are ready for gathering.
As students of phenology, our Audubon Naturalist in the Schools classes have been observing the changes in the seasons during recent visits to the Center. In the mornings we have discovered the grass wet with dew. This is a result of colder night temperatures; cold air cannot hold as much moisture as warm air. As the temperature drops over night, the water condenses and is deposited on the ground as dew.
We have also observed the yellowing of the cottonwood leaves and the reddish hue that many of the local shrubs such as wood's rose and golden current have acquired. This change in leaf color is triggered by the shortening of the days. Chlorophyll gives leaves their green color in summer, and is essential for photosynthesis, the chemical reaction that enables plants to produce their own food using the energy of the sun to convert carbon dioxide and water into sugars. The chlorophyll masks other pigments that are also present in the leaves. As the length of the night increases in autumn, chlorophyll production slows down and then stops, and eventually all the chlorophyll is destroyed. This reveals the yellow, orange, and red pigments that paint the landscape in such beautiful hues during autumn.
Many changes are taking place in nature during this truly spectacular time of year. Animals are preparing for the colder months to come by caching (storing) food, putting on extra fat reserves, and by migrating away to warmer climes. We have heard numerous flocks of geese overhead during the past few weeks, and the students have observed that it is quieter in the woods lately; many bird species have already left for the south. Keep your eyes, ears, and nose tuned to nature, and share your phenological observations here.

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