Autumnal equinox signals the end of summer

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Happy fall, y’all! September 22 officially marks the beginning of the fall season, and all of the usual events that come with it including the loss of solar energy.

The suns strongest energy is focused directly at the equator today, and its primary focus will continue to head south as we get closer to the winter season as the sun angle declines.

We actually have a way of measuring the sun’s energy. We do that in BTUs (British Thermal Unit), the same unit of measurement you’ll see when shopping for a furnace or space heater.

During the height of summer, we can receive up to 1,800 BTUs here in the Quad Cities for the month of August. All of that energy is used for heating, evaporation and other physical processes. All of this occurs because the bulk of the suns energy is focused north of the equator.  This is a stark contrast to the measly 450 BTUs we typically receive during the month of December when we observe our shortest day of the year in terms of daylight. Most of our incoming solar radiation during the winter months is also reflected back into space thanks to the snow pack that typically sits on the ground.

This is the primary driving force behind why we have our different seasons here. Different amounts of incoming solar radiation over long periods of time drive weather patterns all across the world.

Meteorologist Andrew Stutzke

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