Summer Scurries Before Fall

A sugar maple leaf transitions from summer to fall earlier this week. Bob King

Have we come this far again? Yes, we have. While the pandemic has made some of us feel stuck in time, the Earth hurries along its orbit like an eager dog on a walk. Yesterday, daylight still dominated night by just a hair. Today they're equal at 12 hours apiece. In the brief interim summer became fall. It happened officially at 8:30 a.m. CDT today (September 22).

Achieving this delicate balance took six full months, and it will only take a day to break it. Tomorrow, night will have a slight edge, and by November, we'll wonder where all the light went. Fewer hours of daylight mean less sunshine and that leads to falling temperatures and seasonal change. One of those changes occurs in tree leaves.

Chlorophyll, the pigment that gives leaves their green color, uses sunlight to convert carbon dioxide and water into energy and food. It takes a lot of energy to make chlorophyll so when daylight dwindles and temperatures drop, leaves stop building it. The molecule breaks down into smaller pieces but won't go wasted — the plant will reassemble the fragments into next season's chlorophyll when increasing daylight restarts the engines of photosynthesis.

With the green out of the way, yellow and orange pigments called carotenoids are unmasked. These and the anthocyanins, which the plant deliberately produces in the fall to protect the leaves from sunburn and being eaten, add pink, red and purple to the autumnal palette. On your autumn walks it's fun to realize that the beautiful colors we all enjoy are a byproduct of nature's practicality.

Ice crystals coat a weed during last week's first frost. Bob King

Other changes result from the surplus darkness including the hushing of crickets and katydids at night, frost instead of dew on the morning grass, the softening of the sun's rays, earlier sunsets and later sunrises, bird migration, animal hibernation, ice and the joy of not mowing the lawn for six months.

The changes define our lives in many ways. The pandemic has messed with my sense of time, but I'd be lost for good without the seasons. So bring on the darkness, bring on the cold, and keep the changes coming.

What causes the seasons? Some might tell you it's Earth's changing distance from the sun, closer in summer and farther in winter. But nothing could be further from the truth. The planet is actually about 3 million miles closer to the sun in January than in July. Seasonal change comes down to a simple tip of a hat, or in this case, the tip of an axis.

Sonoma State University

The planet's tilted axis combined with its yearly trip around the sun causes first one pole and then the other to tip toward and then away from the sun. When the North Pole bows sunward, the sun appears higher in the sky and we experience summer. When that same pole is oriented away from the sun it's winter.

The fall and spring equinoxes are balance points where neither pole "has the advantage." We're sideways to the sun at those locations in our orbit, and sunlight falls equally across the entire planet. Again we see how a practical matter — the 23.5° tilt of Earth's axis — leads to profound consequences. When you consider how rich and all-encompassing nature is, the better we know it, the more beauty we find.