Curious Nature: Fall is now upon us
September 24, 2012
Did anyone else notice a change in the air around, say, 8:49 a.m. on Sept. 22? Was it a little crisper? Felt a little cooler? Maybe the sun’s angle suddenly seemed lower than it had all summer? For those of you with incredibly sharp senses, that moment was the beginning of autumn in the Rockies. Welcome to the new season!
Remember the first day, way back in mid-August, that felt fall-like? Suddenly, the sun was down earlier and there was a chill in the air around 7:30 p.m. We rely on certain external factors to alert us to the change of season. I personally think of fall as the time baseball season begins to wind down, football season starts to pick up and summer clothes go on sale. Nature has a more definitive way of changing seasons.
Beginning a new season at 8:49 a.m. may seem like an arbitrary time, but there is reason to it (doesn’t Mother Nature always have a method to the madness?) Picture the globe in your elementary school classroom. It tilted slightly to the right, to be exact, 23.4 degrees to the right. This simple tilt is what allows us to experience seasons.
As the Earth moves around the sun, it maintains this tilt. At our summer solstice, the northern hemisphere is pointed toward the sun. The southern hemisphere is tilted away. As the earth continues its orbit, it reaches a point where the axis is neither tilted toward nor away from the sun.
For one day, at one moment (in this case, 8:49 a.m. Mountain Standard Time), the sun’s rays directly hit the equator. The next day, due to the axis of our planet, the southern hemisphere will experience a slightly longer day and our day will be shorter. The revolution continues and before we know it, we will have reached the other end of the orbit, the northern hemisphere will be angled away from the sun. Winter solstice! And so it goes.
But let’s not get ahead of ourselves. There are some obvious signs of fall around town. Have you taken a look at the hillsides recently? Have you stumbled upon a bear munching berries? All these behaviors are dictated by the tilt of the Earth’s axis.
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Black bears, the only species of bear still found in Colorado, eat 90 percent vegetation and 10 percent carrion or meat. Their diet necessitates that they hibernate during winter when their main food source is scare. As we approach the equinox, it begins to get colder at night and even freeze. This affects what plants are out and thriving. The bears living in this area are genetically ingrained with this knowledge and know it’s time to head to their dens.
Let’s talk about the beautiful colors painting our hillsides. The aspen are at it. Their signal to change color is a shorter night. Chlorophyll, the molecule that makes leaves green, is continually produced in sunny, warm conditions. Once night reaches a certain length, the trees can’t produce enough chlorophyll to keep the leaves green – ta-da, the leaves begin to change.
Whether 8:49 a.m. felt a little special to you or not, you can get out and embrace fall in the valley. While you’re enjoying the fall colors, thank the Earth’s axis, with its magnificent tilt, for providing us with such wonderful scenery.