To Everything There Is a Season

Spring is here, and everything that goes with it. The days are getting longer, the sunshine is getting stronger, and plants are growing and flowering like crazy. But why do we have spring? Or summer, fall, or winter? Why do we have seasons?

It's because of the Earth's tilt on its axis. Think about a globe. You know how it's mounted at an angle, so a line drawn between the north and south poles doesn't go straight up and down? Globes tilt like that because the Earth tilts like that. And as our planet goes around the sun once each year, that tilt means we get more hours of sunlight in the summer and fewer in the winter. Not only that: That sunlight is stronger during summer, when the sun is overhead, than in winter, when it's closer to the horizon. So we end up with both more light and more heat during the summer months.

Plants and animals respond to these natural phenomena. Plants "know" that there'll be more sunlight, warmer weather, and, in many places, more rain, so that's when their seeds sprout. Animals realize there's going to be abundant food ahead, and start their families in the spring.

Another result of our planet's tilt is that the Northern and Southern Hemispheres have their seasons reversed. For instance, while it's spring for us, it's autumn in Australia and most of South America.