In our last two seasons discussions (part 1, part 2) we dispelled some common misconceptions about why we experience seasons here on Earth. In this discussion, we will dispel the last misconception I presented and conclude our seasons discussion with an activity that you can do to help you better understand the seasons.
The last misconception, The Earth’s axis changes the direction of its orientation throughout the year, is easily dismissed with the help of Sir Isaac Newton. Isaac Newton’s first law of motion states that an object in motion will keep doing whatever it’s doing until disturbed by some force. Because the forces acting on Earth are VERY small, the axis continually points toward Polaris throughout the entire year.
We have learned that the seasons are caused by the fact that Earth is tilted on its axis as it orbits the sun. In the summer, this makes the sun quite high in our sky, which keeps the sun’s energy concentrated, warming the ground. In the winter, the tilt remains the same but since Earth has gone half way around in its orbit, the sun is now low in our sky, which means that the light is more spread out, providing less energy to each square foot of ground. The result is that we cool off as winter approaches.
Try holding a flashlight pointed straight down to make a spot of light on the floor. Observe the brightness of the spot and also note the shape of the spot. If you put a piece of paper on the floor, you can trace the size and shape of the spot on the paper.
Now change the angle of the light. Move the flashlight so that its beam hits the ground at an angle. Keep the light pointed at the same spot on the floor and at about the same distance. You should see some change in the light. This change can be marked on the same piece of paper as a comparison.
What changes did you see? Was there any change in the apparent brightness of the light? Was there any change in the shape of the spot of light?
Observe how the intensity and brightness change according to the angle of the flashlight.