Spinning on a Tilt

In science class, you have learned that Earth's axis of rotation is tilted at an angle of 23 ½° from perpendicular (straight up and down). This tilted axis explains why Earth has seasons. For example, when the Northern Hemisphere is tilted toward the Sun during the summer months, the sunlight hitting that part of Earth falls on a smaller area and is thus more intense. This factor, along with an increase in the number of daylight hours, produces warm summer temperatures. How can you be sure this is the reason? Try this activity with your family to find out!


A hand holding a flashlight pointed at a grid taped to a wall.


Ask an adult to help you tape the graph paper to the cardboard. Hold the cardboard perpendicular to the table surface. Have a family member shine the flashlight onto the graph paper from the side, about two feet away. Next, trace the outline of the flashlight beam on the graph paper. Count the squares on the graph paper that are enclosed or partially enclosed by the circle of light. Now tilt the cardboard at a 45 degree angle and repeat the steps. Trace the new outline of the beam with a different color. Count the squares. Try several other angles, marking the outlines with different colors.


Did the area of the light beam increase or decrease as you tilted the cardboard? How did you determine this? How do the results of your experiment help demonstrate the cause of the seasons?