Weather Station

Precession and Tilt

What it does

These experiments show how precession and axial tilt affect the Earth.

What you need

Modeling clay
A round toothpick
A pencil
A flashlight

What to do

Part 1

Make a marble-sized ball out of modeling clay.
Insert the toothpick through the middle of the ball until about a quarter-inch sticks through the other side.
Spin the toothpick on its smaller end like a top.
Watch how the ball of clay wobbles as it spins.

Part 2

Make an apple-sized ball out of modeling clay.
Insert the pencil through the center of the clay so that it sticks out on both ends.
With the toothpick, mark a line around the clay ball halfway between the top and bottom. This is your "equator."
Set the ball on a table so that the top of the pencil is tilted slightly toward the right.
Darken the room.
Holding the flashlight about 6 inches away from the ball, shine it on the left side of your model planet.
Observe where the light shines on the ball.
Repeat steps 6 and 7 with the flashlight shining from the right side.

What it's all about

In Part 1, the toothpick represented Earth's axis. As the spinning toothpick started to tilt, the clay ball began to wobble. The Earth also spins on a tilted axis, and it wobbles just like the clay model. This wobbling is called precession.

Part 2 shows how the Earth's tilt affects the seasons. The flashlight represents the sun. When the top half of the Earth is tilted away from the sun, it receives less sunlight than the bottom half. Therefore, it is wintertime in the Northern Hemisphere while it is summer in the Southern Hemisphere.

When the top half of the Earth is tilted towards the sun, the Northern Hemisphere gets a summer season. What season will it be in the Southern Hemisphere?

Remember, be sure you have a parent, teacher, or other adult help you!