Talking about seasons with young children is a great way to engage students in the world around them. You probably talk with your students about the seasons throughout the school year. But do you know what causes the seasons? The changes between fall, winter, spring and summer can be explained by a relatively small phenomenon that has a large impact on our Earth.

We all know that the Earth is round —  but did you know that the Earth does not "sit-up" perfectly straight? It is actually tilted slightly — 23.5 degrees, to be exact. This is a small tilt, but makes a big difference!

It takes our Earth 365 days to revolve, or orbit, around the Sun. During some parts of the year, the top half of the Earth (where the National Air and Space Museum is located, in the northern hemisphere) is tilted away from the Sun, while the bottom half is tilted toward the sun. Six months later, the top half of the Earth is tilted toward the Sun, while the bottom half is tilted away from the Sun.  

Can you guess which season is which? When the northern hemisphere is tilted away from the Sun, it is winter there. Less sunlight is hitting the northern hemisphere, making the days shorter. At the same time, it is summer in the southern hemisphere.

Six months later, after the Earth travels halfway around the Sun, the top of the Earth is tilted toward the sun, making it summer there. More sunlight is hitting the northern hemisphere, making the days longer. At the same time, it is winter in the southern hemisphere.

The seasons depend on the angle of the Earth to the Sun - not how close the Earth is to the Sun! More concentrated sunlight shines on the part of the Earth tilted toward the Sun, and less concentrated light shines on the part of the Earth tilted away from the Sun.  

Try creating your own sundial with a flashlight. Notice how in the winter, the shadows are longer. This is because the Sun is lower in the sky. If you did this activity again in the summer, what do you think will happen with the shadows? Why? Check out Focused Exploration activities that you can do with your students to create your own sundial.