Reasons for Seasons
Modeling the Seasons
Creating the Earth-Sun System in the Classroom

 Time 1 period Materials lamp, globe, masking tape Teacher Background Standards Photo: Science for Ohio

Overview: Students explore a model of the earth’s daily rotation and its annual revolution around the sun. They try to figure out at which point each season occurs in their part of the world. This lays the groundwork for understanding the reasons for seasons and for making sense of Mystery Class clues.

Preparation: Prepare a simulation of the Earth-Sun system by placing a lamp on the floor to represent the sun. Use a globe to represent the earth. It will spin (rotate) on its axis and revolve around the sun. Cut a star shape out of paper, label it the North Star, and place it on the board. Orient the North Pole of the globe so it points toward the star. Finally, place 4 Xs of masking tape on the floor on each side of the lamp.

Laying the Groundwork
Ask a student to find your city or state on the globe and tape a small paper circle on it. Challenge them to keep an eye on this location – and the light it receives – as they explore how the Earth and sun interact!

Exploration
1. Discuss the terms rotation and revolution. Have a volunteer demonstrate rotation with his or her body and then with the globe. (You might reveal that spinning is another word for rotation.) Next, let them know that the Earth rotates counterclockwise on its axis. Have a volunteer demonstrate this. Ask students to notice what happens to the light hitting your globe's school location. Ask, What do you think each rotation represents? Explain your thinking. (Each represents a 24-hour day during which every location has daylight and nighttime.)

2. Ask another volunteer to show how the Earth moves (revolves) around the sun (also counterclockwise). Explain that the Xs represent different seasons and that the Earth is not up and down on its axis, but always tilted (23.5 degrees) with the North Pole facing the North Star at all times. As the student walks around the sun slowly to represent the earth’s revolution, remind him or her to spin the globe quickly to also represent days passing. Ask, What do you think one complete revolution represents? (A year or 365 ¼ days.)

3. Invite a volunteer to stand at one of the Xs and rotate the earth to show two days coming and going. Have another student take the globe and move counterclockwise to the next X and do the same, and so on with each season. Remind them to keep the North Pole pointing to the North Star as they revolve around the sun from season to season. As they do so, ask students to pay close attention to the sun's relationship to their hometown during each season.
Making Connections
• Challenge small groups to discuss which X they think is which season. You might prompt them to focus on their hometown and discuss characteristics of each season there: temperature, sunlight, and so on. They may want to again examine the relationship between their hometown circle and the lamplight on the globe. Also share this clue with them: the first days of spring and fall are called the equinox, which is related to the word equal.

• Have each group write a label for each of the four seasons and place the labels face down on what they think is the appropriate X. Then season by season, turn over the labels and ask each group to explain its thinking. Conflicts in labels should spark fertile discussions! Rather than confirm answers at this point, you might want to conduct the next couple of activities and revisit students’ ideas at the end. Alternatively, you can pass out and discuss the Earth, Sun, and Seasons drawing.

Assessment
Older Students: Have students draw diagrams showing the relationship between the earth and the sun as it would be on the day they are doing this activity. Then have them sketch North and South America on their "earth" and place a small x in the approximate location of their hometown.
Younger Students: Give students this challenge question: One day, a boy in Massachusetts is going skiing with his family. What might a girl in Australia be doing?