What Causes the Seasons?

Lesson by Jessica Allen, WEST Fellow

Objectives:
Understand that the tilt of the Earth causes the seasons.
The Earth’s tilt is 23.5 degrees.

Utah Core Curriculum Standards: 6th Grade - Science Standard II

Diagram from: http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Seasons.shtml

Introduction
1. Ask students: What causes seasons?
   All answers are acceptable.

2. Give a brief introduction to the Earth’s tilt and the angle of the Sun.
    Clear up any misconceptions (e.g. rotation causes the seasons, or the seasons are affected by the Earth’s distance from the Sun).
   Use an Earth-Sun-Moon model if available. If not, have a student represent the sun and use a globe to show the tilt and angle towards the Sun.

Activity 1: Understanding angle of incidence

Materials:
Yardsticks for every 2 students
Protractors

1.   Pair up students.

2.   Go outside and have them measure their partner’s height and their shadow height.

3.   Measure both partners.

4.   Record measurements in science notebook.

5.   Return to classroom.

6.   Make an appropriate scale so that both height and shadow will fit on a piece of paper.

7.   Have student draw a small to scale picture of their height and shadow.

8.   Connect the lines to make a triangle and measure the angle near their head.
This angle is the angle of incidence. This angle determines whether the Sun is directly hitting them or indirectly hitting them. 0 degrees is direct sunlight and their will be no shadow. The larger the angle the less direct the sunlight. The angle of incidence can be used to determine the season. A larger angle means more indirect sunlight and relatively colder air, a smaller angle means more direct sunlight and relatively warmer air. This angle changes daily and yearly. Do not let the students confuse angle of incidence with the angle of the tilt of the Earth.

9.   Have students compare their measured angles, they should all be the same.
       If there is some variation, explain that it is not because some students are taller but probably due to measurement error.

Activity 2: Understanding that the angle of incidence creates different temperatures.

Materials:
Yardstick
Flashlight
Solar Panel
Voltmeter

Beforehand:
1.   Attached voltmeter to solar panel to ensure that it works properly.

2.   Determine where experiment will happen (ideally in a dark room) and see if voltmeter is sensitive enough.

3.   Tape a flashlight to the end of a yardstick.

During Class:
1.   Tell the students that the class is going to test whether the angle of incidence changes the amount of energy or temperature that reaches a                given place on Earth.

2.   The solar panel represents your state and is absorbing the amount of energy that is reaching it.

3.   The voltmeter measures the amount of voltage (which represents energy or sunlight here) and we can record this amount.

4.   Set up a chart with the students as follows.

Angle	Voltage (Energy)	Season
0 degrees
45 degrees
90 degrees (etc., enter any angle you want)

5.   Have a volunteer hold a flashlight directly in front of the solar panel.

6.   Have a volunteer take the first measurement from the voltmeter.

7.   Move flashlight to a 45 degree angle.

8.   Take second measurement.

9.   Repeat with desired angles.

10. Have students graph the measurements.

11. Review why the voltage went down when the flashlight was moved up.

12. Fill in the season’s column and review what this has to do with the seasons.

13. Review concepts.
Example: You sunburn more quickly when there is more direct light (around noon) than when there is a higher angle of incidence (early morning or evening).

14. Have student measure their angles of incidence again in the afternoon and see how it has changed. You could also have them take the temperature when they measure their angles of incidence to demonstrate its relationship throughout the day.

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