4-7 Lesson 4

Sunrise...Sunset - Bilingual Telemation Unit

4-7 Lesson 4:
What Causes the Seasons?

Background:

Earth's distance from the sun has little to do with the seasons. The seasons are caused by the tilt of the earth on its axis as it revolves around the sun. The earth is tilted at a 23.5 degree angle from a vertical axis drawn perpendicular to the plane of the earth's orbit around the sun. This tilt causes some parts of the earth to get slanting rays of sunlight some of the year and vertical rays of sunlight at other times.

Concepts:

When a hemisphere of the earth is tilted toward the sun, it is summer in that hemisphere. When it is tilted away from the sun, it is winter.

Objective:

Students will observe the effect on temperature of slanting and vertical light rays.
Students will use a model of the earth and sun to demonstrate how the tilt of the earth causes variations in the amount of light intensity different hemispheres receive during different seasons.

Materials:

For each team of four students:

2 thermometers
Black construction paper
2 flashlights
Protractor (optional)
Chalk (optional)

For whole class:

2 globes mounted so that the axis is tilted 23.5°ree; from vertical
Bright light source, i.e., a lamp with a 75 watt bulb

Pre-Assessment:

Ask students to write and draw their explanation for the changing seasons.

Sheltered Vocabulary:

The following vocabulary should be previewed, reinforced and reviewed for LEP students. Use posters, globes, diagrams and Total Physical Response to illustrate the vocabulary.

tilt, vertical, slanted, equator, orbit, hemisphere, axis, North/South Poles

Procedure:

Working in teams of four, students place each thermometer on black construction paper. Students should check the beginning temperature and record. Students should devise a table to record their data.
Two students hold the flashlights over the thermometers. One holds it so the light is hitting the bulb vertically, the other holds it so that the light is hitting the bulb at an angle approximately 23°ree;. (Protractors could be used to get more accurate angle measurements.)
After 5 minutes, students record temperatures and note any changes.
After letting the thermometers go back to room temperature, students can investigate the impact of different angles on the temperature.
If there's time students can outline the lighted areas of the black paper with chalk for the various angles.
After darkening the room, the teacher places the two globes on either side of the light source. On one globe, the USA should be tilted away from the sun, on the other it should be tilted towards the sun. Students observe and record differences in light intensity.
Walk one globe through an orbit around the sun. Keep the tilt oriented in the same direction. Record your observations. (NOTE: After an initial teacher demonstration, different students could do the orbit walk to reinforce the concept.)

Conclusion:

Are there differences in the temperatures for the vertical rays of light and the slanting rays? How do you account for the difference?
Which flashlight caused "winter"? Which caused "summer"?
Relate your investigations with the flashlight to your observations of the tilted globe. In what position does the USA receive slanted rays of light? What can you infer about its daily temperature at that time? What season do you think it is? In what position does the USA receive vertical rays of sunlight? What can you infer about its daily temperature at that time? What season is it?
How did the brightness of the light change on the USA when you walked the globe around the sun? Relate these changes to changing seasons.
When the USA had summer, what countries had winter?
Do all parts of the USA have the same seasons? Why or why not?
Was there any part or parts of the globe that had very little change in the amount of light it received? What part or parts? What could you infer about the seasons and climate in those parts of the earth?
When the USA is tilted towards the sun, what happens to the amount of sunlight when you travel from your city northward? When you travel southward?
[Students should have an opportunity to put it all together. Students should be able to answer the question "What causes the seasons?" relating the earth's tilt to the changes in the angle of sunlight resulting in changes in temperature.]

Assessment:

Choose from several assessment tools:

Students go back and revise and correct their initial pre-assessment answers.
In groups students draw a poster illustrating the causes of the seasons.
Students create a demonstration and explanation of the seasons for first graders. (NOTE: This could be a telecommunicated assessment if your class communicates with a lower grade as part of its telecommunication network).

Extensions:

Multicultural Enrichment:

Use the country of origin of your students as the basis for research on the activities, clothing and customs of different countries during the different seasons. If your class is not very diverse in origins have students choose countries that will show a broad range of cultures and seasonal change.

Language Arts:

Have students read the myths "Spring Defeats Winter" (Keepers of the Earth, by Michael Caduto and Joseph Bruchac) and "Persephone and Demeter" (D'Aulaires' Book of Greek Myths). Students can compare and contrast how the different cultures explained seasonal changes. Students can write their own myths.

Life Science:

Have students research the impact of seasonal variations on animal behavior. Behavior such as migration, nesting, hibernation, mating, and metamorphosis could be investigated. Also seed germination and temperature changes could be explored.

Technology:

How do the seasonal changes and climate impact energy uses and housing in different areas? What kinds of technology have made it easier to live in different seasons? Have students invent something that would make life easier during a season and in a location of their choice.

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