The tilt of the earth and the seasons
Objectives: Students use measurements and subtraction to prove change over time. Students describe why the seasons change. The shadows will grow in length between September and December. They will shrink in length between January and May.
Materials:
Procedure:
Take the class outside to a fixed landmark such as a picnic bench, a fence or swings. Record three things:
1. The date
2. The time of day
3. The length of the shadow
Keep probing the students to record and write of as many details as they can notice. Persuade the students to record as much as possible. Now have students measure their own shadow in teams. Have them write a simple sentence that contains the length of the shadow of their friend. Return to the classroom and ask the students to predict if they think the shadow will change in a few months. Use the discussion to model how to write a short prediction that they can copy.
IN APRIL OR MAY have the students find the page where they wrote their predictions and details. Go to the exact same spot and measure the same shadow at the same time of day. The shadow will be shorter in April than in January. The students then measure their own shadow with teams or partners and it too will be shorter.
Conclusion:
Shine a projector on the globe in your classroom. Put a dot on your home town and walk the globe slowly in a circle around the projector while a trusty student keeps the light on the globe. The dot is in direct light on one side of the circle and in less direct light on the other. The seasons are NOT caused by the distance from the sun to the earth. In fact the earth is closest to the sun in December than at any other time of the year here in the Northern Hemisphere. The tilt (23 1/2 degrees) both changes the number of daylight hours and the heating power of sunlight. The tilt of the earth changes the seasons .
Enrichment :
Show the students an activity that they can try for themselves in centers. Use a solar calculator and cover the panel with your finger to prove that the light is powering it. Next find a distance from the light source so that the calculator displays numbers but with some weakness. Then rotate the calculator to tilt the angle of light and the numbers will disappear. Again, a 90 degree angle will maximize light's power onto a surface and a low angle tilt will diminish it.
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