Reasons for Seasons

A Schoolyard Investigation

 Time few periods over course of school year Materials outdoor fence post or other vertical object, sticks, stones or chalk, tape measure or yard sticks, data sheet (below) Standards Teacher Background

Overview: By measuring shadows from fall through spring, students discover that they are longer in the winter and summer, and shorter in the spring and fall. They begin to grasp that longer shadows mean that the our hemisphere is tipped toward or away from the sun. This lays the groundwork for understanding the reasons for seasons and making sense of Mystery Class photoperiod and longitude clues.

Preparation
Start this activity in September. Involve students in choosing an area in the schoolyard or playground that gets a lot of sunlight. Select a vertical object (e.g., stick, flagpole, fence post) that has a clear area to the north so students can easily measure shadows. (You may already have done this if you conducted the activity, Exploring Hourly Shadows and Sunlight.)

Laying the Groundwork

• What do you think happens to shadows outdoors over the course of a year?
• Are shadows in the winter about the same as they are in the summer? Explain.
• What have you noticed or experienced? What questions do you have about shadows and sunlight?
Exploration
1. Ask students to hypothesize how long their object’s shadow will be around the first day of fall (the equinox) and explain their thinking. They can write down the measurement or stand where they predict the end of the shadow will be and mark it with a stake.

2. On the fall equinox, have the class chart the date, time, and shadow length. Older students can also track sunrise and sunset times. Students can make their own data sheets or use this printable version above.

3.  Thinking Like Scientists Before students gather data, ask, How can we keep this investigation “fair” as we measure the shadow from season to season? If necessary, share one of the following examples to spark students’ thinking: measure at same time of day, use the same starting point (bottom of shadow of same object), use the same measuring tool.

4. After measuring shadows on the fall equinox, ask, How long do you think our object's shadow will be on the winter solstice, and why?

5. Repeat these steps on the winter solstice and spring equinox. Note: Because Daylight Savings Time (DST) has ended since the fall observation, winter solstice measurements should be taken one hour later.

Making Connections — Discussion and Journaling Questions

• What patterns did you notice?
• How would you explain them?
• What questions do you still have?

 Seasonal Shadows: What to Expect Students should discover that the shadow gets longer in the winter and shorter in the spring. If they took a measurement on the summer solstice, it would be even shorter. From there, it begins to lengthen again as we head toward fall. Explain that the sun’s rays are more direct in your location during the summer and more angled during the winter. They’ll have a chance to explore this later. (Read more background on the reason for seasons.)

Assessment

• Assess the degree and accuracy to which students are able to justify their explanations of the changes in shadows in relationship to the sun's seasonal position.
• Draw a tree and a sun on a reproducible response sheet. Write in several different months. Ask students to draw approximately where they think the tree's shadow will fall at each month indicated.

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