Reasons for Seasons
Exploring the Astronomy of the Seasons
Activity 4: Heating Up
Direct and Indirect Sunlight

(Activity #4 of Reasons for Seasons)

Overview: By conducting simulations, students explore the effects of direct and indirect sunlight on heating of the Earth.

Laying the Groundwork
If you conducted activity 1, ask, What did our shadow studies reveal about the angle of the sun at different times of year? What else do you think the angle of the sun affects as it hits the Earth’s surface?

Document students’ ideas and have them identify ones they can explore through direct observations or experiments. If they mention the Earth’s temperature, ask them to explain their thinking. Ask, How could we test this idea? Let students pursue their ideas, or suggest the following.

Part 1: 1 period; Part 2: 1 period

2 pie tins painted black, graph paper, flashlights

Exploration, Part 1
  1. Paint two pie tins black. Set both tins out in the sun. Ask, How could we simulate the sun's rays hitting one tin at an angle (indirectly)? They might, for instance, place one lying flat so that the sun shines directly on it and stand the other one up vertically in a piece of clay so it receives only angled rays.
  2. Ask students to predict which they think will absorb more heat and explain why they think so. After 10 minutes, have them feel both surfaces. If possible, place a thermometer in the face of each tin and measure the temperature difference.

Making Connections — Journaling and Discussion Questions

  • What differences did you notice?
  • How could you explain them?
  • How do your findings help you better understand the seasons?

Exploration, Part 2
Spark students’ thinking about why direct sunlight provides more heat than angled (indirect) sunlight.

  1. Give small groups two pieces of graph paper and a flashlight. Ask them to lay one piece of paper on a surface horizontally to represent the Earth, shine the flashlight directly on it from about two feet away, and trace the outline of the light.
  2. Ask students to change the angle of the second piece graph paper (for instance, by lifting it up a bit) to simulate the Earth’s tilt in relation to the sun. They should place a notebook or other hard surface behind it, again shine the light on it from the same location, and trace the outline of the light.

Making Connections Journaling and Discussion Questions

  • What do you notice about the amount of sunlight hitting each piece of paper?
  • Which season do you suppose each piece represents and why?
  • How do these findings, along with your investigations in part one, help you better understand the seasons?
    (When our hemisphere is tipped away from the sun during the winter, the angled sunlight is spread over a greater area, so it not very intense and doesn’t provide as much heat as when it hits us more directly during the summer.)

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