Reasons for Seasons
Following the Sun Through the Year
Creating an Earth/Sun Model

1-2 periods and then a few minutes each month

clear 2-quart bowl, large sheet of white paper taped to a piece of cardboard or other rigid item, sharp pencil, erasable marker, compass, crayons or colored pencils

Teacher Background

Overview: Students create a simple model of the Earth and sun as seen from space. They use it to explore the sun's apparent movement across the sky over the course of a year. They note the changes in the sun's angle. The begin to understand that it appears lowest in the sky on the winter solstice and highest on the summer solstice. This lays the groundwork for understanding the reasons for seasons and for making sense of Mystery Class photoperiod clues.

Preparation: Plan to conduct this on a sunny dry day around the 20th of September (close to the Fall Equinox).

Laying the Groundwork
Invite students to imagine they are far out in space and can see the Earth and our sun. Ask, What would you expect to see happening and why? Make four different drawings to show what you'd see during each season. Once students have completed this, ask, What questions do you have? Save these for students to revisit later in the activity.

Click for larger image.
  1. Make an X in the center of the paper to represent our Earth.

  2. Take the materials outside. Find a level surface for the paper. Make sure the location receives sunlight all day.

  3. Place the bowl upside down on the paper. Ask students to imagine it's our atmosphere. Mark an x on the center of the bottom of the bowl with the overhead marker. Make sure the x on the paper is lined up under the x on the bowl. Trace the edge of the bowl onto the paper to make it easier to line up.

  4. Have students use a compass to determine North for your location. Once they've reached consensus, they should mark North on the paper and the bowl.

  5. Have a student touch the side of the clear bowl with the tip of the pencil so the shadow of the pencil's tip falls on the X on the paper. Have a partner make a dot on that spot with the marker. (They can put a number or date beside each dot to recall the order in which they made observations.) After each dot goes on, ask students, Where do you predict the dot will be next month? Explain your thinking. Which direction does the sun appear to be moving?

    Note: To get accurate results, the bowl must sit in the same location and be lined up in the same way for each monthly reading.

  6. Repeat this activity each month. Use one color overhead marker from September through December and another color from January through June. If this is done on or about the 20th of each month students will see what happens on the fall and spring equinox and the winter solstice. Their marks will indicate the changes in the angle of the sun throughout the year.

Making Connections — Discussion and Journaling Questions

  • What patterns did you notice over the course of the year?
  • How would you explain them?
  • What general statement(s) could you make about the yearly movements of the sun and earth?
  • What questions do you still have?
  • What does this "tell you" about the seasons?
  • If you noticed that the sun appeared higher in the sky than it was a month ago, which seasons could it not be? Explain your thinking. (It couldn't be fall, because the sun appears lower in the sky from month to month in the fall.)

    What to Expect
    As students mark the sun's apparent movement throughout the year, they'll find that it appears lower and lower from the fall equinox through the winter solstice. It appears lowest in the sky (the greatest angle) on the winter solstice and then begins to appear higher and higher until the summer solstice, when it's at its highest point. It is somewhere between the two on the equinoxes. (See the glossary definitions and images of the sun's location on the solstices and equinoxes.)

Once students have completed the exploration, ask them to revise the drawings they made during Laying the Groundwork. They can either create new ones or use another color to make changes. Their responses to the discussion and journaling questions along with the changes in their drawings should reveal an enhanced understanding of the seasonal Sun-Earth relationship. Also see these assessment tasks.

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