1. Watch the NASA video “What are sunspots?”
Show students the NASA video “What are sunspots?” Provide support for vocabulary terms sunspots, magnetic field, photosphere, convection, and atmosphere, as needed. Then check students’ understanding. Ask students to restate the comparison of sunspots to light bulbs in their own words.

2. Introduce the activity and safety concerns.
Explain to students that looking directly at the sun is very dangerous and can cause permanent damage to human eyes. Make sure that students understand that no one—not even scientists—ever look directly at the sun. Instead, scientists use methods that allow them to observe the sun indirectly. In this activity, students will build a pinhole viewer that will allow them to observe the sun indirectly and safely.

3. Have students build a pinhole viewer to view sunspots.
Divide students into small groups of 3 or 4. Before students begin, project the step-by-step illustration for them to refer to as they build their viewers.

• Take the cardboard box and cut a 2 centimeter x 2 centimeter hole at one end.
• Tape a piece of aluminum foil over the hole, making sure it is taut.
• Carefully use the pushpin or sewing needle to poke a hole into the foil.
• At the opposite side of the box, cut a small window about 1 centimeter from the end. The window should be no larger than 10 centimeters x 3 centimeters. Make sure that the window is no wider than the side of the box.
• Tape a piece of white paper to the inside of the box. This will be your viewing screen.
• Aim the pinhole side of the projector at the sun. Keep positioning the projector until you have the image of the sun on your screen. It will appear to be a white disk.

4. Have students make a math connection.
Tell students that they can gather data from their sunspot viewer activity to calculate, or figure out, the diameter of the sun. First model, and then have them do the following steps in order:

• Draw a circle around the image of the projected sun on the paper. Find the center of the circle by folding the circle twice making sure the outer edges of the circle line up. For a more precise method, students can use the chord bisector method, described below. Place a dot in the exact center of the circle.
• Draw any two chords, or line segments that cross in two places on the circumference of the circle.
• Draw a line segment perpendicular (at a 90° angle) to the chord toward the center of the circle.
• Repeat with the second chord.
• Find the center of the circle at the point where the two perpendicular lines drawn intersect or cross.
• Then, use a ruler to measure the distance from the center of the circle to one side of the circle in centimeters. This is the radius of the circle. Multiply the radius by 2 to calculate the diameter.
• Use a ruler to measure the distance from the pinhole to the paper. The pinhole is on the opposite side of the box from the paper. Calculate the distance by measuring the length of the box. Measure using centimeters.
• Finally, use this formula: Diameter of the image of the sun ÷ distance from the pinhole to the paper × distance from Earth to sun, approximately 149,600,000 kilometers (92,957,130 miles) = diameter of the sun

Note that students should arrive at a result for the diameter of the sun that is approximately 1.4 million kilometers (870,000 miles). Explain the relative size of the Earth and the sun. Tell students that the sun’s diameter is about 100 times that of the Earth.

5. Have students use their pinhole camera to track sunspots over a period of time.
Explain to students that sunspots can serve as markers to help us see the sun’s rotation. Distribute one copy of the worksheet Sunspot Mapping Grid to each group. Ask groups to sketch and label each sunspot for 10 days.

6. Have a whole-class discussion about what students observed over time.
After students have tracked sunspots for ten days, have a whole-class discussion about what they observed. Ask:

• Have the sunspots moved? Describe their movement.
• Have the shapes and sizes of the sunspots changed? How?
• Are there fewer sunspots or more sunspots? Why do you think that is?
• What did you learn about the sun’s rotation by tracking sunspots over time?

Students should understand that the sun rotates, which causes sunspots to vary over time in a regular and somewhat predictable way.