Angle of Sunlight

Earth Systems Standard 6, Objective 2

Title: What’s the Angle?

Brief Description: Students record shadow length, once a week, over a period of one to two months, and note changes in the sun’s angle according to season.

Objective: Students will determine the relationship between the angle of the sun and the length of shadow it projects. Students will understand how the tilt of Earth causes this angle change, and affects temperatures in certain regions and thus causes seasons. This is a key factor in climate.

Materials needed: rulers

Background Knowledge: Students should understand the angle of isolation and solar radiation. It would be helpful to complete the “Angle of Insolation” lab before you begin this lab.

Time needed: Lab Introduction 30 minutes Data recordings 10 minutes each time (4X) Lab Analysis Questions 25 minutes Time extends over a 4-8 week period

Safety/Security Concerns: None

Notes to Teacher: Each data collection should be recorded at the same time of day. The longer you collect data, the clearer the pattern will be to your students. Plan to avoid a daylight savings change but if you can chart the sun over a solstice (Dec. 22 most likely) this would be very instructive.

Teacher procedures: 1. Assemble needed supplies. 2. Run off enough copies of the student sheets for all participating students. 3. Hook: When students arrive in class have them all follow you outside. Have students stand in a single file line so each person can see his or her shadow. (Do this without telling them why they are facing the direction they are.) Direct students attention to their shadows. Ask for several volunteers to explain what they think will happen to their shadow as the day progresses. Take as many responses as you get. Come to a class consensus. Hopefully students should realize that their shadow will get shorter as noon approaches and longer past noon. Bring students back to the classroom. 4. Ask if anyone knows how your shadow might change throughout the year. Take any responses. Tell the students they will be collecting data on shadow length for the next few weeks to answer this question. 5. Pass out the student sheets. Allow students to read through the background information in their labs. 6. Review with students what the angle of insolation means. 7. Have students read through the lab procedures and make their predictions. 8. Allow students to 10 minutes once a week to collect data. 9. Provide time for students to answer questions when data collection is complete. 10. Discuss questions.

Answers to Analysis Questions: 1. The angle of sunlight gets larger as summer approaches. 2. Higher 3. Warmer because the solar radiation is more direct, it is not scattered as it would be at a smaller angle. 4. This marks a turning of the seasons, the days become shorter because the sun is not as high in the sky. The smaller the angle the cooler the temperatures will become as the radiation begins to scatter more and more as the winter solstice approaches. 5. The suns angle changes because the earth is tilted on its axis. As it rotates around the sun sometimes the northern hemisphere is tilted towards the sun and at other times the southern hemisphere is tilted towards the sun. 6. When a hemisphere is tilted towards the sun the angle of insolation is greater because the sun is higher in the sky. The will cause a warm season. When the hemisphere is tilted away the opposite occurs. This is the cause of the seasons, seasons are a part of the climate of an area because they affect long term weather patterns. 7. The earths distance from the sun at various points in its rotation is irrelevant. The seasons are caused by the tilt of the earth affecting the angle of insolation. The earth is actually closer to the sun in the winter. 8. Not significantly. This means there are no significant seasonal changes. The climate remains the same throughout the year. 9.

Summer

Winter 10. Rate of change should be consistent between all students (within reason). The rate of change would be greater the further you are from the equator, with the greatest change at the poles.

Conclusions: Answers will vary but should be detailed and relevant. Students should also use complete sentences.

Sample Grading Rubric: Points Requirement Possible Prediction 1 Data Table Complete 6 Analysis Questions answered correctly 20 Conclusions valid and complete 4 Graph, labeled, colored, accurate, clear 4 Total 35 Student Sheet Name______Date______

Title: What’s the Angle?

Background Information: Solar radiation from the sun strikes Earth at different angles depending on latitude, time of day, and the time of year. The angle at which the suns rays hit Earth is called the angle of insolation. The angle of insolation changes, depending on latitude, because of the spherical shape of Earth. At the equator the suns rays are most direct, striking at a 90 angle. This provides the most concentrated solar radiation, correlating to warm temperatures. At the poles, Earths surface is curved, causing the solar radiation to hit at a much smaller angle. This spreads the radiation out over a greater distance, providing the least concentrated radiation. Scattered radiation correlates to colder temperatures. The angle of insolation changes depending on the time of day because of the rotation of Earth on its axis. This causes the sun to appear to rise and set. At sunrise and sunset the sun is low on the horizon striking Earth at a smaller angle. This scatters the radiation and correlates to cooler temperatures in the morning and evenings. At midday the sun is at its highest point in the sky giving the most direct radiation. As Earth orbits around the sun, throughout the calendar year, the angle of insolation changes. This is because Earth is tilted slightly on its axis. In this lab you will be investigating how that tilt affects the angle of insolation and in turn causes the seasons experienced in latitudes away from the equator.

Objective: To see how the angle of the suns rays changes over time and to relate this to seasonal climate changes.

Materials: 2 rulers

Procedures: 1. Stand one ruler up straight, touching the ground. 2. Measure the length of the shadow. 3. Record in data table. 4. Repeat once weekly, at the same time of day. 5. Answer analysis questions, make graph, and draw conclusions.

Prediction: What will happen to the length of the shadow as time progresses? Quantitative Data: Date and Time Length of Shadow (centimeters)

Graphs:

Make a line graph showing how the length of shadow changed over time. Be sure to label your axis.

Analysis Questions: 1. What happens to the angle of sunlight as summer approaches?

2. Is the sun higher or lower in the sky?

3. Are the suns' rays warmer or colder at these angles? Why?

4. The summer solstice is June 22. This is when the angle of the rays starts to get smaller again. Why is this an important day?

5. Why is does the suns angle change as the year progresses?

6. How does this relate to seasons and climate?

7. Many people think is colder in the winter because Earth is farther from the sun. Is Earth farther from the sun in winter in our hemisphere?

8. Does the angle of insolation change at the equator throughout the year? What does this mean about the climate at the equator?

9. Draw a diagram representing the position of Earth on its axis during each of the seasons. Draw the angle of insolation as well.

10. What was the rate of change for the shadow? How would this rate of change vary depending on your latitude?

Conclusions: Please explain two things you learned from completing this lab. Be sure to use complete sentences.