How does the angle and area of incident sunlight change as you move away from the Equator towards the poles?

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1 Environmental Literacy Framework Flashlights on Earth Focus Questions: How does the angle and area of incident sunlight change as you move away from the Equator towards the poles? Have you ever wondered why it was so much less bright in the morning and evening than at noon on any given day? Or, if you live in higher latitude regions, such as the northern United States, have you noticed how the sunlight angles change from month to month causing a cooling in the fall? Time 1 class period for set up 1 class period to explore. Materials Preview The Sun s energy travels to Earth in the form of electromagnetic radiation. This solar energy travels 93 million miles (150 million km) through space from the Sun to Earth. We sense solar radiation in the form of heat and light. Solar radiation is the energy that drives many of the processes acting on the surface of Earth as well as life itself. Solar radiation that makes it through the atmosphere to Earth s surface is called insolation. On average, 342 watts/meter squared (W/m2) of solar energy reaches the Earth's outer atmosphere. More energy is received at the equatorial regions than at the poles. The change in the insolation angle is due to the fact that Earth s axis is tilted and Earth is round, not flat. Therefore the equatorial regions of Earth receive light that is nearly perpendicular (90 ) to the surface. As you move toward the polar regions, the angle of light decreases, and the area over which radiation is spread increases. This reduces the intensity of light and therefore the amount of incoming solar radiation per square meter.think for a moment of spreading jam on a bagel the larger the area of the bagel that you cover with jam, the less intense the flavor! Because the angle of incidence is lower at the polar regions, less solar radiation is available to be absorbed by the land and ocean, making them colder. However, thanks to the air and ocean currents, heat energy is transported from one area of Earth to another. This transfer of energy from warmer to cooler regions of the Earth helps to stabilize the climate of the planet. Inflatable globe with continents, 1 large, strong, focusable flashlight, such as a Maglite brand flashlight 3 smaller Maglite type flashlights Several cups or plastic bowls to act as a base for the flashlight and globe Shoebox to hold small flashlights Books, bowls and other objects to help prop up the shoebox and globe Clipboard to hold graph paper Graph paper Ruler and protractor Sharp knife for cutting hole in shoebox (adult supervision needed for this step) Hot glue gun (optional) Masking tape Pen for marking on shoebox Vocabulary (Terms) Angle of incidence Electromagnetic spectrum Insolation Solar radiation 3

2 Environmental Literacy Framework Activity 1A-Flashlights on Earth Prepare: This activity is presented in three parts. Part 1: Spreading the Light Around 1. Place a sheet of graph paper in the clipboard. Set a protractor on the table. Hold the clipboard and paper at a 90-degree angle to the beam of light (and to the table). This angle is perpendicular to the light beam. 2. In a darkened room, hold the flashlight approximately 50 cm (20 in) away from the paper and measure the distance. It will be important to have the same distance between the light and the clipboard each time. 3. Turn on the flashlight so that it is shining on the paper. Use a pencil to trace around the area on the graph paper that is lit by the light. (This is the 0-degree angle shown in the picture below.) Count the squares that are included in the circle. Partial squares may be included in the count. Record the number of squares on a separate piece of paper. 4. Tip the clipboard away from the flashlight, 45 degrees away from the initial 90- degree (perpendicular) position, or to an angle of 45 degrees on your protractor. Repeat the tracing, measurement and recording of number of squares, or simply observe the change. 5. Repeat the process again at a 30- degree angle from the perpendicular, or to 60- degrees on your protractor. 6. What changes in the circles do you observe? The flashlight remains stationary; all that changes is the angle of the clipboard. 4

3 Activity 1A-Flashlights on Earth Part 2 A: 1. Set your inflatable globe in a bowl on the tabletop. 2. Set the large flashlight on a bowl and tape it in place. Adjust the height of your flashlight to center on the Equator. Adjust the focus of the light to a tight circle by moving the flashlight and bowl closer to or farther away from the globe. 3. Darken the room so that you can see the light on the globe. 4. Explore tilting the axis of the globe towards and away from the light source. How does the circle of light change as you tilt the globe? Globe and flashlight on workbench after the clipboard activity, 5

4 Activity 1A-Flashlights on Earth Part 2 B: After you have explored one light source, use a shoebox to build a simple support mechanism to hold three small flashlights. 1. Measure the length of the shoebox. Locate the center and mark an x with a pen. Measure two inches away on each side of the center mark, and make two more marks. You should now have three equally spaced x marks on your shoebox. 2. Use a sharp knife to cut two perpendicular slices at each mark. Safety Note: Ask an adult for help with the knife. Make the cuts small at first, just large enough for the base of the flashlight to fit through the hole. You can enlarge them as needed. 3. One at a time, insert each of the three flashlights into the holes. Adjust them so that they are level, and make sure that you can turn them on. Once you have them in place, use masking tape to secure them. Optional: Hot glue the lights to the box after you have adjusted them. 4. Set your globe in front of the flashlights, and adjust the height so that the center flashlight is aimed at the Equator. Turn on the flashlights and adjust the focal length, by sliding the globe closer to or farther from the shoebox, so that all three flashlights are creating tight areas of light on the globe. You should see three distinct circular areas on the globe. Look carefully at the globe; are the light areas all the same shape and area? 5. Observe and measure the length and width (area) of each of the light circles. Note how they change from the center of the globe (Equator) to the poles. Record this information in your science journal. Sketch the shape of the circles of light at each location. Compare the shapes of the circles to the circles on the graph paper in Part 1. Photos: Betsy Youngman 6

5 Activity 1A-Flashlights on Earth Practice Got the Big Idea? Solar insolation varies from the Equator to the poles. Due to this variation, the polar regions are colder and the equatorial regions are warmer. Incoming solar radiation measured at Earth's surface averaged over a 10-year period. Colors are values in kilowatt hours per square meter per day. Because the measurements are taken at Earth's surface, clouds (particularly in the tropical regions) have reduced the amount of solar energy. Image source: (Hint: may need to copy link into your browser.) 7

6 Activity 1A-Flashlights on Earth Ponder How are the light circles changing as you move north and south away from the Equator? How about from west to east across the Equator around the globe? Graphic: Rita Thomas, ANDRILL Science Management Office, University of Nebraska-Lincoln Axis Earth is tilted 23.5 degrees from perpendicular North Pole Sun s rays Equator South Pole Sun s rays Direction of Earth s Spin Present Special preparations for this station Make sure that you have plenty of fresh batteries for your flashlight. Place this station in a dark corner of the room or in a separate location for maximum effect. Repeat the previous activity steps to guide your audience's investigation. 8

7 Activity 1A-Flashlights on Earth Background Information for the Teacher 9 Activity In this hands-on activity, learners create a model to show how the angle of the Sun s incoming rays, due to the shape and tilt of the Earth, affect the amount of energy reaching the Earth s surface. Students explore the relationship between solar intensity and the incoming angle of the sunlight, also known as the angle of incidence. NSES 5-8 CLEP ELF Science as Inquiry Std A: Mathematics is important in all aspects of scientific inquiry. Physical Science Std B: Energy is transferred in many ways. Heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature. Light interacts with matter by transmission (including refraction), absorption, or scattering (including reflection). The sun is a major source of energy for changes on the earth's surface. The sun loses energy by emitting light. A tiny fraction of that light reaches the earth, transferring energy from the sun to the earth. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation. Earth Science Std D: The sun is the major source of energy for phenomena on the earth's surface, such as growth of plants, winds, ocean currents, and the water cycle. Seasons result from variations in the amount of the sun's energy hitting the surface, due to the tilt of the earth's rotation on its axis and the length of the day. Principle 1: The sun is the primary source of energy for Earth's climate system. 1C: The tilt of Earth s axis relative to its orbit around the Sun results in predictable changes in the duration of daylight and the amount of sunlight received at any latitude throughout a year. These changes cause the annual cycle of seasons and associated temperature changes. Energy 1: Solar energy is the driving force for Earth s climate system. Energy 1a: Solar energy measured at the Earth s surface (insolation) varies due to Earth s shape, its orientation with respect to the Sun, and the characteristics of its orbit around the Sun. Earth s tilt and orbit cause the annual cycle of seasons and associated temperature changes. Cyclical, long-term changes in Earth s orbit and tilt, called Milankovitch Cycles, have profound effects on insolation and therefore global climate.

8 Activity 1A-Flashlights on Earth NSES: National Science Education Standards ( CLEP: Climate Literacy Essential Principles ( ELF: Environmental Literacy Framework ( Additional Information: Climate and Earth s Energy Budget Background Information One could say that we live on a solar-powered planet. The solar radiation that reaches Earth s surface is the energy that drives many of the processes acting on the surface of the Earth, including our weather and climate, wind and ocean currents, and life-giving photosynthesis. The Sun s energy travels to Earth in the form of electromagnetic radiation. Solar energy travels 93 million miles (150 million kilometers) through space, from the Sun to Earth. Because of the distance that it travels, solar radiation contacts the Earth's surface in essentially parallel lines. Solar radiation that makes it to Earth s atmosphere and surface is called solar insolation (this is short for incoming solar radiation). Satellite measurements have shown that on average, 342 watts per square meter of solar radiation reaches the top of Earth s atmosphere. About 70% of that energy (in the form of visible and infrared light) makes it through the atmosphere and enters the Earth s climate system. We sense this incoming solar radiation in the form of heat and light. Because the angle of incoming sunlight is lower at higher latitudes, and it must travel through a greater amount of atmosphere, more energy is absorbed by the atmosphere. For these two reasons, less solar radiation is available to be absorbed by any given area in the Polar Regions, making them colder. However, thanks to the air and ocean currents, absorbed heat energy near the Equator is transported (via convection, conduction, and evaporation) to the Polar Regions. This transfer of energy from warmer to cooler regions of the Earth is important because it helps to stabilize and equalize the climate of the planet. Presently, the Earth s axis is tilted at an angle of 23.5 to the plane of its revolution around the Sun. Therefore, over the course of a year, as Earth revolves around the Sun, its inclination angle towards the Sun also changes. This change causes a variation in the light (and heat) intensity that occurs on Earth s surface. 10

9 Activity 1A-Flashlights on Earth Additional Resources: Image source: Image source: 11

10 Activity 1A-Flashlights on Earth Glossary Unit Activity Vocabulary Word Definition Energy Energy Flashlights on Earth Flashlights on Earth Energy Flashlights on Earth Energy Flashlights on Earth Angle of Incidence Electromagnetic Spectrum Insolation Solar Radiation An angular measurement of an object away from 'straight up' (E.g., if a flagpole is perpendicular to the ground, it has an angle of incidence of 0 o. If it is tilted to one side, its angle of incidence is the degrees from perpendicular.) The range of all possible frequencies of electromagnetic radiation (Short frequency waves, such as x-rays, are high energy; longer waves with lower frequencies, such as radio waves, have lower energy.) The amount of solar radiation received by the Earth in a given area in a given time, usually expressed as watts per square meter, W/m 2 We experience solar radiation as visible light, heat (thermal energy), and ultraviolet light. Its source is the Sun. 12