GO IN DEPTH

# Star Power! Discovering the Power of Sunlight

Photo Credit: Clipart.com.

### Purpose

To estimate the energy output of the sun and how much power sunlight provides to the earth.

### Context

This lesson was developed by the Challenger Center as part of NASA's MESSENGER Mission, of which Science NetLinks is a partner.

In this lesson, students will discover that sunlight and the electromagnetic spectrum are the main tools with which we study objects in the solar system. They will also learn that the sun is the main source of energy on earth. As part of an experiment, they will build a simple device to measure the amount of solar radiation the earth receives from the sun. They will be able to do this by measuring the temperature change in a bottle of water as it is exposed to sunlight. Then, using this data and other parameters of the experiment, they will calculate the solar constant, which is the amount of energy the earth receives from the sun per square meter per second. They will also be able to describe the difference in the amount of solar radiation emitted at Mercury as compared with the Earth.

Refer to the Science Overview section of the lesson for a summary of the science content relevant to the activities in the lesson. In order to successfully complete this activity, students should already have had some instruction in heat and energy transformations. Refer to the Lesson Overview for a more detailed explanation of what students will learn from the lesson.

While teaching, keep in mind that heat energy is a surprisingly difficult idea for students, who thoroughly confound it with the idea of temperature. A great deal of work is required for students to make the distinction successfully, and the heat/temperature distinction may join mass/weight, speed/acceleration, and power/energy distinctions as topics that, for purposes of literacy, are not worth the extraordinary time required to learn them. (Benchmarks for Science Literacy, p. 81.)

In addition, it is worth noting that research shows that high-school students do not always explain heat-exchange phenomena as interactions. For example, students often think objects cool down or release heat spontaneously—that is, without being in contact with a cooler object. Even after instruction, students don't always give up their naive notion that some substances (for example, flour, sugar, or air) cannot heat up or that metals get hot quickly because "they attract heat," "suck heat in," or "hold heat well." Also, few high-school students understand the molecular basis of heat transfer even after instruction. Although specially designed instruction appears to give students a better understanding about heat transfer than traditional instruction, some difficulties often remain. (Benchmarks for Science Literacy, pp. 337-338.)

Studies also show that students' meanings for "energy" both before and after traditional instruction are considerably different from its scientific meaning. In particular, students believe energy is associated only with humans or movement, is a fuel-like quantity which is used up, or is something that makes things happen and is expended in the process. Students rarely think energy is measurable and quantifiable. (Benchmarks for Science Literacy, p. 338.)

Note: Parts of this lesson were extracted from the unit, Staying Cool, developed by the Challenger Center as part of NASA's MESSENGER Mission.

### Motivation

Have students do the activities in the Warm-Up and Pre-Assessment section of the Lesson Plan. These activities are meant to help you find out what students already know about heat, temperature, and how earth and other planets in the solar system are affected by the power of the sun. They will be prompted to think about how the amount of sunlight falling on earth can be measured and or calculated. The concept of the solar constant will also be discussed to orient them on the main thrust of this lesson—to build a device that measures the solar constant, or the amount of solar radiation emitted on earth.

### Development

As noted in the Procedures section of the Lesson Plan, you should divide the class into groups of three, with each group building and testing the measuring device by carefully following the instructions on the Measuring the Solar Constant student sheet. When all of the data has been collected and recorded, students will need to calculate class averages, which should be noted on a chart like the one in the Procedures section. (This information will be necessary for them to complete their calculations on their worksheets.)

As part of the Discussion and Reflection phase of the Lesson Plan, students will have to come up with reasons why there are deviations in the values of the solar constant between groups, which is a very likely outcome. Have students discuss what it is they measured and how it relates to the power of the solar system. Also have them consider the role of the sun on Earth and how it will impact the MESSENGER mission to Mercury. Students will learn about these ideas from their MESSENGER Information Sheet.

Finally, students may further apply what they have learned by calculating planetary temperatures using the Sun's Effect on Planetary Temperatures student sheet as well as the potential of solar power using the Potential for Solar Energy Use student challenge sheet. Time permitting, these additional student sheets may be filled out in class or given as homework.

The Answer Key provides answers for all three student sheets in this lesson.

### Assessment

Remind and summarize what students have learned in the Closing Discussion section of the Lesson Plan, particularly how they discovered the central role sunlight plays in our lives by calculating the amount of energy it provides to earth. The importance of sunlight for planetary exploration, including the MESSENGER mission, should also be discussed.

Further assessment can be made by using pages 3-5 of the Measuring the Solar Constant student sheet, as well as pages 2-3 of the Sun's Effect on Planetary Temperatures student sheet and the Potential for Solar Energy Use student sheet.

Note: The Assessment section features a number of ideas for additional class assignments.

### Extensions

For related Science NetLinks lessons, see:

The device used in the experiment of this lesson can be modified to make it a more accurate, sophisticated measuring tool. A number of adaptations are noted in the Extensions section of the Lesson Plan.

Have students examine the history of the study of the sun. Have them write a timeline or essay about which scientists made important discoveries about the sun and when.

Have students research ways that solar radiation can be captured and applied to advance technology and cut back on the use of fossil fuels. Discuss the practicality, as well as the advantages and disadvantages, of this technology.

Solar energy is a growing alternative to other natural resources. Discuss the advantages solar power has with regards to the environment, as well as any disadvantages.