Part2: Build Your Own Planet

Part2: Build Your Own Planet

Lesson 3: Albedo

Time: approximately 40-50 minutes, plus 30 minutes for students to paint pop bottles

Materials: Text: Albedo (from web site – 1 per group)

Small thermometers, at least 0ºC to 100ºC range (2 per group)

If performed outdoors:

Plastic 2-liter soda pop bottles (2 per group)

1 can of flat white spray paint

1 can of flat black spray paint

If performed indoors:

Ring stand (1 per group)

Small lamp with outdoor floodlight or 100W light bulb (1 per group)

Black construction paper (2 sheets per group)

White construction paper (2 sheets per group)

Overview

Students explore the effect of bond albedo on a planet’s surface temperature. They will measure the temperature of the air under black and white bottles and use this information to draw conclusions about how the amount of energy reflected away from a planet affects its average surface temperature.

Purpose

Students will learn that light colors reflect more energy than dark colors. As a planet’s albedo increases, its average surface temperature will decrease. Students should learn that they can influence the average surface temperature of their planets by manipulating their planet’s bond albedo.

Standards

A complete list of the standards covered by this lesson is included in the Appendix at the end of the lesson.

Procedure

Have the groups read the introduction to the lesson and make a prediction.

Does the surface of a planet affect how warm or cold it is? If so, how? This lesson will explore these questions.

Not all the energy that arrives at a planet actually warms the planet. Some of it is reflected back into space. The measure of the amount of energy reflected back into space is called the “ALBEDO” of the planet. (Albedo can be measured different ways. For this unit we will be using a particular type of measurement called “BOND ALBEDO.”)

Rocky surfaces can vary in color, but are usually dark. Icy surfaces can be very light or very dark depending on how much dust is mixed in with the ice—the more dust mixed in, the darker the ice. Liquid surfaces tend to be less dark than rocky surfaces.

Before we do the experiment, discuss the following question with your group and make a prediction: Will a dark-colored surface reflect more or less heat away from a planet than a light-colored surface?

Prediction: A dark colored surface will reflect ______heat.

(more or less)

Instructors should decide whether to prepare the painted 2-liter pop bottles themselves or to let the students prepare them. It is important that flat paint is used. Gloss or semi-gloss paint may give ambiguous results.

One can of spray paint is usually enough to paint 8 to 10 bottles, both inside and out. Painting both inside and outside will give the best results. Set the bottles on the ground to paint the inside and then wait at least 15 minutes for them to dry to the touch. While drying, hammer a 3’ to 4’ long stake or stick into the ground. After 15 minutes, place the bottle upside down over the stick and spray paint the outside. Wait 5 minutes and then check that bottles are evenly covered. It is probably a good idea to prepare the bottles a day in advance, although the bottles should be useable within 1 hour after painting with most types of flat spray paint.

Experiment: Testing the Effect of Albedo on Temperature

You will need:

This worksheet

2 plastic two liter pop bottles

2 small thermometers

Flat black paint

Flat white paint

Step 1: Cut off the top of the two plastic pop bottles at the top of the label. Remove the labels.

Step 2: Paint the outside of one of the bottles black and the other bottle white. You should also paint the inside of the bottles if you have enough paint.

This lesson can be done in lightly overcast weather, but the results will be more noticeable in full sunlight.

On a sunny day:

Step 3: Place both thermometers in a refrigerator for at least 5 minutes (longer is fine).

Step 4: Remove the thermometers from the refrigerators. Bring this worksheet, both thermometers and the two painted bottles outside into the Sun.

The thermometers do not have to be expensive. They must be short enough to fit under the bottles. If they are short enough to lie flat under the bottles then care must be taken to ensure that the thermometers record the temperature of the air under the bottles and not the temperature of the surface that they are lying on. On very warm or very cold days the temperature of the ground may be very different from the air temperature. This can create inaccurate measurements. The problem can be remedied by having groups bring out a book large enough to place both bottles on. The groups can place both thermometers on the book and then cover the thermometers with the bottles.

Teachers should caution students to be careful where they stand during the test so that their shadows are not falling on either of the bottles.

Step 5: Place the thermometers on the ground. Cover one with the white bottle and the other with the black bottle. (If the thermometer is longer than the diameter of the bottle you will need to stand the thermometer up inside the bottle.) Wait at least three minutes.

Step 6: Lift up the white bottle and check the temperature on the thermometer. Record the temperature here: ______º F / C (circle).

Note: Circle “F” if you recorded the temperature in degrees Fahrenheit. Circle “C” if you recorded it in degrees Celsius. Make sure to use the same temperature scale throughout this experiment.

Step 7: Lift up the black bottle and check the temperature on the thermometer. Record the temperature here: ______º F / C (circle).

Inexpensive classroom thermometers can be inaccurate. By switching the thermometers and repeating the test any inaccuracies will be canceled out. Teachers may consider eliminating the explanation below from the student copies of the assignment and asking students how they might compensate for any potential inaccuracies.

Because there might be small differences in the thermometers, we need to swap the thermometers between the two bottles and repeat the experiment, so continue on to Steps 8 - 10.

Step 8: Take the thermometer that was under the white bottle and place it under the black bottle. Put the thermometer that was under black bottle under the white bottle. Wait at least three minutes.

Step 9: Lift up the white bottle and check the temperature on the thermometer. Record the temperature here: ______º F / C (circle).

Step 10: Lift up the black bottle and check the temperature on the thermometer. Record the temperature here: ______º F / C (circle).

Step 11: Add together the two temperature readings under the white bottle recorded in Steps 6 & 9.

Total temperature under the white bottle: ______º F / C (circle).

Add together the two temperature readings under the black bottle recorded in Steps 7 & 10.

Total temperature under the black bottle: ______º F / C (circle).

Questions:(Answers included)

1) Which color bottle had the higher total temperature?

______.(Black)

2) Which color bottle had the lower total temperature?

______.(White)

3) Which color bottle reflected away more heat?

______.(White)

4) Since albedo is the measure of how much energy is reflected away, which color bottle had the higher albedo?

______.(White)

5) Was the difference in total temperature between the two bottles great or small?

______. (Either answer is permissible depending on the group’s perspective, but albedo has a smaller impact on a planet’s average surface temperature than the mass of the star it is orbiting or its distance from that star.)

6) Do you think albedo has a great effect or a small effect on a planet’s surface temperature?

______.(Either answer is permissible as long as it is consistent with the group’s answer to question 5.)

Based on what you just discovered about the black and white bottles, circle the correct answers to the next three questions.

Answers are given in bold.

7) If all other conditions were the same, you would expect a planet with a high albedo to have a (higher / lower) average surface temperature than a planet with a low albedo.

8) If all other conditions were the same, a planet with a dark-colored surface would have a (higher / lower) average surface temperature than a planet with a light-colored surface.

9) Much of the Earth’s north and south Polar Regions are covered by ice caps. This ice is very light-colored, almost white. This means that the ice caps have a (higher / lower) albedo than the rest of Earth’s surface. As the ice caps melt and become smaller the Earth’s albedo (increases / decreases) and the Earth becomes (cooler / warmer). If the ice caps start increasing the Earth’s albedo would (increase / decrease) and the Earth would become (cooler / warmer).

Slide #1 can be used when discussing the above question.

10) In your own words, explain how the average surface temperature of a planet changes as its BOND ALBEDO changes. ______

______

11) Now think about the average surface temperature of the planet you are exploring. Based on what you have discovered with the Planet Temperature Calculator, is the average surface temperature of your planet too hot, too cold or about right? ______. Do you want your planet to have a high or a low albedo? ______

Slides #2-3 can be used when discussing the following question.

Look at question 5 of the Planet Preference Survey to find the type of surface you selected for your planet. The surface you chose will restrict the range of numbers that you may enter for BOND ALBEDO in the planet temperature program.

If you chose “Liquid” choose a number between 15 and 25.

If you chose “Solid” choose a number between 1 and 15 for a rocky surface, 50 and 80 for a fresh ice covered surface, or 10 and 50 for an old, dirty ice covered surface.

If you chose “Mixture” decide whether your planet is mostly rock, mostly liquid or mostly ice. You should choose a number close to the allowable range for that surface (check the ranges listed above) but it can be a little higher or lower, depending on what else is on your planet’s surface.

Our planet has a BOND ALBEDO of ______.

The groups should use this value for BOND ALBEDO for the remaining lessons of this unit.

While it is recommended that this activity be performed outdoors, it is possible to modify it so that it can be done indoors if the weather does not cooperate. The following is the procedure for a similar indoor activity:

1)Suspend the lamp upside down in the ring stand so that the floodlight or 100W light bulb is pointing downward.

2)Adjust the ring stand so that the floodlight bulb is approximately 6” (15 cm) above the table top, or 4” (10 cm) if using a 100W bulb.

3)Place one sheet of white paper and one sheet of black paper side-by-side under the light bulb. Adjust the ring stand so that the center of the bulb is directly over the line where the two sheets of paper meet.

4)Place one thermometer on the white paper approximately 3” (8 cm) from the line where the 2 sheets of paper meet and the other thermometer in the same relative position on the black paper. If desired, teachers can have students measure and mark the positions on the papers where the thermometers will be placed beforehand, although this is not critical. It is important, however, that both thermometers are about the same distance from the bulb.

5)Cover the thermometer on the white paper with the 2nd sheet of white paper and the thermometer on the black paper with the 2nd black paper. The top and bottom papers should all meet at the same line.

6)Turn on the light bulb and wait approximately 3 minutes if using the floodlight or 5 minutes if using the 100W bulb.

7)Uncover the thermometer on the white paper and record the temperature.

8)Uncover the thermometer on the black paper and record the temperature.

9)Switch the thermometers and repeat.

Students will need a different worksheet if performing this activity indoors. A modified worksheet is available in Appendix B

Appendix A

Standards Addressed

Benchmarks (Grades 3 through 5)

1B – Scientific Inquiry

Scientific investigations may take many different forms, including observing what things are like or what is happening somewhere, collecting specimens for analysis, and doing experiments. Investigations can focus on physical, biological, and social questions.

Results of scientific investigations are seldom exactly the same, but if the differences are large, it is important to try to figure out why. One reason for following directions carefully and for keeping records of one's work is to provide information on what might have caused the differences.

3A – Technology and Society

Measuring instruments can be used to gather accurate information for making scientific comparisons of objects and events and for designing and constructing things that will work properly.

4E – Energy Transformation

Some materials conduct heat much better than others. Poor conductors can reduce heat loss.

11A – Systems

In something that consists of many parts, the parts usually influence one another.

11B - Models

Seeing how a model works after changes are made to it may suggest how the real thing would work if the same were done to it.

12D – Communication Skills

Use numerical data in describing and comparing objects and events.

12E – Critical-Response Skills

Recognize when comparisons might not be fair because some conditions are not kept the same.

Seek better reasons for believing something than "Everybody knows that . . ." or "I just know" and discount such reasons when given by others.

Benchmarks (Grades 6 through 8)

1C – The Scientific Enterprise

Accurate record-keeping, openness, and replication are essential for maintaining an investigator's credibility with other scientists and society.

3A – Technology and Society

Technology is essential to science for such purposes as access to outer space and other remote locations, sample collection and treatment, measurement, data collection and storage, computation, and communication of information.

4F – Motion

Light from the sun is made up of a mixture of many different colors of light, even though to the eye the light looks almost white. Other things that give off or reflect light have a different mix of colors.

11A – Systems

A system can include processes as well as things.

Thinking about things as systems means looking for how every part relates to others. The output from one part of a system (which can include material, energy, or information) can become the input to other parts. Such feedback can serve to control what goes on in the system as a whole.

11B – Models

Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly, or that are too vast to be changed deliberately, or that are potentially dangerous.

12A – Values and Attitudes

Know that hypotheses are valuable, even if they turn out not to be true, if they lead to fruitful investigations.

12C – Manipulation and Observation

Read analog and digital meters on instruments used to make direct measurements of length, volume, weight, elapsed time, rates, and temperature, and choose appropriate units for reporting various magnitudes.

Benchmarks (Grades 9 through 12)

1A – The Scientific World View

Scientists assume that the universe is a vast single system in which the basic rules are the same everywhere. The rules may range from very simple to extremely complex, but scientists operate on the belief that the rules can be discovered by careful, systematic study.

1B – Scientific Inquiry

Investigations are conducted for different reasons, including to explore new phenomena, to check on previous results, to test how well a theory predicts, and to compare different theories.

National Standards (Grades 5-8)

Understandings about Scientific Inquiry

Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations.

Transfer of Energy

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.

Nature of Science

Scientists formulate and test their explanations of nature using observation, experiments, and theoretical and mathematical models. Although all scientific ideas are tentative and subject to change and improvement in principle, for most major ideas in science, there is much experimental and observational confirmation. Those ideas are not likely to change greatly in the future. Scientists do and have changed their ideas about nature when they encounter new experimental evidence that does not match their existing explanations.