National Institutes of Health
National Institute of Arthritis and Musculoskeletal and Skin Disorders
Main Getting Started Teacher's Guide Student Activities About NIH and NIAMS
Lesson 6 has two activities and will take two days to complete. In the first activity, students investigate the relationships between certain environmental factors and levels of exposure to sunlight. Students form hypotheses related to how variables such as location, time of year, time of day, and the weather influence the intensity of sunlight. They test their hypotheses using student- and teacher-generated results in an online database. In the second activity, students design and carry out experiments that test the effectiveness of various items intended to provide protection from the sun.
After completing this lesson, students will be able to
Consult the following sections in Information about the Musculoskeletal and Skin Systems:
Additional information about skin cancer can be found at http://cancer.gov/cancerinfo/types/Skin/ and http://www.mskcc.org/mskcc/html/420.cfm. General information about skin and skin problems can be found at http://www.aad.org/.
| Activity | Web Component? | Photocopies | Materials |
|---|---|---|---|
| 1 | Yes | Master 6.1, Calculating the Shadow Ratio, 1 transparency | SunCheck Timers (3 per class) Meter stick (1 per class) Object to cast shadow 2 large sheets of paper |
| 2 | No | Master 6.1, Calculating the Shadow Ratio, 1 copy per team of 3 or 4 (optional) | SunCheck Timers 2 or 3 kinds of sunscreen 2 or 3 kinds of sunglasses T-shirts of different colors Other materials depending on student investigations (see Preparation) |
Note to teachers: The fraction of sunlight that causes damage to the skin is called ultraviolet (UV) light. These activities require students to use disposable UV monitors to measure different levels of exposure to sunlight. The specific products recommended for this activity are sold as SunCheck Monitors and Timers. These products have three different UV-sensitive panels. Each panel is protected by a cover that you peel off before use. The three panels are designed to represent three types of skin sensitivity to UV light: normal, sensitive, and supersensitive. Exposure to sunlight causes the panels to turn from white to blue. When the color of the panel matches that of the reference panel, then the wearer is assumed to have been exposed to enough UV light for that day. In this lesson, we don’t regard the SunCheck products as tools that assess “safe” levels of sun exposure. Instead, they are simply used as inexpensive monitors of UV-light exposure.
To use the SunCheck Monitor or Timer,
SunCheck Monitors and Timers are available from a number of suppliers, including
Purchase SunCheck Timers for use in both activities. (Throughout the lesson, the two SunCheck products are collectively called SunCheck Timers.) The timers cost between $0.50 and $1.00 each, depending on the supplier and the quantity purchased. To make sure that SunCheck Timers are available for this lesson, remember to order them well in advance.
Note to teachers: In Activity 1, students use data obtained from SunCheck Timers to explore different factors that influence exposure to UV light. At the same time, students will encounter data about shadow ratios, where
shadow ratio = length of shadow / height of object casting the shadow
Before beginning this lesson, determine how much time is required for the supersensitive panel on a SunCheck Timer to match its reference color. To do this, take the SunCheck Timer outside (not indoors or behind glass), peel off the protective cover from the supersensitive panel, and place the timer in a location that is exposed to sunlight. You might want to tape the timer in place to prevent the wind from moving it. Ensure that the timer will remain in the sun for the entire exposure and that the location will not become shady. Write down the time the exposure begins and the time when the supersensitive panel matches its reference color. Also determine the shadow ratio when you first expose the timer. Measure the height of an object and the length of its shadow. A meter stick is handy for this task. Record the shadow ratio as the shadow length divided by the object height (see Master 6.1, Calculating the Shadow Ratio). You will need this information for the database used in Activity 1. The time it takes for the supersensitive panel to match its reference color can be less than 30 minutes during warmer months or an hour or more during winter months.
You will also need to collect data (shadow ratios and corresponding times of exposure using SunCheck Timers) at three different times of day. Begin taking measurements when the shadow is longer and will be getting shorter or when the shadow is very short and will be getting longer. For example, you could collect data at 8 a.m., 10 a.m., and 12 p.m., or 12 p.m., 2 p.m., and 4 p.m. These data could be collected on a weekend or by student volunteers during the week.
After you have three shadow ratios and three corresponding times for the supersensitive panel to match its reference color, go to the Web site http://science.education.nih.gov/supplements/bone/student. Under "Teacher Administration," click on “Lesson 6—Database.”
The database includes only times corresponding to the supersensitive panel. The factors that influence these times also work in the same way to influence times for the other two panels. We suggest using the times for only the supersensitive panel because they are the shortest and therefore the easiest to measure. Depending on conditions, the exposure time needed for the normal panel to match its reference can exceed four hours. Using the sensitive and normal panels is optional, but only times corresponding to the supersensitive panel should be entered in the database.
Have an adequate number of SunCheck Timers and meter sticks on hand. Also have available two or three sunscreens with different SPFs, two or three different types of sunglasses, and some different articles of clothing, such as T-shirts of different colors. To make this easier, you can ask student volunteers to bring these items to class before the lesson.
Prepare photocopies and transparencies.
Note to teachers: This lesson discusses the benefits and risks associated with exposure to sunlight. For the most part, we’re referring to the ultraviolet part of the light spectrum. If your students are familiar with the light spectrum, you may want to speak of UV light rather than sunlight.
Student responses will vary. Some may feel that sunlight is good for health because they associate it with an active lifestyle. You may follow up such a response by asking, “Are people who spend a lot of time outdoors healthy because of exposure to the sun or because they get lots of exercise?” Some students may mention that sunlight is needed to help the body produce vitamin D. Other students may respond that sunlight is bad for one’s health because it can lead to sunburn, skin damage, and increased risk for getting skin cancer.
Students should understand that a healthy relationship with sunlight involves a balance between its health benefits and risks. Students may focus on how they would like their skin to look in order for them to “fit in” rather than how to keep their skin and bodies healthy. Explain to students that the National Institutes of Health (NIH) recommends that “the best skin color is the one you were born with.”
Note to teachers: Some students may believe that dark-skinned individuals do not get sunburned and are not at risk for skin cancer. However, dark-skinned individuals do get sunburned and may be at a significant risk for sun-induced skin cancer. Recent research has demonstrated that complex factors, such as skin type, genetics, and melanin distribution, may be as important as race and skin color in determining skin-cancer risk.
In dark-skinned individuals, melanin production is continuous. In light-skinned individuals, exposure to UV light stimulates the production of melanin. Melanin absorbs UV light and provides some protection against the damaging effects of UV light. The skin becomes darker (it tans) as melanin levels increase to protect the skin from UV exposure. A suntan or sunburn actually represents cellular damage from UV exposure. Importantly, UV light causes damage to DNA. The UV light used in tanning booths is no different and increases the risk for getting skin cancer and premature aging of the skin.
Student responses will vary. Make sure that the following are mentioned:
Students are unlikely to be familiar with techniques for measuring UV light. A few students might be familiar with products that change color in response to UV light, the UV index, or UV meters.
You will add the SunCheck times to the paper in Step 8. The paper should look similar to the following:

Figure 6.2. Data collection setup.
Tip from the field test: The SunCheck Timers’ three panels are designated “supersensitive,” “sensitive,” and “normal.” These refer not to skin types but to different sensitivities to the sun. In this activity, the SunCheck Timers are simply used as inexpensive UV monitors. Despite what the packaging materials may say, students should not think of them as tools for assessing safe levels of UV exposure. Refer to the teacher note after this activity’s Step 2.
Display the paper with the shadow ratios and times for the SunCheck Timers. Students will use this information in Activity 2: Be Prepared!
Students have a number of options for generating average exposure times in the database, such as average exposure times for specific
The database allows students to formulate and test many different questions by comparing average exposure times for various environments. For example, questions that can be tested by using information in the database include the following:
Students are limited by their imaginations, but their questions must be answerable using the available data.
At the middle school level, converting the question to a statement is an acceptable method for establishing a hypothesis. For the example question, “Are times longer during winter months and shorter during spring months?” a hypothesis can be, “Times during winter months are longer than times during spring months.” Students could then test this hypothesis by comparing the average time during December with the average time during April. The alternative hypothesis, “Times during winter months are similar to times during spring months,” is equally acceptable.
A hypothesis is a statement that predicts an outcome. Hypotheses are testable. The statement is tentative because empirical evidence has not yet been obtained to support or contradict it. However, it is a reasonable statement, because it is based on prior knowledge about the phenomenon. For example, some students may have experienced that the sun is less direct during winter compared with spring. For these students, a reasonable hypothesis would be the first one suggested. Other students may live at lower latitudes and may experience similar amounts of sunlight during different months of the year. For these students, the second hypothesis is a reasonable one.
The validity of either hypothesis is tested using data. The data will either support or not support the hypothesis. Many students think that a good hypothesis is one that the data support. In fact, neither hypothesis (one that the data support or one that the data fail to support) is better. The important point is that students will have engaged in an authentic scientific activity. They will have formulated a hypothesis and used data to determine whether the hypothesis is supported or not supported. Using empirical evidence to draw conclusions about phenomena is a key feature of scientific inquiry.
To test a hypothesis, such as times are shorter during winter than during summer, a student has to generate two different reports, one for the winter and a second for the summer, and compare them. If possible, allow students to print their reports. Otherwise, instruct students to record the results of their reports on a piece of paper. If time allows, encourage students to ask additional questions and produce the reports necessary to answer those questions.
Note to teachers: The database will not accept an entry if a hypothesis is not entered. Testing some hypotheses will require that students generate more than one report.
Note to teachers: The following information is provided to assist you in answering students’ questions:
The reports should indicate whether the data supported or did not support the hypothesis and what evidence was used to form a conclusion.
Make sure that students are testing hypotheses that can be investigated using available data.
Even if the team has written an appropriate hypothesis, there may be too few entries in the database to reach a firm conclusion.
Group the shadow ratios and times for locations with similar latitudes and altitudes. Students should notice that the shadow ratio is smaller when the times are shorter. Keep the results posted in the classroom. Students may refer to these results during Activity 2.
Students should explain that latitude, elevation, time of year, time of day, and weather conditions can all affect the amount of UV light.
If students are uncertain how to respond, suggest that they consider different types of environments such as in and out of the shade or in and out of the water. If not mentioned by a student, bring up the topic of products designed to protect us from sunlight, such as sunscreens, sunglasses, and different types and colors of clothing.
To ensure that the class addresses a variety of questions, you may want to refer to the questions written on the board and have different teams volunteer to answer different questions.
Note to teachers: The SunCheck Timers will work when underwater or when covered with sunscreen.
Note to teachers: Make sure that the teams understand that a proper investigation should include a control where the timer is exposed to sunlight without protection. If necessary, take one question as an example and, in front of the class, go over how to design the investigation for that question. Teams should record the question, the hypothesis, and the design of the investigation on a piece of paper. They can refer to this while they conduct their investigations and again when they write a report of the investigation.
Students should use the data you collected to make their predictions.
Students should predict that the control timer will have a time similar to the results you obtained. Timers with sun protection such as shade, clothing, or sunscreen should have longer times. For example, students might predict that a SunCheck Timer placed next to the water will have a shorter time than the control.
If necessary, distribute copies of Master 6.1, Calculating the Shadow Ratio, to each team to help them determine the shadow ratio. Students should write down the time required for the panel that corresponds to supersensitive skin to match its reference color. The time needed to complete the investigations likely will go beyond class time. The time required to reach the maximum safe sun exposure does not have to correspond with your class schedule. If long times are being measured, students from other classes may check the timers. Another option is to have a student expose the timers over the weekend and record the times.
Note to teachers: To conserve the SunCheck Timers, you can use just one as a control for all experiments performed at the same time.
If any teams were not able to answer their questions, ask them what additional data they would need to do so. If teams draw conclusions that go beyond their data, guide the discussion to bring this out.
The shadow rule is an easy way for anyone to minimize the risks of sun exposure by staying out of the sun when UV light is more intense. Students will not usually have a SunCheck Timer with them, but they can notice how long their shadow is compared with their height.
Note to teachers: More information about the shadow rule is available in an article by T. Downham (see the Reference section, number 18).
Students should explain that the shadow rule directs them to seek shade when they have a short shadow. They should understand that shadows indicate how much UV light is present. They should also explain that when shadows are short, people should protect their skin from the sun by seeking shade or using products such as sunscreen, sunglasses, hats, and other articles of clothing.
| Activity 1: Measuring Sunlight | |
|---|---|
| What the Teacher Does | Procedure Reference |
Ask students, “Is sunlight good for your health?” |
Step 1 |
Explain the following information about UV light, which is one part of sunlight:
|
Step 2 |
Ask students whether they think the amount of UV light is the same during the summer and the winter. Ask students,
|
Step 3 and 4 |
Display a transparency of Master 6.1, Calculating the Shadow Ratio.
|
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Write “Time of Day,” “Shadow Ratio,” and “SunCheck Time” on a large sheet of paper. Record on the paper
|
Step 6 |
Pass around a SunCheck Timer and explain how it works.
|
Steps 7 and 8 |
Explain that you have entered the shadow ratios and the times for the supersensitive panel into a database and that they will use the database to develop a question about sunlight exposure.
|
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Instruct each team to ask at least one question that can be answered using the information in the database.
|
Steps 11–13 |
Instruct teams to write a summary of their findings. |
Step 14 |
Ask for volunteers to report their findings and explain whether the data supported their hypothesis.
|
Steps 15–17 |
Facilitate a class discussion of the relationship between the shadow ratio and the length of time for a supersensitive panel to match its reference color.
|
Step 18 |
As a homework assignment, ask students to write two or three sentences describing what influences the amount of UV light to which they are exposed. |
Step 19 |
| Activity 2: Be Prepared! | |
| What the Teacher Does | Procedure Reference |
Ask the class, “How you could protect yourself from too much sun exposure?” |
Step 1 |
Divide the class into teams of three or four.
|
Step 2 |
Ask each team to establish a hypothesis based on its question.
|
Steps 3 and 4 |
Once you have approved each team’s design, remind students that the shadow ratio can be used to assess the intensity of UV light.
|
Step 5 |
Ask students to predict what the time for each of their SunCheck Timers will be. |
Step 6 |
Distribute SunCheck Timers and materials needed to complete the investigations.
|
Step 7 |
Instruct teams to write reports of their investigations on a single sheet of paper.
|
Steps 8 and 9 |
Ask a few teams to compare their predictions with the shadow ratios and times they obtained in their investigations. |
Step 10 |
Ask students whether they think the shadow ratio is a good indicator of how much UV light they are getting. Explain that
|
Step 11 |
As a homework assignment, ask students to write a short paragraph describing
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Step 12 |