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MUSE | Earth-Moon-Sun Dynamics | Course Overview and Materials | Building the EMS Model | Course Material 2F: Seasons | Instructional Notes

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INSTRUCTIONAL NOTES

Intended Learning Outcomes
• Create models to account for phenomena.

• Recognize data patterns.

• Assess models for data fit and consistency.

• Alter component of model and predict (cause to effect reasoning).

• Identify components of model.

• Use model to make prediction.

• Use classroom norms (basic and intermediate interpersonal skills).

• Make observations.

• Organize data.

• Make diagrams.

• Create graphs.

• Analyze graphical data.

• Use props to create or communicate model.

• Understand that models are ideas that scientists use to explain patterns they see in the world. In other words, models are explanations that scientists develop for natural phenomena.

• Understand that models are judged to be acceptable or not based on how well they explain the data, how consistent they are with other knowledge (or realistic), and how well they can be used to predict.

• Understand that seasons are caused by the tilt of the Earth (23.5°) and the Earth’s revolution around the Sun. Even though the Earth’s orbit around the Sun is slightly elliptical, the distance of the Earth from the Sun is NOT the cause of the seasons. (In fact, the Earth is closest to the Sun while the Northern Hemisphere is experiencing winter.)

• Understand that in the Northern Hemisphere, the Sun appears lower in the sky during the winter (is at its lowest noontime angular height on December 21), and higher in the sky during the summer (is at its highest noontime angular height on June 21).

• Understand that in winter in the Northern Hemisphere, the Sun appears to rise in the Southeast and set in the Southwest, and the day length is at its shortest. In summer, the Sun appears to rise in the Northeast and set in the Northwest, and the day length is at its longest.

• Understand that in winter the Sun’s rays are less direct.

• Understand that in summer the Sun’s rays are more direct.

• Understand that seasons are reversed in the Northern and Southern Hemispheres.

• Understand that the Sun is never directly overhead (at a 90° angular height) at any latitude further north than the Tropic of Cancer (23.5°N), or further South than the Tropic of Capricorn (23.5°S). Within the tropics (23.5°S-23.5°N) the sun is directly overhead two times each year.

Supplies
• Earth globes

• Light source (to represent the Sun)

• Sun Strip Activity from Project STAR

• Graph paper

• Calculators

• Sun Domes from Material 2B, each with three data curves – have one per group or one per pair of students

• Sun Domes (plotted by the teacher or reserved from last year's class), with curves for Spring/Fall, Summer, and Winter already plotted – have one per group if possible or one per classroom

Time Frame and Sequence

The Seasons (2F) Material will take 5-6 class periods to complete as described here. However, since this material comes toward the end of the EMS unit, we have noted a great deal of variety in the amount of time that teachers choose to spend studying this set of ideas. Some teachers find themselves pressed for time and complete the material more quickly than described here, while others choose to delve more deeply into the data with their students and require additional time to bring the material to a close. The Seasons Material is ideally suited to enrichment activities that allow students more hands-on data experiences, a wider range of data sources, etc. Thus, we recommend that you familiarize yourself with our Time Frame & Sequence with this built-in flexibility in mind. The resources, particularly the Project STAR materials, should provide a starting place for designing and/or choosing enrichment tasks related to seasons.

As described here, the students begin by brainstorming characteristics or phenomena that define different seasons. Next, they analyze local data and identify seasonal trends. After describing these trends for their own geographical location, the students analyze data from other cities globally and conclude with a description of global seasonal trends. Finally, the students add a component to their EMS model, the tilt of the Earth on its axis, in order to account for these seasonal phenomena.

Day 1

Pretest

Give students about 10 minutes to complete the Seasons Pretest prior to beginning the Seasons material.

Sun Strip Activity

The Sun Strip Activity can be found in the Project STAR textbook, The Universe in Your Hands, on pp. 54-56. Project STAR materials can be ordered online or by mail through Learning Technologies, Inc:

59 Walden Street
Cambridge, MA 12140
1-800-537-8703
www.starlab.com/psgi.html

During the Sun Strip Activity, students measure the diameter of the Sun as it appears from a set location on Earth at a set time of day during intervals that occur over a one year period. Next, they perform simple mathematical conversions to calculate the distance of the Earth from the Sun during each month of the year. Finally, they plot the Earth-Sun distance on a circular graph such that the Earth's orbital path is approximated by the graph. The important outcome of this activity is for students to realize that:

• The Earth's orbit around the Sun is very nearly circular and not extremely elliptical as many students believe.

• The Earth is actually farthest away from the Sun during the month of July (when the Northern Hemisphere is experiencing summer) and closest to the Sun during the month of January (when the Northern Hemisphere is experiencing winter).

• Therefore, the distance from Earth to the Sun is not the cause of global seasonal trends. For example, we can't explain why it is colder in winter (as opposed to summer) in the Northern Hemisphere by saying that the Earth is simply moving farther and farther away from the Sun during the months of November, December, and January. The data available to students through this activity disproves this model.

The learning outcomes above are addressed in the discussion questions that accompany the Sun Strip Activity. Assign these questions for homework on Day 1.

Day 2

Discussion of Sun Strip Activity

Begin class today by reviewing the students' answers to the Sun Strip Activity Discussion Questions. Remind them that their Seasons Pretest questions also dealt with their understanding about what causes seasons and the role that the Earth-Sun distance plays in this phenomenon (review Questions 1 and 4 from the pretest in particular). Use the bulleted learning outcomes listed above for Day 1 as a guide for summarizing this discussion.

Brainstorming

Ask students to return to their small research groups and hand out the brainstorm question. Give students about 10 minutes to brainstorm phenomena associated with different seasons in their small groups and then lead a class discussion to create a comprehensive list of their ideas. Post the list on the board or in some other prominent position in the room. Note aloud that the class has a lot of ideas about seasons and that during the next few days they will be modifying their EMS model to explain why places on Earth experience seasons the way that they do.

Looking for Patterns: Examining Sun Dome Data

Ask students what they have always begun with when attempting to create a scientific model. Students should answer that they have begun with data and seeking patterns in data. Remind them that they have been collecting data about the Sun's location in the sky throughout the unit (Material 1B: Sun Plot) by using their Sun Domes. Hand out a dome to each group or to each pair of students, depending upon your dome supply. At this point in the unit, each dome should have at least three curves representing the path of the Sun (including its angular height) on three different days. Ideally, these data sets should have been recorded approximately three weeks apart, in order for students to see the maximum amount of change from one curve to the next. Additionally, we recommend that you have on hand at least one dome (ideally one per group) on which three other curves are plotted: one for spring and/or fall, one for summer, and one for winter. You may plot these curves yourself or reserve domes that were plotted by students in previous years.

Tell students that their task is to describe all of the patterns that they notice by looking at the domes. Give them 10-15 minutes to work on this task and circulate throughout the groups during this time. Conduct a class discussion to summarize students' observations. Again, keep a class list of the data patterns in a prominent location. Patterns that should be apparent from the dome data are:

• Angular Height of the Sun: the Sun is highest in the sky in summer and lowest in winter. Fall and spring are intermediate.

• Direction of Sunrise and Sunset: sunrise direction progresses from North-of-East to South-of-East as summer turns into fall and then winter. Likewise, sunset direction progresses from North-of-West to South-of-West during this same time period.

• Day Length: the Sun is in the sky for a maximum number of hours during summer months and a minimum number of hours in winter. Spring and fall are intermediate.

Now return to the original class brainstorm list of phenomena associated with seasons. Make sure to add these phenomena if they are not already represented on the list. Tell the students that they are going to continue to look at several phenomena associated with seasons, but not all of the ones described on the list. For the next few days, the students will focus on the following phenomena:

• day length
• temperature (and precipitation)
• angular height of the Sun
• direction of sunrise and sunset

Day 3

Local Seasonal Trends

Begin today by reviewing the trends in the dome data that you noticed yesterday. Then, hand out a local data packet (ours is called the "Madpacket" and is specific for Madison, Wisconsin) to each student. In their small groups, students should study the data, note patterns, and complete the "Seasonal Characteristics Summary Chart" at the back of the packet. Point out that the summary chart should be a qualitative – not quantitative – description of seasonal phenomena. Once students have had sufficient time to complete their charts, ask for volunteers to share their ideas. Instruct students to take notes or modify their summary charts during this discussion such that each student has a personal copy of the chart and that the information reflects consensus ideas. A sample chart is available in the Samples of Student Work section of this material.

Next, hand each group one Global Data Packet. There are four different global packets available here, all for temperate cities in either the Northern or Southern Hemisphere:

Try to distribute the different city packets evenly throughout the class, with each group receiving only one packet. Also, it is helpful for future work if each student has her own copy of the group packet. For homework tonight, ask each student to locate her city on a globe or atlas and to compare this location to that of their own city.

Day 4

Global Seasonal Trends

Before beginning to work on the global data packets, ask for volunteers to show the class where each of the cities in the packet is located on a classroom globe. It is important for students to become oriented to the location of these cities relative to their own geographical location.

Remind students that their work with the Madpacket (or their own local packet) has provided them with a way of determining when it is summer or winter. For example, it is summer when the Sun is at its highest point in the sky and is in the sky for longest, etc. Using this information and the global data packets, ask the students to determine which are the summer and winter months for their assigned global city. After groups have had sufficient time to complete this task, ask students to turn to their "Seasonal Trends Around the World" chart and share group results in order to complete this entire chart. Once the chart is complete, you can note that the seasons are temporally reversed in the Northern and Southern Hemispheres (as determined by looking at several phenomena that define or describe seasons). A sample of one student's chart is available here.

Hand out a blank POM to each student. Ask students to fill in the question:

What causes seasons in the Northern and Southern Hemispheres?

Together, fill in the Phenomena column of the POM. Be sure to include the following phenomena:

• Northern Hemisphere experiences winter during December-February; summer during June-August.

• Southern Hemisphere experiences winter during June-August; winter during December-February.

• In BOTH hemispheres, the Sun is at its highest angular height and is in the sky for longest in the summer (and the opposite is true for winter).

• In BOTH hemispheres, temperatures are highest in the summer and lowest in the winter.

For the remainder of the class, each group should work to modify their EMS model to account for this set of phenomena that is associated with seasons.

Day 5

EMS Model

Ask the student groups to spend the first few minutes of class reviewing their work from yesterday. Next, assign each group one of the phenomena in the POM to explain in detail to the class. You are likely to have more groups than phenomena, but that is OK. You can either ask more than one group to focus on each phenomenon or choose to assign some groups extension questions instead. For example, you might ask one group to use their model to determine where on the Earth you must be in order to see the Sun directly overhead at any time during the year.

After the groups have had a chance to discuss their specific phenomena, ask each group to share their EMS model and explanation for their phenomenon with the entire class. You will probably want to begin with one of the following phenomena:

• Northern Hemisphere experiences winter during December-February; summer during June-August.

• Southern Hemisphere experiences winter during June-August; winter during December-February.

In order to explain either of these phenomena, students will have to add a characteristic to their EMS model: the tilt of Earth on its axis. Ask each group in turn to explain their phenomenon or challenge question using their EMS model and to demonstrate their explanations using appropriate props (globes, light source).

Once you have completed this task, ask the students to take out their POM charts for seasons and lead a group discussion for completing them. The POM should contain the following objects and motions:

 Objects: Earth Sun Motions: Earth orbits (revolves around) the Sun once every 12 months Earth is tilted on its axis relative to the plane of its orbit

Day 6

Polar and Equatorial Seasonal Trends

Note that this instruction is optional. Following the students' work on an EMS model that can account for seasonal trends in temperate areas globally, you may want to provide them with (or ask them to find) data for polar and/or equatorial regions. Such data is found on this site within the Challenge Questions (Material 3A) section. Our teachers have elected to introduce polar and equatorial phenomena in the context of challenging students to apply their model to account for novel situations. However, this choice has been made in part due to time constraints. Thus, you may choose to ask all of your students to wrestle with this problem similarly to the way in which they explained the data patterns in their local and global packets.

Summarizing the EMS Model

Hand out an EMS Model Summary Chart to each student. Now that they have used their model to account for several phenomena (Materials 2A through 2F), and before the EMS exam, it is a good time to formally summarize what they have learned. Give the students sufficient time to create a comprehensive summary of the components of the model and the phenomena that it can explain, either in their groups or as a whole class. This summary chart should be useful as students prepare for their exam and in applying their models during the Challenge Problems.

Student Ideas and Teaching Strategies

Day 1: Sun Strip Activity

Research (our own and that of others) has shown that many students and adults believe that the distance from the Earth to the Sun is the principle cause of seasonal phenomena. The Annenberg/CPB Math and Science sponsored project, A Private Universe Project, Teachers' Lab, includes a summary of research findings about students' misconceptions related to seasons and also specific suggestions for determining your own students' ideas.

Because so many students believe that the Earth's elliptical orbit brings the Earth and Sun closer together during summer months, the Project STAR Sun Strip activity provides very powerful counter-evidence for most students. The Sun Strip activity provides students with real data that refutes common misconceptions about the Earth-Sun distance and its role in causing seasonal phenomena. Depending upon your own time constraints and the availability of materials, you may choose to provide the transformed data (that is, the actual Earth-Sun distances in miles) or a graph of this data to your students directly rather than asking them to perform the calculations and graphing themselves. In either case, it is important for students to have access to the data and for the class discussion and/or homework questions to focus their attention on the implications of this data on their personal models to account for seasonal phenomena.

If you do choose to complete the Sun Strip activity as it is described in Project STAR, note that creating a circular graph is probably a new skill for most students. To assist them with the task, plot the first few points with them using an overhead projector. Be sure to instruct students to plot from the Sun to the Earth on the graph provided.

Day 2: Brainstorming

During this brainstorming activity, students are likely to offer the following observations related to seasons:

• temperature is colder in winter than in summer
• days are longer in summer
• the weather is different in the winter
• most rain falls in the spring & summer
• flowers bloom in spring and trees grow leaves

In our experience, it is less likely for students to describe patterns in shadow length, angular height of the Sun, or direction of sunrise and sunset. However, a close examination of the Sun Dome data should make these patterns obvious to students.

Examining Sun Dome Data

In Material 1B: Sun Plot, you began to gather data about the Sun's path in the sky. Over the course of the unit, you should have collected three separate day's worth of Sun path data, ideally about three weeks apart. After each day of data collection, the students should have drawn a smooth curve through the data points, extrapolating to the base of the dome on both ends of the curve. This process is explained in detail in the Instructional Notes section of Material 1B. Note, however, that many students have difficulty with extrapolation of the curve: rather than continue the curve along its defined path, many students will alter the slope of the curve and draw a sharp line connecting the final data point and the base of the dome directly below that point (almost perpendicular to the original curve). In order to determine the direction and time of sunrise and sunset, you will need to examine the place where each curve meets the dome base. Thus, it is important that the students have accurately extrapolated these curves.

This EMS unit is taught over roughly a nine week period. During that time, it is possible to see the curve representing the path of the Sun shift (when curves are plotted about 3 weeks apart), but students will not be able to see the extreme scenarios (summer solstice and winter solstice). Thus, we recommend that you have on hand at least one dome on which the Sun path is plotted for dates close to June 21st and December 21st. You may gather data and create this dome yourself, or alternatively, you may reserve a student dome from previous years.

It may be desirable to continue collecting data with the Sun domes even after the EMS unit is complete: you can ask students to collect data roughly once per month and make predictions about the trends they expect to see.

Day 3: Local Seasonal Trends

We recommend that you use the resource links here to create your own local data packet for this activity. Students are most familiar with the seasonal phenomena in their own geographical area, so it is best to begin there. After you have discussed seasons and begun to define them in terms of particular phenomenological trends, you can provide students with additional data from geographical locations of comparable latitude in both hemispheres. Finally, you may choose to provide data for the extremes of latitude: the polar and equatorial regions.

Because much of this data is numerical in nature, there is potential for integrating mathematics instruction. Students need skills in creating and/or interpreting graphs in order to discuss the conceptual model that explains seasons. Thus, you may choose to ask students to collect data, graph it, or just interpret the graphs, depending upon the learning outcomes you wish to emphasize in this set of activities.

Day 5: EMS Model

When students share their EMS model for seasons today, be sure to emphasize both proximal and ultimate causality in their explanations. For example, a student might correctly state that shadow length increases in Madison as summer progresses to winter because the Sun is at a less and less direct angle. This is an example of a proximal cause. However, there is also a cause of the Sun's changing angle: the orbit of the Earth around the Sun and the tilt of Earth on its axis. This is the ultimate cause of the shadow length phenomenon. The EMS model provides an explanation at the ultimate causal level for each of the phenomena in the students' data packets. You may have to prompt students to discuss the phenomena at this level.

One key aspect of understanding seasonal phenomena is understanding the energy effects of direct versus indirect sunlight. Most students will be able to visualize the Earth tipped toward the Sun and note that the Sun is hitting certain areas more directly than others. However, many students will fail to appreciate the consequences of this in terms of energy. One demonstration that we have found helpful involves the use of an overhead projector, a uniform grid drawn on transparency paper, and a globe.

1. First, place the transparency paper with the grid (about 2 cm squares) onto the overhead projector and project the grid onto a flat surface. Ask the students how much light is entering each square of the grid. Most students will agree that the amount of light is equal because the size of the grid squares is uniform and the brightness of the light appears uniform in each square.

2. Next, make sure to establish the connection between light and energy: light is a form of energy.

3. Now place a large globe between the projector and the screen such that the grid is being projected onto the curved surface of the globe. Note that some squares are smaller than others. Those squares on the most curved part of the globe (relative to the light source) will be the most elongated.

4. Ask the students to point out the area on the globe that is getting the most direct sunlight and be sure to note that these are the smallest squares on the grid and are near the equator (least curved portion of globe).

5. Then remind students that we have established that each square contains the same amount of light energy. Note that in some cases, when the light is hitting the globe indirectly, the energy is spread out over a much greater area than in cases where the light is direct.

6. Be sure that students understand the analogy between this demonstration and the way in which energy from the Sun is distributed over the curved surface of the Earth.

If time allows and your students seem prepared for it, you may want to ask them a few challenge questions related to seasons. For example:

• Is the Sun ever directly overhead in Madison, Wisconsin? If so, when?

• If the Earth were tipped 40° on its axis instead of 23.5°, would you expect winter days in Madison to be longer or shorter on average? Why?

• Where (and at what time of year) would you have to be on Earth in order to see the Sun directly overhead? Why?

• Alaska is sometimes referred to as "The Land of the Midnight Sun." This is because there are certain days during the year when the Sun never sets (goes below the horizon). During what time of year does this occur? Demonstrate this phenomenon using physical props.

Day 6: Polar and Equatorial Regions

The polar and equatorial data packets are included in Material 3A: Challenge Questions. You may choose to ask all of your students to explain these phenomena using their EMS model as part of the Seasons instruction, or you may choose to use these phenomena as sample challenge questions in the final material of the unit.

EMS Model Summary Chart

At the end of Material 2D: Moon Phases, the students completed an EMS Summary Chart. You may choose to ask them to take out that chart and complete it at this point or you may elect to hand out a new chart. There are many ways to alter this summary activity: students may work in class or at home, alone or in groups, etc. In any case, it has been helpful to provide some structure for a comprehensive summary of the phenomena that the EMS model can account for and the particular components of the model that are essential for explaining each of those phenomena. A sample summary chart is provided here.

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