The Reason for Seasons

activity 19 The Reason for Seasons BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade 4 Quarter 2 Activity 19 SC.E.1.2.1 The student knows that the tilt of the Earth on its own axis as it rotates and revolves around the Sun causes changes in season, length of day, and energy available. SC.E.1.2.3 The student knows that the Sun is a star and that its energy can be captured or concentrated to generate heat and light for work on Earth. SC.H.1.2.2 The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results. SC.H.1.2.3 The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H.1.2.4 The student knows that to compare and contrast observations and results is an essential skill in science. SC.H.1.2.5 The student knows that a model of something is different from the real thing, but can be used to learn something about the real thing. SC.H.2.2.1 The student knows that natural events are often predictable and logical. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 40 hands-on activities at this grade level. 1. Ask, What are some things that help you tell one season from another in Florida? (a calendar; slight changes in temperature; slight changes in weather conditions) Is Florida in the Northern or Southern Hemisphere of Earth? (northern, 23 degrees north latitude at the southern tip of Key West) How does this explain the annual temperature in southern Florida? (We are closer to the equator, and so receive more direct sunlight for longer periods of the year, and stay warmer overall.) If Earth did not have a tilt to its axis, who broward county hands-on science Quarter 2 211

would notice it more, a person in Florida, a person in Pennsylvania, or a person in Maine? (the person in Maine, because the less direct the sunlight, the colder the temperatures would be) 2. Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. 212 activity 19 The Reason for Seasons

activity 19 The Reason for Seasons OBJECTIVES Students model how sunlight strikes Earth as it revolves around the Sun and relate their observations to seasonal variations experienced on Earth. The students use a model to show the tilt of Earth s axis as it revolves around the Sun note that the intensity of sunlight striking Earth is stronger during the summer months than the winter months explain what causes seasons on Earth SCHEDULE About 40 minutes VOCABULARY equator Northern hemisphere season Southern hemisphere MATERIALS For each student 1 Activity Sheet 19, Parts A and B For the class 1 ball, plastic (for model) 1 base, plastic (for model) 2 batteries, D-cell 1 compass, magnetic 1 flashlight 2 foam sheets 6 index cards, 3 in. 5 in. 1 marker, black* 1 pc paper, plain* 1 ruler, metric 1 pair scissors* 1 straw, plastic 1 support rod (for model) 1 roll tape, masking DSR Solar System *provided by the teacher PREPARATION 1 2 3 4 5 6 Make a copy of Activity Sheet 19, Parts A and B, for each student. Put the batteries in the flashlight. Make sure the flashlight is working properly. To assemble the Earth model, run the support rod through the hole in the Earth ball a few times to widen the hole, then set the ball aside. The support rod represents Earth s tilted axis. The seam around the Earth ball represents the equator. Turn the plastic base upside down and insert the straight end of the support rod through the hole in the base. (You may have to sever the perforation.) Hook the angled end of the rod into the small indentation opposite the arrow on the base. This arrow shows the direction of the tilt of Earth s axis. Turn the base right side up and place it on a flat surface. Cut a 2.5-cm (1-in.) length of straw. Slide the straw all the way down the support rod. Gently slide the Earth ball over the support rod so that it rests on the straw. Wrap a small piece of tape around the exposed end of the rod. Cut a circle out of one piece of foam to represent the Sun. Cut a star shape out of the other piece of foam to represent the North Star. broward county hands-on science Quarter 2 213

Figure 19-1. The assembled Earth model. 7 support rod Earth straw base Place the materials on a table in the center of the room. Make sure there is enough space around the table for students to gather and observe the model (see Figure 19-2). Activity Sheet 19, Part A The Reasons for Seasons 1. Use the model to describe how the Sun s rays strike the Northern Hemisphere during each season. a. Summer: The rays strike the Northern Hemisphere at a direct angle. b. Autumn: The rays strike the Northern Hemisphere at a less direct angle. c. Winter: The rays strike the Northern Hemisphere at a low angle. d. Spring: The rays strike the Northern Hemisphere at an angle similar to autumn. 2. When it is summer in the Northern Hemisphere, what season is it in the Southern Hemisphere? Use the model to explain your answer. It is winter in the Southern Hemisphere. The model shows that when the Northern Hemisphere is tilted toward the Sun, the Southern Hemisphere is tilted away from the Sun. 3. Based on the model, why do we have the warmest temperatures in summer? We have the warmest temperatures in summer because the Sun s rays are more concentrated, so we receive more energy from the Sun. BACKGROUND INFORMATION Earth s axis is tilted at an angle of 23.5. As Earth revolves around the Sun, different areas are tilted either toward or away from the Sun. This tilt is responsible for seasonal changes experienced some places on Earth. The equator is an imaginary line that divides Earth into Northern and Southern Hemispheres. As Earth revolves around the Sun, each hemisphere experiences a different season. Activity Sheet 19, Part B The Reasons for Seasons 4. Draw a picture that shows the tilt of Earth s axis during each season. The Sun should be in the center of your picture. Label each season. Drawings should show the Northern Hemisphere tilted toward the Sun in summer and away from the Sun in winter. During spring and fall, neither hemisphere should be tilted toward the Sun. 214 The winter solstice occurs on December 21 or 22. At this time, the North Pole is tilted away from the Sun. The Northern Hemisphere receives less direct sunlight. This hemisphere experiences winter while the Southern Hemisphere experiences summer. The opposite occurs during the summer solstice, which occurs on June 21 or 22. At this time, the North Pole is tilted toward the Sun. The Northern Hemisphere receives more direct sunlight and experiences summer. The opposite is true of the Southern Hemisphere. activity 19 The Reason for Seasons

1 2 Guiding the Activity Begin by holding a discussion about the seasons. Ask, What season is it now? How is summer different than winter? Write the word season on the board. Explain that seasons are short-term weather conditions that repeat on a regular basis. Review the four seasons: spring, summer, autumn, and winter. Explain that students are going to use a model of Earth and the Sun to find out what causes the seasons. In this model, a flashlight will be used to represent sunlight hitting Earth. But before they use the model, they will experiment with the flashlight to see the different ways in which sunlight can strike Earth s surface. Gather students around a table. Place a piece of paper in the middle of the table. Have a student volunteer hold the flashlight about 5 cm (2 in.) above the paper. Make sure the student shines the light directly down onto the paper. Use the marker to draw a circle around the lit area. Next, have the student hold the flashlight at an angle from the same height above the paper. Draw an outline around the lit area. Ask, What difference do you see between the two lit areas? Additional Information Answers will vary. Students should describe differences in daylight hours, temperature, nature, and so on. You may need to darken the room in order to see the lit area clearly. The light beam created by the angled flashlight is more spread out. Point out that, the more spread out the beam, the less concentrated the energy from the flashlight. Explain that the flashlight represents the Sun and the paper represents Earth. Ask, In which case do you think the amount of energy absorbed by Earth is greater? Why? Explain that rays of sunlight that strike Earth directly are more concentrated, so they carry more energy and heat the surface more than slanted rays do. Students may suggest that the amount of energy absorbed by Earth is greater in the first case because the Sun shines more directly on Earth. broward county hands-on science Quarter 2 215

Guiding the Activity Additional Information 3 Place the cut piece of foam that represents the Sun in the middle of the table. Label it by writing Sun on half of an index card. Use the compass to locate north. Then place the cut piece of foam that represents the North Star on the northern end of the table. Label it by writing north on an index card. Place the Earth model about 30 cm (12 in.) away from the Sun. Point out that the support rod is tilted. Explain that the rod represents Earth s axis, which is tilted at an angle of 23.5. Align the Earth model with the North Star by pointing the arrow on the model base to the North Star. Explain that the arrow shows the direction of the tilt of Earth s axis. Remind students that Earth revolves, or travels around, the Sun. It makes one full trip in a year. As Earth moves around the Sun, the axis always points to the North Star. 4 Point out the seam around the middle of the model Earth. Write the word equator on the board. Tell students that the equator is an imaginary line that goes around the center of Earth, dividing the top half and the bottom half. You may choose to show students the equator on a classroom globe. 216 Write Northern Hemisphere and Southern Hemisphere on the board. Explain that the top half of Earth is called the Northern Hemisphere. The bottom half is called the Southern Hemisphere. Have students point out the location of both hemispheres on the Earth model. Tell students that they are going to use this model of Earth to find out how Earth s tilted axis causes seasons. activity 19 The Reason for Seasons Remind students that the United States is located in the Northern Hemisphere.

Guiding the Activity Additional Information 5 Darken the room. Have a student volunteer hold a lit flashlight horizontally above the Sun, shining the light on the equator of the Earth model. Ask, Which hemisphere of Earth receives more direct rays when the Sun and Earth are in this position? the Northern Hemisphere Remind students that when the Sun s rays strike Earth directly, Earth absorbs a lot of energy. Ask, Which season do you think it is in the Northern Hemisphere when the Sun and Earth are in this position? summer Have a student make an index card label for summer. Place the label near the Earth model. 6 Now have a student move the Earth model counterclockwise to a spot on the table that represents one-quarter of Earth s orbit around the Sun. The arrow on the base should point toward the North Star. Have a volunteer shine the flashlight on the equator. Ask, Which hemisphere is pointed toward the Sun? Help students see that neither hemisphere is pointed toward the Sun in this position. Tell students that this position represents autumn for the Northern Hemisphere. During autumn, both hemispheres experience 12 hours of daytime and 12 hours of nighttime. Have a student make a label for autumn and place it near the model. The spring equinox occurs on March 20 or 21, and the fall equinox occurs on September 22 or 23. 7 Continue the activity by having student volunteers move the Earth model through two more quarter revolutions representing winter and spring in the Northern Hemisphere. At each position, have students note the angle of the Sun s rays on the Northern Hemisphere. Have volunteers make labels for winter and spring, and place them in the proper positions on the table. A completed model is shown in Figure 19 2. Figure 19-2. The completed model. broward county hands-on science Quarter 2 217

8 Guiding the Activity Distribute a copy of Activity Sheet 19, Parts A and B, to each student. Have students complete the activity sheets in pairs. When students have completed their activity sheets, discuss how the model helped students learn about the seasons. Ask, What did the model show you that helped you understand what causes seasons on Earth? As appropriate, read or review pages 2 and 3 from the Delta Science Reader Solar System. Additional Information Students should say that the model showed them how sunlight hit Earth more directly in the summer and less directly in the winter. R EINFORCEMENT Have students discuss what seasons might be like if Earth s axis was not tilted. Students should realize that there would be little seasonal variation for most places throughout the year. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. C LEANUP Take apart the Earth model and store it, along with the pieces of foam and the compass in the kit. 218 activity 19 The Reason for Seasons

Connections Science Extension Ask the Venus team to report additional information they have found and to record Venus s data on the class master chart. Additional Facts about Venus Volume (Earth = 1): 0.86 Mass (Earth = 1): 0.815 Density (water = 1): 5.25 Surface temperature: 870 F (465 C) Composition: iron core, rocky mantle Distinctive features: brightest star in the sky, known as the Morning Star or Evening Star; carbon dioxide atmosphere produces extreme greenhouse effect, making Venus the hottest planet in the Solar System; surface temperature is hot enough to melt lead; volcanic lava flows; constant lightning in atmosphere Ask the Earth team to report additional information they have found and to record Earth s data on the class master chart. Additional Facts about Earth Volume: 1 Mass: 1 Density (water = 1): 5.52 Surface temperature: -94 F to +130 F (-70 C to +55 C) Composition: solid iron inner core, molten iron outer core, rocky mantle, rocky crust Distinctive features: only planet known to support life; unique combination of abundant water and oxygen/nitrogenbased atmosphere Ask the Pluto team to report additional information they have found and to record Pluto s data on the class master chart. Additional Facts about Pluto Volume (Earth = 1): 0.0066 Mass (Earth = 1): 0.0025 Density (water = 1): 2.0 Surface temperature: -364 F (-220 C) Composition: large rocky core, layer of water ice, layer of water and methane ice Name of moon: Charon Distinctive features: odd orbit overlaps Neptune s orbit, bringing Pluto closer than Neptune to the Sun twice each revolution Science and the Arts Obtain a copy of the children s book To Space and Back, astronaut Sally Ride s first-person account of her space-shuttle trips in orbit around Earth. Give students time to read the book, then ask them to work in teams to write and perform short skits dramatizing various scenes described in the book. Science and the Language Arts Tell students they can often infer the meanings of words if they know the meanings of common prefixes and suffixes. As an example, have them look up the meaning of the prefix eq-, found in the term equator. (eqmeans equal ) Then ask them to explain the meanings of other words they may be familiar with that contain the prefix eq-, such as equidistant. Science and Social Studies Encourage students to research the constellations and other sky myths developed by different cultures. For example, the Tsimshians, Native Americans of the Pacific Northwest, believed that the Sun whom they called The One Who Walks Over the Sky wears a flaming mask that lights Earth and creates stars with sparks blowing out of his mouth when he sleeps. broward county hands-on science Quarter 2 219

220 activity 19 The Reason for Seasons