4 Light and shadows: The Sun moves in the sky
In this lesson, the class records observations of the Sun’s apparent motion or path through the daytime sky. Students will use landmarks as a basis for their recordings and to help make predictions about the Sun’s changing position. This activity should be repeated three times during different seasons.
After this activity, students should be able to:
- Describe the shape of the Sun’s path
- Describe the Sun’s movement and its relation to other objects each hour
- Use landmarks to record and make predictions about the Sun’s changing position
- Compare observations and recordings of the Sun’s path during each season
- Understand that the Sun rises in the east and sets in the west
- Predict where the Sun is before they arrive at and after they leave school
Classroom time required
- 40-minute introductory lesson held indoors
- 50-minute lesson held outside with 15 minutes every hour that day for small group recordings
The teacher will need the following:
- Digital camera to produce a panoramic photo of the southern horizon
- Panoramic photo of the southern horizon, enlarged to 7-foot × 3-foot
- Clear tape
- 9 circles with a 2-inch diameter cut from yellow construction paper
- A large stone, a flag, or some object to mark the area where the class will record data about the Sun’s path
- An observation site with an excellent view of the southern horizon
Each student will need:
- A panoramic photo of the southern horizon
Teacher background information
The apparent motion of the Sun across the sky from east to west, as well as the similar motion of all celestial objects, is explained as a result of the motion of Earth — and us with it. As we shall see later, the actual path of the Sun’s apparent motion reflects a complex interplay of Earth’s rotation, the resultant change in our orientation depending upon our latitude, and the position of Earth in its orbit.
The purpose of this lesson is to create a foundation of concrete observations common to the entire class. This lesson is an excellent opportunity to introduce the importance of careful, systematic observation and of presenting results in a clear and accurate way. It also invites students to realize that underlying our ability to comprehend nature is the fact that our observations reveal repeating, predictable patterns. In essence, science is the process of discerning, describing, and explaining these patterns.
There is a point, on which educated adults have been known to be unclear, that will probably come up at some point in this unit. We typically describe the apparent motion of the Sun as a result of Earth’s spinning motion about its axis. The idea that the Sun is in fact moving around Earth, it is thought, was overthrown by the Copernican revolution of the seventeenth century. This is, in fact, false. Indeed, all of our observations suggest Earth is spinning about its axis, completing one rotation every twenty-four hours or so. These observations include the apparent motion, not only of the Sun, but also of all other celestial objects — essentially anything in the universe that is not on Earth.
One could, without contradicting observations, say that Earth is not spinning. But one then has to claim that the entire universe is in fact spinning about Earth as a center. One also has to posit some rather unnatural causes for the (weak, but certainly measurable) centrifugal forces that we ascribe to our motion as Earth rotates. Most unnaturally, one will note that all the other planets in the solar system, and indeed all other celestial bodies, rotate about their own axis in addition to their apparent motion about Earth. It is thus far more natural to assume Earth is also in constant rotation about its axis. But fundamentally, taking the point of view of an Earth-bound person, describing the universe as revolving around Earth, is consistent if not simple.
The revolution engendered by Copernicus was not associated to this question at all. Instead, it addressed the fact that planets appear to be moving relative to the stars, in addition to the apparent uniform motion of everything that is explained by Earth’s rotation. This motion of the planets is far slower than the daily rotation of the entire sky, taking months or years to complete a cycle, depending on the planet in question. Before Copernicus, these apparent motions of the planets relative to the stars were explained by having planets move along complicated trajectories about Earth (epicycles). Copernicus showed that the same apparent motion resulted from far simpler, essentially circular, motion of the planets around the Sun, provided we allow that we observe this from an Earth, which itself orbits the Sun. The complicated apparent motions are the result of viewing simple motion from a moving platform. One can maintain the point of view of a stationary Earth even after Copernicus, at the cost of having the entire universe perform a yearly compensating motion, but the level of complexity involved in this choice becomes so high that it is rarely attempted by scientists.
The following list includes tasks the teacher should complete before beginning this lesson.
- Find a location on your school’s campus to view the southern horizon. Mark the spot with a rock, a flag, or some other semi-permanent object. Place a compass down and snap a panoramic photo facing due south. Print out a copy of the panoramic photo for each student. Have the photo enlarged and printed with an ideal size of about 7-foot × 3-foot for the entire class. Post the enlarged copy of the horizon up in your room.
- Take the time to familiarize yourself with the panoramic photo and to identify some landmarks or other features as they appear in the photo and in the actual view from the selected point. This will be helpful in explaining to students how the photo represents the actual horizon and how to relate positions in the photo to directions in the sky.
- Cut out nine yellow construction paper circles of an appropriate size to match the Sun’s apparent size on the scale of your enlarged photo. For a 7-foot × 3-foot photo, the circles should be about two inches in diameter. Write the date and an hour time on each (9/22 9 a.m., 9/22 10 a.m., and so on) for every hour students will be in class.
- Make a list of Sun Tracker groups with 4–5 students per group. Post in the classroom.
Have students discuss, write, and illustrate their understanding of any patterns they’ve noticed in the Sun’s path in the sky prior to this activity. Any interpretation of why the Sun appears to move across the sky and previous knowledge of east, west, north and south is not necessary.
- Introduce the activity with the following challenge.
A kindergartner at our school needs your help! The kindergartner came running home off the bus from school extremely worried and very upset. His mother met him in the kitchen, and asked, “What’s happened?” He explained, “When I left for school today the Sun was next to the big pine tree and when I just got off the bus at the end of the day, the Sun wasn’t there anymore. I’m afraid it’s lost. And I’m worried because I don’t know where it went and if it will ever come back!” Should the kindergartner be so upset? How can you help this kindergartner understand what really happened to the Sun?
- Hand out the panoramic photos and explain the photo’s view is on the school’s campus. Describe how they will us this photo to help the kindergartner solve the mystery described above.
- What things do you know that could help you answer the kindergartner’s questions?
- What things do you need to know to answer the questions?
Allow small groups to brainstorm for five minutes. Students should record their group’s ideas in their science notebooks. Illustrations with captions are encouraged to explain their responses. Have each group share their ideas and record them on chart paper for the class to view.
- Label and categorize the students’ responses into three categories: Sun information, Earth information, and light information. Ask students for feedback about how each response should be categorized.
- Before going outside, teach your students how to label at least three landmarks. Students should label their individual photos with the following:
- three landmarks
If necessary, the class can record the definitions of each term in their science notebook glossary sections.
- Teach students how to use their fists to count up from the horizon. Starting at the horizon below the Sun, place one fist on top of another until you reach the Sun, counting as you go up. Students mark the position of the Sun on their photo sheet using the width of their index finger to represent the distance of one fist, i.e. three fists is equivalent to three index fingers. Outside they will label the Sun with a small circle and note the time above it. Stress to your students never to look directly at the Sun. It can cause permanent eye damage.
- Take your entire class out to the marked spot facing the southern horizon. Students should have a pencil and their photos of the horizon labeled and taped in their notebooks.
Ask, “Did anyone see where the Sun was this morning on the way to school?” Determine the direction of east and a nearby landmark on the horizon. Everyone should label this area “sunrise.”
Ask, “Does anyone know what direction or position the Sun is in at the end of the day when you are going home from school or close to dinner time?” Label this area “sunset.” Label any additional landmarks that are important (trees, buildings, etc.).
Have students point and face due south and north and check to see if they have labeled their photos correctly.
- Ask, “How can you tell where the Sun is in the sky without looking at it? What clues give you hints about the Sun’s position?” Possible answers include the position of shadows and feeling the light on a certain side of your face. A somewhat more precise method is to hold the hand up so that it obscures the Sun completely. It is then possible to safely look at the hand, which is now in the same direction as the Sun, and measure its direction relative to the horizon, landmarks, etc.
- Without looking at the Sun, remind students how to identify the landmark on the horizon that the Sun is above. Use fists to count up from the horizon. Starting at the horizon below the Sun, place one fist on top of another until you reach the Sun, counting as you go up. Remember to warn the class not to look directly at the Sun as it can cause permanent eye damage. Students mark the position of the Sun on their photos using the width of their index finger to represent the distance of one fist. Label the Sun with a small circle and note the time above it. Ask, “Where will the Sun be in an hour? Why?”
- Return to the classroom and have a student place a yellow construction paper Sun on the enlarged horizon photo to represent where he recorded it on his personal photo. Ask the class, “Where will the Sun be in an hour? Why?” Have someone place a Sun in the predicted position.
- Each hour for the rest of the school day, have a Sun Trackers group of 4–5 students go to the observation location. Each group will measure the position of the Sun and record it on their photos. When the group returns to the class, they should move the predicted Sun to the position they observed and recorded. Lastly, they place a new Sun where they think it will be in an hour. This process continues every hour for the rest of the school day.
- At the end of the day or the beginning of the next day, review the enlarged photo and student recordings. The entire class should copy all of the times recorded by each group on the panoramic photo on the photos in their science notebooks.
Ask the class:
- What shape is the Sun’s path? What shape is this similar to? (i.e. rainbow, a ball thrown up that comes down, etc.)
- Where does the Sun go after you leave school?
- Next, have a volunteer make predictions about the Sun’s path during the next several hours. Allow small student groups to examine the photos for clues that will help them explain to the kindergartner what happened to the Sun. Have small groups make lists of five pieces of information that their recordings tell them about the Sun’s path, Earth, and light. Discuss the questions listed in Assessment section.
- Complete the Post-Assessment Activity in the Assessment section.
The pre-assessment for this lesson includes labeling the panoramic photos in the science notebooks.
The activity assessment for this lesson consists of the panoramic photo data recordings in the science notebooks and answers to the following questions. These questions are included in the following student worksheet.
- Assessment activity
- Activity assessment
- Open as PDF (12 KB, 2 pages; also available as Microsoft Word document)
- If you were to draw the Sun at six o’clock tonight, where would it be?
- Where would the Sun’s position be at midnight?
- Can you count on the Sun to be in the same positions tomorrow? In three months? In a year? Explain why or why not.
- What will the position of the Sun in the sky tell you about the time of day?
- Why do you think they call noon “the middle of the day” or the “midpoint of the day?”
- How will daylight savings affect our recordings?
- How does the Sun’s path in winter compare with the Sun’s path in fall?
- How or why do you think the Sun’s path affects or controls our town’s weather? Or how late you get to play outside after school?
For the post-activity assessment students should draw a model of the Sun’s path either by hand or using graphics software (such as KidPix) to illustrate and answer the following objectives and questions. A student worksheet containing the following directions and questions is provided below.
- Post-activity assessment
- Activity assessment
- Open as PDF (12 KB, 2 pages; also available as Microsoft Word document)
- Draw the southern horizon. Label it with east, south, west and at least four landmarks.
- Illustrate the Sun’s path as it changes position each hour.
- Describe the shape of the Sun’s path. What is the shape similar to?
- What do you notice about the pattern of the Sun’s path each hour?
- What happens to the Sun after it sets? Why can’t we see it?
- Some people say the Sun’s path across the sky is not a real motion. The Sun appears to us to move because Earth is spinning and we are spinning with it. Do your observations agree with this idea? Do they contradict it? What observations could you use to try to prove each of the two hypotheses?
Daily sunrise and sunset times
Recording the daily sunrise and sunset times is a wonderful everyday morning activity. Each day a student or you can research the sunrise and sunset times from the local paper or website. Chart the times to display patterns. Additionally, you can chart the high temperature of the day and see if students discover any patterns. This data can be graphed and interpreted to better understand the Sun’s path.
Track the Sun’s movement by measuring a stick’s shadow each hour. Each hour have a group track the stick’s size, shape, and direction. Check out This is a Stickup!, a great lesson that helps students record the smooth-arced motion of the Sun across the southern horizon.
The Sun’s path in the Southern Hemisphere
Present students with a diagram or animation of the Sun’s path in the Southern Hemisphere. Challenge them to compare this with their own observations. The Sun’s path in the Southern Hemisphere is reversed relative to our observations — the Sun appears to move from right to left. This challenge will likely puzzle students and keep them guessing; a promise that more will be explained later will build excitement and curiosity.
Warn students never to look directly at the Sun. Even a glance can cause permanent eye damage.
- the line where the sky and the Earth appear to meet
- east, west, north, south
- the four cardinal directions on a compass
- the shape of half a circle
- the vertical height of an object above some chosen level, especially above sea level (elevation); in astronomy, the angular distance of a celestial body from the horizon measured along the vertical circle passing through the body
- an identifiable, readily-visible object in a landscape, used as a reference point for describing other locations
- North Carolina Essential Standards
- Science (2010)
- 3.E.1 Recognize the major components and patterns observed in the earth/moon/sun system. 3.E.1.1 Recognize that the earth is part of a system called the solar system that includes the sun (a star), planets, and many moons and the earth is the third planet...
- Science (2010)
North Carolina curriculum alignment
- Goal 3: Geometry - The learner will recognize and use basic geometric properties of two- and three-dimensional figures.
- Objective 3.01: Use appropriate vocabulary to compare, describe, and classify two- and three-dimensional figures.
- Goal 3: The learner will make observations and use appropriate technology to build an understanding of the earth/moon/sun system.
- Objective 3.01: Observe that light travels in a straight line until it strikes an object and is reflected and/or absorbed.
- Objective 3.02: Observe that objects in the sky have patterns of movement including:
- Objective 3.03: Using shadows, follow and record the apparent movement of the sun in the sky during the day.