Shadows

[|Shadows Video]
** CE12 Shadows **
 * Unit of Study:** Changing Earth


 * Lesson Title:** Shadows

· How does the study of properties and patterns help us to understand the natural world? · How can we collect and analyze data to identify sequences and predict patterns of change within the Sun, Earth, and Moon system.
 * Essential Question(s):**

4.1A Demonstrate safe practices and the use of safety equipment as described in the Texas Safety Standards during classroom and outdoor investigations. 4.2B Collect and record data by observing and measuring, using the metric system, and using descriptive words and numerals such as labeled drawings, writing, and concept maps. 4.3A In all fields of science, analyze, evaluate, and critique scientific explanations by empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. 4.8C Collect and analyze data to identify sequences and predict patterns of change in shadows, tides, seasons, and the observable appearance of the Moon over time.
 * TEKS:**


 * Learning objective:** The students will understand that the Earth/Sun system creates a pattern in shadows over time. Students identify patterns in the shadows and discuss using content-based vocabulary how shadows are caused by changes in the position of the Sun across the sky.


 * Evidence:** Data collected, reflection questions and class/group discussion.


 * Pre-assessment:** The students will journal their answers to these reflective questions: How is a shadow created? Are shadows always the same size? Why or why not? Explain your answer.

1. Ask students, Are there any other patterns, other than the phases of the Moon, that can be observed deepen our understanding of the natural world? Explain to students that today they will observe shadows. 2. Each student will turn the paper plate upside down and write the letter N on one edge of the plate to mark the side that should face north. 3. With the plate still turned upside down, make a very small hole in the **center** using the tip of a pencil. Push the coffee stirrer through the plate about one-half to one inch. Put the plate back on the table. The stirrer should stand straight up. (Perpendicular to the plate) Use, tape if necessary to hold the stirrer straight up from the plate. 4. Create a chart in the science notebooks (see #7) to record the data collected during the experiment. **Note: The class will need at least 35 minutes outside to do the following investigation.** 5. Take the plate outside and place it in a sunny spot. The best location is best on a smooth surface such as concrete. Make sure the student is not casting a shadow over the plate. 6. Using a compass, position the plate so that the N is facing north. Tape the plate down. It is very important that the plate does not move during the investigation. 7. Make sure all of the students are ready to mark the shadow. Using a pencil, carefully trace the line created by the shadow of the coffee stirrer on the plate and label the time at the tip of the shadow mark. Tell the students the time, or they may use a watch. (add AM or PM to the chart) || 8. While waiting during the next 8 minutes to mark the shadow, have the students carefully measure the length of the shadow in cm using a decimal: 3.6cm. Or measure the length of the shadow in mm: 36mm. 9. Exactly 8 minutes later, trace the shadow of the coffee stirrer again and write the time at the end of the shadow. Record the length and time in the science notebook. Repeat again in 8 minutes. 10. Have the students put a pencil dot where they think the tip of the shadow will be at the end of the next 8 minutes. Fill in the chart for the prediction. While waiting, the students will write their reasons for the prediction in the science notebooks. 11. At the end of the 8 minutes, have the students trace the shadow of the coffee stirrer and write the time at the end of the shadow. Fill in the chart for the actual length. Discuss with a partner why you predicted the location you chose. Was your prediction the same as the actual reading? Why or why not? Where would your next prediction be and why? **Note**: During the time intervals, challenge the students to think and discuss the following questions, What happens to shadows as the position of the sun changes across the sky? Why does the sun appear to move across the sky during the day? //The Earth rotates counterclockwise from west to east throughout the day which makes the Sun look like it is moving, however it’s the Earth that is moving.// Is there a pattern to the sizes of shadows made by the sun? When are shadows outside the largest? //Shadows are// //longest in the morning and evening.// When are they the smallest? //Shadows are shortest at mid-day.// Can we always see shadows outside? //Usually not on a cloudy day or at night when there is no Sun present to produce a shadow. Other light sources may create shadows during the night.// · Challenge students to consider whether there is a pattern in the positions of shadows over the course of a day. Do shadows stay in the same place all day? //They become shorter as the morning becomes mid-day and they become longer as mid-day becomes evening. The shadow also changes position moving from west to east.//
 * Procedure:**
 * SAFETY: Remind the students never look directly at the Sun.**
 * Record || Length of Shadow || Time
 * 1st ||  ||   ||
 * 2nd ||  ||   ||
 * 3rd ||  ||   ||
 * Prediction ||  ||   ||
 * Actual ||  ||   ||

· Explore the area around the school flag pole to observe how shadows can be used to mark time. · Have the students work in pairs. · Provide the student with a copy of the chart to tape or glue in the science notebook. · Provide assistance in using and/or reading the ruler correctly. · Allow the student to create a sundial and check its accuracy throughout a morning, noon and afternoon time period. (See Shifting Shadows under references.) · Write the date on the sundial. Do the investigation every four weeks during the school year.
 * Considerations for differentiation:**


 * Materials per pair:** 1 paper plate, 1 metric ruler**,** 1 coffee stirrer, 1 directional compass, 1 roll of masking tape**,** science notebook

While students are aware that day and night occur, they may not yet understand that these changes happen because the Earth rotates once every twenty-four hours. Day occurs when our side of the Earth faces the Sun and night occurs when our part faces away. As the day progresses, the Sun appears to follow a path from its rising in the east to its setting in the west. It might seem that the Sun is moving across the sky, but we are really the ones who moved! We now know, of course, that the sun does not move across the sky as it appears. Rather, the Earth rotates as it revolves around the sun. One of the earliest ways of measuring time used the predictable changes in shadows that occurred as the sun moved across the sky. As the Sun rises, the shadows are long and point more towards the northwest direction in the United States. As the day progresses, the Sun’s location becomes higher in the sky causing a shorter shadow. As the Sun becomes lower in the evening sky, the shadow becomes longer and point towards the northeast direction. Since shadows change predictably over the course of each day, they can be used to estimate time. A stick placed vertically in the ground probably was the first sundial. Simple sundials were used to tell time in Egypt more than3,000 years ago. In early times, an hour was calculated as 1/12 of the period of daylight. Thus, depending on the time of year, the length of the hours in the day varied. Now, we divide each day into 24 equal hours, which remain unchanged regardless of the time of year. Today, time is also standardized from place to place. Before 1884, every locality set its clocks to the highest position of the sun (=noon). This led to considerable confusion, because every town ran on a different time. Now, the world is sectioned into 24 standard time zones that are uniform. Each time zone accounts for 15 degrees longitude and 60 minutes of Universal Time.
 * Background:**

Interactive: Observing Shadows [] Interactive: Telling Time with Shadows [] Adapted from Shifting Shadows: []
 * References:**