6-8 > Earth Science
 Grade level: 6-8 Subject: Earth Science Duration: One class period
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Students will understand the following:
 1 A sundial is a tool for estimating time of day during sunlit hours.

For this lesson, you will need:
 • Two-to-three-foot stick • Ten flat rocks approximately 3 to 5 inches in diameter

 1 Ask students if they know what a sundial is. Check students’ definitions or explanations against the following sentence, which is the most basic statement of why we build sundials: During the period of the day when the sun is above the horizon, we can use the constant and steady motion of the sun, and the shadows it casts, to measure the hours of the day by constructing a sundial. 2 On a sunny day, set students the task of making a sundial. They should begin by placing vertically a 2-to-3-foot stick in a protected area of the school yard—an area that receives sunlight all day long. 3 Have your students locate 10 flat rocks, all approximately 3 to 5 inches in diameter. 4 They should paint one of the following times on each rock: 8 a.m., 9 a.m., 10 a.m., 11 a.m., noon, 1 p.m., 2 p.m., 3 p.m., 4 p.m., and 5 p.m. 5 Assign 10 of your students the job of placing a rock at the end of the stick’s shadow for each hour of the school day. 6 Each day for the rest of a week, the students should check whether the rock for each hour is still positioned correctly or whether the rock must be moved somewhat. 7 After the week has elapsed, ask students to explain what transpired regarding the stick, the shadows, and the rocks. Which way did the rocks have to be shifted and why?

 Have students explain and demonstrate how to use a device known as a planisphere. We can use a planisphere as a clock once the sky is dark, on any known date, by observing the positions of the constellations directly overhead. Students can download the parts of a planisphere atotterbeinand follow directions there for putting the pieces together.

 1 Does time exist in the natural world or is time the invention of human beings? In a circular statement, physicists address this question by saying that “we use time to measure motion and we use motion to measure time.” Use this quote as a basis for explaining your understanding of the nature of time. 2 Debate the appropriateness, and the pros and cons, of altering the biological clock of one species with clock DNA from another species. Give examples of what a single organism or an entire species has to gain or lose through such genetic engineering. 3 Many students of the history of the Industrial Revolution suggest that the invention of the steam engine as a portable power resource marked the beginning of worldwide industrialization. Not so, says social critic Lewis Mumford. What do you think Mumford means when he says, “The clock, not the steam engine, is central to the Industrial Revolution. The clock is the crowning achievement that all other machines aspire to.” Is Mumford’s assertion relevant as we enter the communications age? 4 Measuring time is essential for a diversity of human endeavors such as creating music and navigating the surface of the earth. Why isn’t the precision of time measurement as important to the musician as it is to the navigator? What other human endeavors require precision in time measurement and what endeavors require mere approximations in order to be successful? 5 Imagine that you had the ability to travel back in time and could change one event that would significantly alter your life as you now live it. What would that event be, how would you change it, and what would be the consequences to the rest of the world if you were successful? Now imagine the future that you want to live. What events can you control now that will assure you of the future that you want? 6 You now have the ability to precisely locate position anywhere on Earth with the global positioning system (GPS). Suggest five future technologies that will take advantage of this system.

 Assess students in terms of their accuracy in positioning the rocks and their clarity in explaining their findings. Note how students respond to criticism also.

 Design and Construct a Mechanical Clock Using repetitive mechanical events such as the swinging of a pendulum, the persistent drip of water, or the vibration of a weight bouncing on a spring, have students design and construct mechanical clocks that will keep track of the minutes or hours of the day. Each student should use a stopwatch to check the accuracy of his or her invention. When the clocks are complete, students should present them to the class, explaining how the mechanism functions and how accurate it is. History of Time Using the library or the Internet, students can research the history of time and create a time line with the dates of important breakthroughs in our understanding of this phenomenon, including the dates of inventions for measuring and keeping track of time. For example, students may note when Saint Benedict made his contribution to the measurement of time, what the contribution was, and the cultural consequences that grew out of his contribution. Encourage students to use illustrations from their sources to decorate the time line. They might include for the year during which the time line is constructed the cultural events and celebrations that are dependent on astronomical observations—for example, when will or did Passover occur in that year? Tet? Other lunar holidays?

 Biological Clocks: Your Owner’s Manual Sue Binkley. Harwood Academic Publishers, 1997.Learn about human biological rhythms and take the time to read the instructions and complete the chart for measuring your own rhythms. Calendar: Humanity’s Epic Struggle to Determine a True and Accurate Year David Ewing Duncan. Bard/Avon, 1998.Where did calendars come from? Man has tried to measure time and create a usable calendar since the beginning of history. Read this fascinating account of time and calendars.

 Sundials This site includes complete details on the technical aspects of building a sundial with historical references and drawings. The World Clock This site provides up to the minute time in over 100 cities. Julian and Gregorian Calendars An historical reference site on the Gregorian and Julian calendars. A Walk Through Time A “Walk through Time” covers measurement and time from early calendars to the atomic clock of today. Time Service Dept: U.S. Naval Observatory This official time site offers world time zones, moon phases, hours of sunrise and sunset, and lots of time data.

 Click on any of the vocabulary words below to hear them pronounced and used in a sentence. Definition:A precision clock that operates on an electrical oscillator regulated by the natural vibration frequencies of cesium atoms. Context:The constant and high-frequency natural vibrations of the cesium atom provide the world with one of the most accurate time measuring instruments, the atomic clock. Definition:An inherent timing mechanism that is inferred to exist in cells in order to explain various cyclical behaviors and physiological processes. Context:Cellular clocks exist within the cells of plants and animals, helping the organism to survive by reacting and then adapting to the natural cycles of its changing environment. Definition:An instrument designed to mark exact time by a regularly repeated tick. Context:Beginning musicians use a metronome to help them play music with a consistent beat. Definition:The act or result of making events happen, exist, or arise at precisely the same time. Context:As we moved toward industrialization, the success of society and the governance of human behavior required the same kind of synchronization and standardization that made our factories, railroads, and machines work like clockwork. Definition:A slowing of time in accordance with the theory of relativity that occurs in a system in motion relative to an outside observer and that becomes apparent especially as the speed of the system approaches that of light. Context:According to Einstein’s special theory of relativity and as a result of time dilation, time slows down for a space traveler as he approaches the speed of light and the traveler doesn’t age as quickly as does a stationary observer left back here on Earth. Definition:A geographical region within which the same standard time is used. Context:In order to prevent disastrous train wrecks caused by the failure of local communities to agree on a standard measure of time, railroads invented time zones.

 This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.  Grade level:9-12 Subject area:science Standard: Understands motion and the principles that explain it. Benchmarks: Understands general concepts related to the theory of special relativity (e.g., in contrast to other moving things, the speed of light is the same for all observers, no matter how they or the light source happens to be moving; nothing can travel faster than the speed of light). Grade level:9-12 Subject area:geography Standard: Understands the characteristics and uses of maps, globes, and other geographic tools and technologies. Benchmarks: Knows the characteristics and uses of geographic technologies (e.g., geographic information systems [GIS] and satellite-produced imagery). Grade level:6-8 Subject area:technology Standard: Understands the relationships among science, technology, society, and the individual. Benchmarks: Knows ways in which technology has influenced the course of history (e.g., revolutions in agriculture, manufacturing, sanitation, medicine, warfare, transportation, information processing, communication). Grade level:9-12 Subject area:historical understanding Standard: Understands and knows how to analyze chronological relationships and patterns. Benchmarks: Understands alternative systems of recording time (e.g., Egyptian, Indian, Mayan, Muslim, Jewish), astronomical systems on which they are based (e.g., solar, lunar, semilunar), their fixed points for measuring time, and their strengths and weaknesses.

 Ted Latham, physics teacher, Watchung Hills Regional High School, Warren, New Jersey.