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Telling Time By The Light Of The MoonTelling-Time-By-The-Light-Of-The-Moon

  • Subject: Space Science
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  • Grade(s): 6-8
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  • Duration: Two class periods

Lesson Plan Sections


Students will:
1. understand that local solar time is determined by the position of the sun relative to an observer's horizon
2. identify by name the phases of the moon—waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent, and new
3. define elongation as the measurement of angular distance (in degrees) between a line of sight from an observer on Earth to the sun and a line of sight to any other celestial object
4. understand that the phase of the moon depends upon the measurement of the eastern or western elongation of the moon from the sun.


For this lesson, you will need:
transparency film for ink-jet or laser printer (optional)
-Worksheet I: Lunar Phase Flip Book
-Worksheet II: Lunar Phases and Elongation from the Sun
-Template A: Telling Time with Phases of the Moon
-Template B: Telling Time with Phases of the Moon
-Template C: Telling Time with Phases of the Moon
-Activity: What Is the Diameter of the Moon?


1. Introduction:
Share this quotation with your students: "And God said: Let there be lights made in the firmament of heaven, to divide the day and the night, and let them be for signs, and for seasons, and for days and years." (Genesis 1: 14)
Explain that every culture on this planet has looked toward the heavens to help organize events on Earth. Without a precise calendar based on the annual motion of the sun through the stars, we would not know when to plant and when to harvest, and civilization's chance of survival would be at risk. The annual calendar is further divided into months, recognizing the 29.5-day period of the moon's phases. And finally, the days of our lives are marked by the daily rising and setting of the sun.
As we learned to navigate this sphere we call Earth, it became necessary to divide the day into 24 hours so that ships at sea could determine the relative local solar time and longitude from that of their home port. Sundials are primitive clocks that help us to determine the approximate hours of the day while the sun is above the horizon. How can we count on nature to help us determine the approximate hour during the nighttime? We use the light of the moon!
Tell your students that in this activity they will be learning the phases of the moon. They will also learn how they can use the moon's position relative to the horizon and to the sun to determine the approximate hour of the night.
2. Students will become familiar with the cycle of lunar phases by creating a "flip book" of photographs showing various stages of the lunar phases.
  1. Print out the 26 lunar phases onWorksheet I: "Lunar Phase Flip Book."
  2. Cut out each picture and paste it to the edge of an index card.
  3. Arrange the 26 cards in order and staple them together at the top of the cards.
  4. As the students flip and view the animation, have them make a distinction between that part of the phase cycle characterized as "waxing" and that part characterized as "waning." Using the cards, have the students identify the phases as new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, and waning crescent.
3. The phase of the moon is dependent on the angular distance between it and the sun (which illuminates the moon). Depending on whether the moon is to the east or the west of the sun, this angular distance is called the eastern elongation or western elongation . For example, when the moon is in the first quarter phase, it is at 90 degrees eastern elongation from the sun. Use a standard earth science or astronomy text to review the causes for lunar phases with your students, and then tryWorksheet II: "Lunar Phases and Elongation from the Sun." Print out one copy for each student.
4. By observing and naming the current phase of the moon, the elongation from the sun can be estimated. This elongation estimate will help to locate the position of the sun somewhere below the horizon. Since it is the position of the sun that determines the local time in hours, we can estimate the hour of the night without actually "seeing" the sun.
  1. Print outTemplate A: Telling Time with Phases of the Moon.
  2. Print outTemplate B: Telling Time with Phases of the Moon.
  3. Follow the instructions on each template and assemble them. Place a thumbtack through the center dots so that Template B can rotate on top of Template A.
  4. Use the completed construction to review the meaning of local solar time . Local solar time is determined by the position of the sun. Wherever the sun is located, above or below the horizon, determines the approximate local solar time.
5. Once students become comfortable with determining the local solar time with the device constructed in part 3, print outTemplate C: Telling Time with Phases of the Moon and add it to the previous assembly. The final assembly should look like this:

Note: All three templates may be printed onto pieces of overhead transparency film that are suitable for use with an ink-jet or laser printer. If this is possible, the teacher may find it more convenient to instruct students on how to use the device to determine the local solar time with the aid of an overhead projector.
6. This device can also be used for determining the hour of the night by observing and naming the current lunar phase:
  1. On a clear night, look for the moon and identify its phase.
  2. Find the identified phase on your template circle using the lunar phase images.
  3. Turn the lunar phase template until the correct lunar phase image is roughly over the horizon template in the same way as it appears over the real horizon.
  4. Determine the elongation from the sun for this phase, and rotate the sun template carefully (without rotating the moon phase template) until it is at the determined elongation.
  5. Read the hour of the night from the clock printed on the horizon template.
Example: Imagine that you are viewing a waxing gibbous moon located directly above the southern point on your horizon. Place the image of the waxing gibbous moon on the lunar phase template directly over the southern point on the horizon template. When the moon is waxing gibbous, it has a 135-degree eastern elongation from the sun. Taking care not to move the moon image template, rotate the sun template approximately 135 degrees away from the image of the waxing gibbous moon so that the moon will be properly placed at 135 degrees east of the sun. Read the hour of the night shown next to the sun. If you have carefully followed these instructions, the time should read 9: 00 p.m.

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Adaptation for older students:
Throughout history, geometry has played an important role in helping us determine the size, shape, and placement of all the objects in our solar system—particularly our moon. Older students can challenge their creativity with the activityWhat Is the Diameter of the Moon?In this activity, they will use geometry to measure and calculate the diameter of the moon during its full phase.

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Discussion Questions

1. Compare the relative motion of the moon and the sun as they "chase" each other through the constellation of stars on a day-to-day basis. Describe how you might determine their individual rates of motion through the stars in degrees per day.
2. Ocean tides are caused by the combined gravitational interactions between the Earth and the moon and between the Earth and the sun. Explain why the difference between high and low tides is more extreme when the moon is in either the new phase or the full phase.
3. There are many references to the various phases of the moon in art, music, literature, religion, and other cultural experiences. Debate which cultural events, celebrations, and icons would not exist if the Earth did not have its companion moon to inspire human creativity.
4. Lunar eclipses can be observed about twice a year by everyone on Earth when the moon is in a full phase. Explain why a lunar eclipse does not occur for every full moon during the year.
5. Theorize why solar eclipses, which happen only when the moon is in its new phase, occur even less frequently then lunar eclipses. When they do occur, why do so few people on Earth see them?
6. The lunar cycle of phases takes 29.5 days (the synodic period), but it takes only 27.3 days (the sidereal period) for the moon to make a complete 360-degree orbit of Earth. Explain why there is a discrepancy between these two periods.

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Position a student in the front of the classroom with a basketball representing the moon held outward at arm's length. As the student, who represents Earth, and the "moon" turn slowly in a circle, illuminate them from the back of the classroom with a bright light source (such as an overhead projector) representing the sun. Randomly call out the names of various moon phases and ask the student to stop turning when the "moon" demonstrates that phase from the student's point of view. Have the other students critique the correctness and accuracy of each phase demonstration.
To assess student understanding of the measurement of lunar elongation and its relationship to the phase of the moon, ask the student demonstrator to stop at various elongations, such as 90 degrees west elongation and 135 degrees east elongation. Students should critique this demonstration and predict which phase will be observed from the demonstrator's point of view. Have the demonstrator confirm or correct the class's phase predictions.

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What If There Were No Moon?
Explain to students that we believe the moon and its cycles affect the life cycles of creatures great and small here on Earth. There is even some suggestion that if we had never had a moon, life would not have evolved at all on Earth. Have students use references from the library or the Internet to find 10 concrete examples of how the moon affects life in the simplest to the most complex species on the land, in the air, and under the sea.

Why Do We Have a Moon?
Point out to students that not every planet in our solar system has a moon. Some have two moons, and some have many. Moons come in a variety of sizes, shapes, and compositions, suggesting that there may be several different origins of the moons in our solar system. Three theories are in competition with one other regarding the origin of the Earth's moon. The theories are known as the "molten proto-Earth theory," the "capture theory," and the "planetary impact theory." Currently scientists supporting the planetary impact theory seem to be winning the debate. Have students research and report on each of the three theories and explain why the planetary impact theory seems to be preferred at this time.

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Suggested Readings

The Planetary Report
A Publication of the Planetary Society, (magazine) J/F 1999
Excellent information on the moon, and other moons in the solar system great pictures and text.

Sky and Telescope
9/99, 118-123, 5/99, 36-38, 3/99, 53-55.
These three publications of Sky and Telescope explain "Lunar glows, clouds and volcanoes" and the hype behind a blue moon.

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National Air and Space Museum
Information about a variety of flight and space related topics.

Jet Propulsion Laboratory's Home Page
Space information.

Space Shuttle Home Page
Information about space shuttle flights.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    elongation
Definition: The angular distance of a planet or other celestial body from the sun.
Context: When the moon is full, it is a full 180-degree elongation away from the sun.

speaker    local solar time
Definition: The time of day reckoned by the sun, based on 12 o'clock noon occurring at the instant of the transit of the sun's center over the meridian.
Context: When the two cowboys met face to face on Main Street, the local solar time was "high noon," and I could see that the sun was as high as it would get in the sky on that fateful day in Tombstone.

speaker    lunar phase
Definition: One of the cyclically recurring apparent forms of the moon.
Context: I noticed that with each passing night the lunar phase changed from a mere sliver of light in the sky that chased the setting sun over the western horizon into a bigger and rounder full moon that shone down upon me all night long.

speaker    waning moon
Definition: The moon during the phases in which it exhibits a decreasing illuminated area.
Context: I don't like to go out after dark during a waning moon because night after night it gets darker and I get scared.

speaker    waxing moon
Definition: The moon during the phases in which it exhibits an increasing illuminated area.
Context: As the waxing moon grew brighter each night, I found it easier and safer to find my way along the path through the park on my way home from work.

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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: Grades 6-8
Subject area: Science
Understands essential ideas about the composition and structure of the universe and the Earth's place in it.
Knows how the regular and predictable motions of the sun and moon explain phenomena on Earth (e.g., the day, the year, phases of the moon, eclipses, tides, and shadows).

Grade level: Grades 6-8
Subject area: Mathematics
Understands and applies basic and advanced properties of the concepts of measurement.
Understands the basic concept of rate as a measure (e.g., miles per gallon).

Grade level: Grades 6-8
Subject area: Mathematics
Understands and applies basic and advanced properties of the concepts of geometry.
Uses geometric methods (e.g., an unmarked straightedge and a compass using an algorithm) to complete basic geometric constructions (e.g., perpendicular bisection of a line segment and angle bisection).

Grade level: Grades 6-8
Subject area: Thinking and reasoning
Understands and applies basic principles of logic and reasoning.
Understands that some people invent a general rule to explain how something works by summarizing observations.

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Ted Latham, physics and science/technology teacher, Watchung Hills Regional High School, Warren, New Jersey.

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