Lunar Cycle Activity

Junior High version, Teachers' guide

What is more familiar than the phases of the Moon? They are recognized by children everywhere, but they are not necessarily simple. There are unsuspected secrets about them waiting to be discovered as you work through this lab.

• Needed materials: bright lamp for sun, moonball (opaque golf balls work better than translucent styrofoam ones), dark room, red flashlight.
• Model every step as instructed using a moonball. Stand up and do it! Don't just sit still and secrete answers by sheer force of thought. The answers are not as important as the method: learn how to use the modelling techniques to come up with reliable answers you can have confidence in.
• Complete each step sequentially, before going on to the next.

I. Model day and night with Mt. Nose

• Your head is the earth; the lamp is the sun; the ball is the moon.
• Mt. Nose is located on the earth's equator.
• Extend your arms out to the side, palms forward. Anything in front of your face or arms is visible "above the horizon." Anything behind you is "invisible" beneath your horizon.
• Mt. Nose turns eastward (to the left) as the earth rotates. Stand up, face the sun, and make the earth rotate one time around, now, in the proper direction.
• Mr. and Mrs. Epidermis live on Mt. Nose.

1. Face the center lamp.
   • Where in the sky do Mr. and Mrs. Epidermis see the sun?
   • What time of day is it?
2. Turn eastward (to the left) until your right ear is toward the sun. Extend your arms so that your right hand is toward the sun, your left hand pointing away.
   • What time of day is it on Mt. Nose?
3. What time of day is it on Mt. Nose when your back is toward the sun?
   • On what part of your head is it daytime?
4. What time is it on Mt. Nose when your left hand and left ear are toward the sun?

1. Look at the picture of the Earth below. The sun is missing! Draw the sun so that it will shine on the day side of the earth.
2. Look at the picture of the Earth below. What is different? The sun is still missing! Draw the sun so that it will shine on the day side of the earth.
3. Look at the sun and earth below. The night is missing from the earth! Color in the night side of the earth.
4. Look at the sun and earth below. What is different? The night is still missing from the earth! Color in the night side of the earth.

II. Model the rotation and revolution of the moon

1. Rotation refers to the turning of a body around its own axis.
   • How long is the rotation of the earth?
   • The length of one rotation of the earth is one "earth day"; the length of one rotation of the moon is one "lunar day," and they are not necessarily the same.
2. Revolution refers to the orbit of one body around another.
   • How long is one revolution of the earth around the sun?
   • The length of one revolution of the earth around the sun is one "year"; the length of one revolution of the moon around the earth is one "month."
3. The diagram below shows the Earth and Moon as viewed from space far above the north pole of the Earth.
   
4. Stand in the noon position with the moon held at arm length in the direction of the sun, as in #1. (The arrows coming from the right represent light rays from the sun.)
5. Identify a mark on your moonball (such as a sporting brand label on a baseball or golfball) and turn the moon so that this mark is facing you. Let the marked side always represent the "near side" of the moon.
   • At position #1, is the marked side (near side) the same as the bright side?
   • At position #1, what proportion of the near side of the moon is illuminated? All, half, more than half, less than half, or none?
6. Move the moon to positions #2 and #3. Keep the marked side toward you at every position.
   • At position #3, is the marked side (near side) the same as the bright side?
   • At position #3, what proportion of the near side of the moon is illuminated? All, half, more than half, less than half, or none?

III. Phase Definitions

What are the different phases of the moon? The bright portion of the moon as seen from the earth changes shape as it passes through different phases. These phases are described by the following terms:


	New Moon: all of the visible side of the moon is dark
	Full Moon: all of the visible side of the moon is bright
	Crescent: the bright part of the moon is a crescent or thumbnail shape
	Quarter: the bright part of the moon is half of the visible side
	Gibbous: the bright part of the moon is lopsided; more than a Quarter but less than a Full

• Note on Quarter phases:
  • A Quarter moon is often called a "half moon," but really only a quarter of the whole moon is both visible and illuminated.
  • The name derives from the fact that when the moon is in a quarter phase, it has passed through either one-fourth or three-fourths of its monthly cycle.

   

• Waxing and waning are used to describe crescent and gibbous moons.
  • Waxing: Just as a candle dipped in wax grows bigger, the bright part of a waxing moon is growing larger from day to day.
  • Waning: When the bright part of the moon is getting smaller each day.

   

• Pass out drawings of each phase to students, or do this activity together, modelling it on an overhead:
  • Identify the name for each phase.
  • Start with the Waxing Crescent phase.
  • "Which phase comes next?"
  • "In what order will the moon pass through its phases?"
  • After students offer their best guess to predict the sequence of phases, observe the Moon for a month to see in what order the phases actually occur.

   

IV. Model Lunar Phases with Mt. Nose

1. Face the sun. Hold your moon directly in front of Mt. Nose as in position 1 of the diagram below. Hold the moon below eye level so it won't block the sun. What is moon's phase?

   

2. Move the moon a little to the left (about 45 degrees) until you observe a thin waxing crescent as in position 2 of the diagram above.
   • Do the horns of the crescent point toward the sun or away from it?
     
3. Move the moon further to the left (about 90 degrees) until it appears half-lit as in position 3.
   • What is the moon's phase? (Don't answer "half" moon.)
     
4. What is the moon's phase at position 4?
   
5. Continue moving the moon around you until the near side (near Mt. Nose) is fully lit as in position 5. You will have to hold the moon above your head.
   • What is the moon's phase?
     
6. Half of the Lunar Cycle, from the New Moon to Full Moon or vice-versa, lasts about two weeks. Continue moving the moon around in a complete circle to represent another two weeks, and identify the phases visible at positions 6, 7, and 8.
   • The complete synodic cycle averages about 29.5 days, or one "moonth" (Old English for "month").
   • In the waning half of the moon's cycle (Waning Gibbous, Third Quarter, and Waning Crescent), is the left or right side of the moon illuminated as seen from earth?
     • By this means can you tell the difference between a Waxing and Waning Crescent, or between a First and Third Quarter?
7. Some time when the moon is visible, hold a ball up in the direction of the real moon outside (do not look at the sun!). Light rays from the sun upon the real moon are parallel to light rays from the sun upon the moonball. Predict: Will the moonball model and the moon show the same phase?

V. Model Eclipses with Mt. Nose

1. Face the sun with your moon between Mt. Nose and the sun. Stand several steps back from the sun, and make sure the moon is much closer to the earth than it is to the sun.
   • What phase is the moon in?
   • Can your lab partner see the moon's shadow on your face? Can you see a shadow on the face of your lab partner?
   • Is the moon's shadow on your face (the earth) as large as your face (the earth itself)?
   • Eclipses are named for the body that is hidden; in a lunar eclipse the moon is obscured, and in a solar eclipse, the sun is covered. Do Mr. and Mrs. Epidermis on Mt. Nose see a solar eclipse or a lunar eclipse?
   • Do the Chin children or the people in Eye City see an eclipse?
   • Why is an eclipse of this type not seen by everyone on the near side of the earth?
   • Why does an eclipse of this sort not happen with every New Moon?
     
2. Turn your back toward the sun and move the moon into the shadow of your head on the far side from the sun.
   • What phase is the moon in?
   • Is this a solar or a lunar eclipse?
   • Can you see the shape of your head when the moon moves into eclipse?
     (When the moon is eclipsed the earth always projects a curved shadow. Does this prove that the earth is spherical?)
   • Is this kind of eclipse visible from the entire night side of the earth?
   • Why does an eclipse of this sort not happen with every Full Moon?
     
3. During solar and lunar eclipses the sun, earth, and moon lie in a straight line, but they are not arranged in the same order.
   • Which body lies in the middle for a solar eclipse?
   • Which body lies in the middle for a lunar eclipse?
     
4. How does the Man in the Moon cut his hair? Answer

VI. Conclusion: Lunar Phases, basic principles

1. Does the moon shine by its own or by reflected light?
2. How much of the Moon is illuminated by the Sun?
3. Are the phases of the moon caused by the earth's shadow blocking light from the sun?
4. Is the far side of the moon the same as its dark side?
5. Does the lighted side of the moon face toward or away from the sun?
6. Does it take a day, a week, a month, or a year for the moon to return to the same phase, e.g., from one New Moon to the next New Moon?

• Click here for a poetic evocation and celebration of moonlight.
• Answer Key for the Lunar Phases lab

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