Spring 2001

Moon workshop  Astronomy & Cosmologies

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GOALS: (A) To develop an understanding of why the moon exhibits different phases. (B) To develop an understanding of what causes lunar eclipses. (C) To develop an understanding of what causes solar eclipses. (D) To extend lunar phase understanding to planets and put constraints on models of the solar system. Assumptions: The Earth, Moon, and Sun are approximately spherical. The Moon orbits the Earth. ACTIVITIES: Thinking and drawing: A. Phases of the Moon B. Eclipses of the Moon Experimenting: A. Phases of the Moon B. Eclipses of the Moon Extra: C. Solar eclipses D. Planetary motions Do these activities in a group of two or three.  Discuss your ideas and observations with classmates.

(A) What causes the phases of the moon?
The questions in this section are designed to elicit trial ideas from you.  Use your imagination, not your textbook!
Later, thinking through distinctions between new moon and lunar eclipse will lead you to develop consistent explanations of both.

How much of the Moon receives sunlight at a given time? Always half the Moon? Sometimes more or less than half? Why?
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During new moon (when the moon appears dark, unilluminated) is sunlight falling anywhere on the Moon's surface? If not, why not? If so, why don't we see it?
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At new moon, is the Earth or the Moon closer to the Sun?
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Which is closer to the Sun at full moon?
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Draw diagrams of the relative positions of Earth, Moon, and Sun at New Moon and Full Moon.

New Moon	Full Moon
. . . . .	. . . . .

Try to agree on one sentence summing up the relative positions which can result in a new moon.
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(B) What causes eclipses of the moon?
The questions in this section are designed to elicit trial ideas from you.  Use your imagination, not your textbook!

When we see the moon go completely dark in a lunar eclipse, is sunlight falling anywhere on the moon's surface? If not, why not? If so, why don't we see it?
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What are the relative positions of the earth, moon, and sun in a lunar eclipse? Draw a diagram. Are there other possible orientations?
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Try to agree on one sentence summing up the relative positions which can result in a lunar eclipse.
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Compare the relative positions of the earth, moon, and sun in these two cases.

New Moon	Lunar Eclipse
. . . . .	. . . . .

Try to develop one sentence summing up the differences in the orientations which cause lunar eclipses versus new moons.
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(A) Get a styrofoam moon-on-a-stick. Let your head be the earth, and let your eyes be at your position on the earth. In a dim room, let a light bulb at about head level serve as the sun. (Overhead or fluorescent lights won't do: you need something closer to a point source.) Standing in one place, revolve the styrofoam moon around your earth-head at arm's length.

Where do you observe a half-moon, quarter moon, etc.? Draw a diagram. You may need to adjust the plane of the moon's orbit.
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(B) How can you make a lunar eclipse with your styrofoam moon?
Draw a diagram. You may need to adjust the plane of the moon's orbit.
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What's the difference between a lunar eclipse and new moon, based on your observations?
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(C) How can you make a solar eclipse (when the moon makes the sun go dark)? You may need to adjust your distance to the lamp-sun. Draw a diagram.
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Try to agree on one sentence summing up the relative positions which can result in a solar eclipse.
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The planet Venus exhibits phases much like those of the moon. What does this tell you about the possible relative positions of Venus, Earth, and Sun?
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From Earth, we never observe phases of the planet Mars. What does this tell you about the possible relative positions of Mars, Earth, and Sun?
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Under what conditions could an observer on Mars see phases of Earth? Where could you stand to see phases of Mars?
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Develop two different models of the solar system which are consistent with the Moon's phases Venus' phases and Mars' absence of phases. Draw diagrams.
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