Since the dawn of intelligence, man has been trying to make sense of his world. Hunting, gathering, and domestication were spurred by man's desire for understanding, order, and control. Becoming comfortable with the aspects of his world was foremost, knowing the migratory patterns of his prey, the ripening of fruits and grains, and also the ways of the firmament were all crucial steps in early man's development. Before the advent of science, man was attributing the motions of the heavenly bodies to the motions of earthly bodies, seeing the stars in groups resembling bears, lions, or men, naming the friendly face of the Moon after an ancestor or god, or seeing the Milky Way band of stars as the stream of milk given from a heavenly mother to nourish the Earth.

Topic 1: Observing the Moon

The Moon, in particular, has had several names given to it by the many cultures which did and still inhabit the Earth. It was seen by the Greeks as Artemis, the goddess of the hunt, perhaps a reference to the pre-Greek pantheon nocturnal hunting customs. Several cultures have seen the Moon as a god being chased across the sky by a Sun goddess. Some cultures trying to explain the different shapes of the moon (phases) saw them as the story of life and death: the crescent moon is the infant, growing stronger and stronger until maturity at full moon and then growing weaker and weaker and then dying at new moon, only to be born again. The ancient Egyptians called the moon Khonser, which means "traveling through a marsh". Someone traveling through a marsh would be partly obscured by marsh grass for most of his journey, not unlike the appearance of the phases of the moon. Then around 2,000 years ago, the Greeks devised a model to show the moon phases that is still valid now.

What did the Greeks discover which causes the lighted portion of the Moon to appear in several different shapes? The answer is the same reason that the Earth has a day and night. As a sphere, the Moon can have only one half of its shape lit by the Sun at any time. Try to light up more than half of a ball with a flashlight -- it is impossible! Since the Moon goes around the Earth, we have the unique vantage point of being able to at times see the lit and unlit parts at the same time. While trying to light that ball with the flashlight, have a student look at the side of the ball 90° from the lit part, or where the ball appears to only be half lit. The combination of the Moon's period of orbit around the Earth and the direction of the sunlight gives us the monthly change in vantage points, which we call phases, of the Moon.

Activity 6-1: The Phases of the Moon

This activity requires a darkened room and is ideal for small groups. The second part of this activity fulfills same goal but for a larger group

Materials: Strong light; extension cord; two inch Styrofoam ball; pencils.


How long does it take from a new moon to a full moon? To the new moon? What is a lunar cycle? Is it possible to have two full moons ever in one month? If so, how could this be possible?

Activity 6-2: The Moon in Orbit around the Earth

This activity requires a darkened room and can involve a large group

Materials: Large ball (about the size of a basketball); slide projector (or some other bright light source).


Can the students pick out which position was full moon? Quarter moons? Crescents? New moon? Where is the Earth's shadow during the Moon's trip around the Earth? Was the Earth's shadow responsible for the change in shape of the lit Moon? When does the Earth's shadow play a part in the shape of the lit Moon? Which phases of the Moon can be seen in the daytime? In the nighttime?

Activity 6-3: Observing the Moon's Motion

For many cultures, the Moon became an essential tool for survival. Observers of the sky noticed that the Moon's movements were not random and fit a pattern. This pattern would be the foundations of the first calendars (see Chapter 3), and would aide early farmers in predicting planting and harvesting times, or help those living in flood plains of large rivers to be prepared for the rainy season. The moon's regimented pattern can be seen over days and over months in its shape, height in the sky, and location.

Now that the students have seen a simulation of the moon in orbit about the Earth, they should be ready to make actual observations and ask logical questions.

Questions to ask:How does the moon change from day to day? Is it possible to see the moon in the daylight hours? Is there any pattern to the various shapes of the moon? How often does a full moon occur? How could we observe and record the shape and placement of the moon in the sky? When during school hours could we begin this study based on information given in the introduction?

Materials: Sheets of paper 8 1/2" x 11" for each student or small group; heavy cardboard (approximately 9 x 12) for each student or group; pencils; folder such as file folder to store recordings in; Large chart 3' x 6' from standard role; markers; diagram of moon phases; compass.

Morning Observations

Never look directly at the sun.

Begin three days after full moon.

Before beginning this activity, check on the position of the moon and whether it is obstructed. Look for the moon in the western sky.

Activity 6-4: Evening Observations


Discuss observations and the moon's shapes at different times. What patterns have they observed? Can we predict if this pattern will be recurring? What will help us to decide that? What use could we make of this recorded information? How were these observations of the moon helpful in earlier times? Might the phases of the moon contribute to the understanding and ordering of the ancient world?

Topic 2: Origin of the Moon

Although the Moon is one of the brightest objects in the sky, second only to the Sun, it is not an object like the Sun. The fact that the Sun is a body 93 million miles away that can give you a sunburn from its brightness should give a clue as to its very different nature. And although the Sun and the Moon appear the same size on the sky, the moon is actually 400 times smaller in diameter than the Sun.

The Moon is a body similar to the Earth in many ways. The theories of its origin are many and varied: the moon was a piece spun off from the earth, possibly from the Pacific Ocean basin floor, which subsequently caused the continental drift; the Earth had captured a large, perfectly spherical asteroid or meteorite; rings of orbiting materials around the Earth accreted into a moon. The moon is now most widely believed to have formed during a collision between the Earth and a Mars-sized planet in the early period of the Solar System. The pictures below show you a diagram of what theoretically took place.

Part of the objective of the Apollo manned missions to the moon was to take seismographic readings of the Moon, samples of elements from its surface, and measurements of its mass to try and give planetary geologists back on Earth some more data with which to build the best theory of the Moon's formation. The seismographic readouts showed there was little to no motion inside the Moon, meaning there is no activity inside the moon. Activity inside of the Earth tells us that the inside must not be rigid; it must be partially liquid and therefore very hot. It is no wonder that a boiling hot body weighing over 8 trillion gigatons has not cooled down yet! But the smaller moon cooled off quickly.

The elements from the surface combined with the mass calculations and detailed seismographic information about the compositional layers below the surface showed that the Moon is made up almost entirely of crust materials like those on the Earth, mainly silicates, feldspars, and quartzes. The moon has little to no iron core like the Earth does. This data seems to support the collision model which predicts only crust materials from the early Earth and the Mars-like planet would have been flung off from the collision to form the Moon a quarter of a million miles away.

The Moon's diameter is one quarter the diameter of the Earth, around 2000 miles, but its mass is one hundredth the mass of the Earth. This is because of two things, 1) the Moon is made up of lighter materials on the whole, than the Earth, and 2) because mass is a function of the volume of the object, or the length times width times height of the object (one quarter^3).

The insignificance of this amount of mass means that the Moon cannot hold an atmosphere onto its surface tightly enough before the heat of the Sun burns it away. Similarly, water cannot remain on the surface of the Moon long before the Sun evaporates it. The thick atmosphere of the massive Earth acts as a buffer against much of the heat of the Sun, allowing several forms of water to exist on the surface. Earth's atmosphere acts also as a blanket, keeping the heat of the warmed surface inside. Without this blanket, the surface temperatures on the moon are extreme. In the sunlight, temperatures reach 215°F, while in the dark the temperatures plummet to 270°F below zero. The lack of atmosphere on the Moon also permits all forms of space debris to impact the surface, as the cratering bears witness.

The craters are indeed the sites of tremendous explosions on the surface of an object. Craters on the moon range from about 700 mile wide basins to microscopic impacts on dust grains. The majority of craters were formed by asteroids and meteoroids striking the moon's surface. The Earth had just as many craters billions of years ago but our planet developed an atmosphere, creating rain, wind and weather conditions which have wiped out most of the craters. The moon has no atmosphere and no weather so theoretically, craters, rocks, and soil remain the same over billions of years. However, since the majority of impacts occurring on the moon's surface now are from micrometeorites, the "weathering" which occurs is due to the constant pummeling of these tiny impacts. The largest impacts on the moon were around 3.9 billion years ago. The forces of these explosions were strong enough to crack the fragile young moon's crust, allowing the (then) liquid mantle of the moon to seep into the lowlands the crater basins made and cool there into basalt rock. (The dark basalt is similar to the basalt found on the Earth, as we discovered after astronauts visiting these areas brought bits of them back.) These huge, submerged craters are called mare, the Latin word for seas, due to the fact that to the unaided eye, these dark and flat appearing basins look like large bodies of water. Galileo was the first to turn his telescope to the moon and notice that the mare were not smooth, but were cratered like the rest of the surface.

The lightest parts of the moon are called the highlands, as they are above the low basins of the crater fields and are mostly the remains of the material blasted out and upward after the explosions. Rocks collected from the highlands are the oldest rocks on the moon, as they are the remains of the first parts of the moon's crust that cooled 4.5 billion years ago. The whiteness of the rock is due to the fact that the rock is mostly anorthosite, a type of plagioclase feldspar. When broken, the feldspar crystals are ripped from their nice geometric ordering inside of the rock, causing more crystal surfaces to be exposed. The more surfaces, the more places where light can reflect; thus, these broken rocks look very bright.

What about the other side of the moon? It was the Russians who, in 1959, first took pictures of the unseen back of the moon. These historic pictures revealed that this hidden side differs significantly from the side which faces Earth: 98% of the back surface is highlands and there are only a handful of small mare. Additionally, the back side of the moon hosts the largest impact crater known to us in the Solar System. Boasting a diameter of 700 miles, Mare Orientalis is the remnant of an explosion whose force was strong enough to have sent a shock wave around the surface of the moon as far as the other side where it left cracks in the thin crust. The propagation of the shock wave can be seen most prominently in the concentric rings which surround the crater basin itself. The denotation "mare" for this remnant is misleading, as the melted rock in the center of this basin was not the result of a welling-up of liquid mantle from a deep crack in the crust but was rather contact melting of the surface rock from the tremendous heat of the explosion. An unanswered question remains about the moon abut why the crust on the far side seems to be tough enough to withstand an impact which should have destroyed the little moon, while the near side's crust is so thin as to have let mantle material escape.

So, how is the Moon so bright in the sky if it has no bright atmosphere to reflect light and is so very small? The surface of the Moon may be just rock, but those rocks are mostly silicates, sandy rocks. Try breaking up rocks which have lots of white or clear crystals in them. Notice that when broken, those rocks look brighter. This is because more tiny surfaces of the rocks have been exposed each time one piece was broken into many. Since the Moon is constantly being hit by space debris, its rocks are being continually broken up. The surface of the Moon looks bright for this reason. Secondly, 250,000 miles to the Moon is close compared to 93,000,000 miles to the Sun! The Moon may be 400 times smaller across than the Sun, but it is 400 times closer too! So, it appears as big in the sky and very bright.

The moon cannot appear as bright as the Sun, because the Moon is not making its own light like the Sun is. The Moon is instead reflecting the light which has traveled to it from the Sun. Since the intensity of light will decrease over distance, one can imagine that by the time it travels 93 million miles from the Sun to the Moon and then is reflected another 250,000 miles to the Earth, the light is not going to be as intense as if it had just traveled from the Sun to the Earth. So, the Moon will be very bright as the Earth's closest reflective neighbor in space but not as bright as the Earth's closest emitting neighbor, the Sun, is.

Activity 6-5: Relative Dating, Moon Watch

Now that the students have observed the shape of the moon as we see it with the naked eye, they should be ready to take a closer look at the moon. With the knowledge of the origin of our closest neighbor above, students should be able to distinguish between various features of the moon. This activity will allow the students to see another world.

Questions to think about: Is it possible to identify particular craters when observing the moon with an optical aid? Could we find the landing places of the lunar probes?

Materials: Map and model of the moon; telescope or binoculars.


Share pictures and observations. What was it like actually observing the Moon? Was it possible to identify major landmarks? If sketched, was it possible to record all the details? Compare sketches with the map. What time is it for someone living on the middle of the moon during full moon? What time is it on Earth? Can there really be mountains on the moon?

Topic 3: Tides

These activities are most appropriate for students who have had many direct experiences viewing the moon's phases and observing tidal actions.

Anything in the universe which has mass has gravity associated with it. Gravity is difficult to comprehend, save that it is a characteristic of mass, an effect of being massive. It is a force which allows one piece of mass to be aware of any other piece of mass anywhere else in the universe. The awareness comes in the form of a gravitational pull, whereby masses will be attracted to each other and either come together, orbit, or warp each other.

Large bodies of mass already in orbit around another mass will be warped by their proximity to it. The moon, for example, is in orbit around the Earth. Because the Earth is so much more massive than it is, the Earth has warped the moon such that it cannot spin on its axis very fast. The moon's near face is stretched towards the Earth, making it closer to the Earth than it should be. This causes the spin of the moon to slow down such that that face can always point towards the Earth.

This "tidal bulging" can also be seen on the Earth. However, since water is easier to warp than rock, and 75% of the Earth's surface is water, we see the tidal bulging affect in the sloshing of water on the Earth. Thus, the face of the Earth pointing towards the moon at any time will be slightly pulled towards it, or the water will pile up there.

The opposite side of the Earth from the moon also has a tidal bulge. Recall how gravity works: it is dependent upon the masses of the objects and their distance from each other. The side of the Earth farthest from the Moon is dragged less than the center of the Earth, allowing it to be essentially spinning a bit faster. The increase in centripetal force (that outward flinging force like a ball spun around one's head faster and faster) causes the material of the far side, mostly water, to bulge farther out. Thus, two tidal bulges. As the solid Earth rotates past the pull of the moon, different places have different tides at different times.

The Earth tides are also affected by the Sun, obviously, because the Earth is in orbit around the Sun. When the Earth, moon and Sun are in line twice a month at new and full moons, the gravitational pull on the Earth is increased, and tides are higher than at any other times. Conversely, any low tides are at their lowest. These are called spring tides.

When the sun and the moon are at 90 degrees or right angles to the earth (the quarter moons), the gravitational pull of the sun and moon are competing. At these times, the high tides do not rise very high and the low tides do not fall very much. These are called neap tides.

Activity 6-6: Tide Watch

The national newspapers will often have a section nestled somewhere in the weather about the tide times, the sunrise/sunset times, and the phase of the moon. It is to this section in a favorite national paper that this activity will go.

Materials: National newspaper, scissors, glue, paper, pencils.


The height of the tides of the day do depend on the phase of the moon. Why is this? What is the relationship between the heights of the first and second tides of the day? Is it obvious now why there are two tides? If you live in Boston, and the tide is highest at noon during new moon, does this make sense in terms of how the Moon and Earth pull on one another and where Boston is at noon? Drawing and drawing the Earth-Moon-Sun diagrams is very necessary, or else better yet, use a 3-D model with playground balls to understand this relationship.

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