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

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

• 1. Darken room and use extension cord to enable light to be placed in middle of room. Each student places moon ball on the end of a pencil and stands in a circle around light.

• 2. Students imagine that their heads are earth. The ball represents the moon and the light, the sun. They hold their moons at arm's length right in front of the sun.

• 3. Students move the ball a little to the left of the sun looking at the moon until they can see a crescent shape in light. Get them to figure out if this crescent is facing the sun or away.

• 4. Students keep moving their moons around their heads (earth). They stop when half the moon is in light. As the moon grows fuller is it moving towards or away from the sun?

• 5. They move the moon in a circle until they can see it fully lighted. To accomplish this, they must hold the moon above their heads. When they observe the ball fully in light ask if it is between them (earth) and the sun or on the opposite side of them and the sun?

• 6. Students continue to move the moons until they are half full again. As it move toward the sun is it getting fuller or thinner.

• 7. Have them move their moons so that they become crescent slivers. Then explain that when the moon passes the sun it usually is just above or below it and we cannot see it. Why not? this is the phase we call the new moon. It is called new because the ancients thought it was newly born each time.

• 8. Repeat this activity several times making sure that the light source is appropriate so that the phases can be clearly seen.

Discussion

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

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

• 1. Set up the students in a circle so that they are all facing outward, and have them sit. The students are representing different observers around the surface of the Earth.

• 2. Set up the slide projector so that the main beam of light passes over the circle without shadows from the students. The slide projector is the Sun.

• 3. Have one student carry the ball over his head and walk counterclockwise outside the ring of students, so that the same half of the ball is always being hit by the light. He is demonstrating the Moon in orbit around the Earth. Have this student stop periodically to allow students in the circle to observe what the ball looks like. Perhaps on paper they should draw the ball and the part of it which is lit each time he stops.

Discussion:

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.

• 1. Students should practice measuring techniques in classroom. Stand with arms raised above heads. Hold one hand blocking an imaginary sun to protect eyes. Form a fist with other hand and point the wide part to the sun. Move the fist toward the moon counting each fist placed. Practice several times.

• 2. Measure and draw the moon's shape and position in relation to the Sun. Find a place to stand facing South. On the recording sheet, students should place an S in the middle of the top of the paper, E on the left hand upper corner, W on the right hand corner and than draw the horizon leaving a large space for the sky.

• 3. Observe and record daytime moon and sun every other day (does not need to be at the same time) labeling each drawing with the date of the observation and the distance between the moon and sun measured in fists.

• 4. Discuss the changes in shape and distance from sun after observations. After each observation, ask students if the curved part of the moon is facing toward or away from the sun. Ask them to predict where the moon will be after a few days and also to predict how far from the sun it will be in fists.

• 5. After about five measurements, the observations may be summarized on a large sheet of paper. The moon is no longer visible during the morning ten days after the full moon. Place a large chart on the wall. Draw or have students draw horizon objects and label directions. Start with the first observer. Ask the students to use their observation sheets to describe the shape of the moon on that day. Have them share their fist measurements and use the average of these. Draw the sun and moon as they looked on the day of observation. Write this date and the number of first measurements under moon. Record all other observations in fists and shapes.

Activity 6-4: Evening Observations

• 1. Students should think about and discuss why the moon is no longer visible during the day. They should think about and predict when and where it will be visible again.

• 2. Two or three days after the new moon, students watch at sunset to see when the moon first appears near the setting sun. It will appear as a thin crescent. They record the setting sun and then draw the moon every other clear day at sunset with the date and fist measurement from setting sun to moon and the fist measurement from horizon. They do this on clear days until the full moon which is about two weeks after the new moon and add their recordings to their folders.

• 3. Place another large sheet of paper on wall and draw observations as in daytime observations showing number of fists away from moon to sun, number of fists from horizon to moon, and the date of observation.

Discussion:

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?

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.

• 1. Students observe the moon through a telescope or binoculars carefully to observe and become familiar with its topography.

• 2. Students may examine the map of the moon and moon globe and use the key to identify some craters, mare, and the lunar probe landings (numbers with asterisks). How did the features get their names? What names might they choose for these lunar landmarks? Where might the name Apollo have come from? What might they name a lunar space ship?

• 3. The students might view the moon again. How could they watch a sunrise on the moon such as Galileo did with his first telescope? Are they able to find the mare and craters after studying the map and globe? Watch the moon again and observe the pattern on the landscape. Can students predict if the topography will change? Can the layering of craters on craters and the placement of the mare give studetns an idea of the chronological history of the moon's bombardment and volcanic era?

• 4. Optional: Sketch the moon during observation.

Discussion:

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?

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.

• 1. Students (or the class) should collect a month's worth of the tidal report sections of the newspaper and glue each day's report to the upper left of a single sheet of paper.

• 2. For everyday of that month, observe which phase of the Moon was happening. If you can't do this, often the tidal report will tell you, or you can look it up in an almanac or online.

• 3. On the rest of the paper, students should be able to draw the corresponding phase of the moon with respect to the Earth, referring to the drawing in the previous activities with how to draw different phases. In other words, if the phase of the moon is first quarter, then the drawing would have the moon drawn directly to the left of the Earth with the Sun directly above the Earth. For each day, this kind of diagram should be drawn according to whatever phase the report describes for that date.

• 3. Comparing the heights of the tides and the phase of the moon, can a correlation be found? When is noon in the diagram? 6 P.M.? Can a graph be made of height versus phase?

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.