The Moon Phase Book
Produced by Billy Hix and Terry Sue Fanning As part of the TeachSpace Program
For more ideas and an image of the current phase of the moon, visit:
www.teachspace.us
Printing Date: 10/29/2010
Brief Explanation of the Moon Phases
The phases of the moon are caused by the relative positions of the earth, sun, and moon.
The sun always illuminates the half of the moon facing the sun (except during lunar eclipses, when the moon passes thru the earth's shadow). When the sun and moon are on opposite sides of the earth, the moon appears "full" to us, a bright, round disk. When the moon is between the earth and the sun, it appears dark, a "new" moon. In between, the moon's illuminated surface appears to grow (wax) to full, then decreases (wanes) to the next new moon.
The edge of the shadow (the terminator) is always curved, being an oblique view of a circle, giving the moon its familiar crescent shape. Because the "horns" of the moon at the ends of the crescent are always facing away from the setting or rising sun, they always point upward in the sky. It is fun to watch for paintings and pictures which show an "impossible moon" with the horns pointed downwards.
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Phases of the Moon
The Moon appears to go through phases. In other words, the amount of the Moon that we can see changes over time in a cyclic period that repeats itself approximately once a month. The cause of these phases is the relative positions of the Sun, Earth, and Moon.
As seen in the diagram, if the Sun is located off to the right of the picture, the Earth and Moon are illuminated as shown (the white areas being the lighted areas). Notice that no matter what phase the Moon is in, HALF of it is ALWAYS lit by the Sun. (Which half is always lit? The half that is facing the Sun.) The reason that we do not always see a Moon which is half lit is because of our position relative to the Moon and the Sun. As the Moon moves in its orbit, different portions of it appear (to us!) to be lit up as we look at it from Earth. This is why we see lunar phases.
For example, if the Moon is at position 1 in the diagram, the half of it that is lit by the sun is facing away from us, so we do not see the moon at all. This is called a new Moon.
When the Moon is at position 3, we see half of the half of the Moon that is lit up. We call this a quarter Moon. The important point is that the moon doesn't change, nor does the amount of the Moon which is lit by the Sun. The only thing that changes is the position of the Moon relative to us and the Sun. This change in position causes the phases.
Waxing vs. Waning
The diagram above shows what the different phases of the Moon would look like as seen from Earth (note that the numbers below each phase correspond to the different positions of the Moon as seen in the first diagram). It appears that the Moon repeats certain phases:
there are two crescent, gibbous, and half phases each month (each cycle). These phases are not exactly identical, however. Look closely at the diagram. You will notice that during phases 1 through 5, the amount of lighted area increases over time from right to left. When this occurs, the Moon is said to be waxing. During phases 5 through 8, the amount of light area decreases (or the darkened area increases) from right to left. When this occurs, the Moon is said to be waning. Therefore you can tell if the Moon is waxing or waning based on whether the right side of the Moon is dark or light. (Of course, this only works in the Northern Hemisphere. In the Southern Hemisphere the effect is just the opposite!) Astronomers use this to distinguish between the repeated phases of the moon by referring to the waxing or waning crescent, gibbous, and half phases.
Telling Time
The phase of the Moon can tell you the time of day. For example, because a full Moon is seen when the Moon is on the opposite side of the Earth from the Sun, an observer on the Earth will see the Moon rise just as the Sun sets. The next day, the Moon will rise
approximately one hour later (because the Moon will have moved farther along on its orbit). This means that a waning half Moon will rise at midnight, a new moon at dawn, etc...
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Moon Phase Questions
1. Would a Frisbee fly on the moon? What about an airplane? When the Apollo missions landed on the moon, why did they not use a
parachute?
2. How many men and how many women have walked on the moon?
3. If you see the moon in the east at 3:30pm, is the moon waxing or waning?
4. If the Moon is only showing one face to earth, is it due to the fact that it is not rotating?
5. The moon obits the earth in an elliptical orbit, is that why it looks closer when the full moon is close to the horizon?
6. How many tides in one location on the earth does the moon generate in one 24 hour period?
7. Do all of the planets orbit the sun in the same direction?
8. How long did it take for Apollo astronauts to travel to the moon?
9. When the moon is in the first quarter, the moon will rise about what time of day?
10. If you see the moon in the west at 8am, is the moon waxing or
waning?
Why are there both high and low tides?
The question is what makes low and high tides?
As I'm sure you understand, the tides are caused by the gravitational attraction of the Moon. Most people have no problems understanding why, when the Moon is directly over head there are high tides - but then they ask why there are two tides a day! It is also a good question to ask why there are low tides.
The presence of the Moon deforms the shape of the Earth slightly, and since the water is the oceans moves much more easily than the land, we mostly see this deformation in the form of tides in the ocean (but the land does move slightly too). The force of gravity varies inversely with the distance from the object (i.e. it gets weaker the further away you are), so the part of the Earth closest to the Moon is pulled towards it slightly more than the centre, while the part furthest away is pulled towards it slightly less. This means that the Earth becomes (very slightly) egg shaped, and since there is only so much water to go around this causes high tides on the "front and back" of the Earth (as seen from the Moon) and low tides on the sides.
Below is a nice diagram illustrating this.
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Conduct the Moon Phase Experiment in your Classroom
Items Needed:
• Work light
• Ping Pong balls
• 1/8 inch wooden dowels
• Print out of baseball bases
To remember the phases of the moon, students need to be able to relate the phases of the moon and the positions of the earth, sun, and moon to something they can relate to. We will use a baseball diamond.
You need to print out some paper “bases” for home plate, first, second, third base, and the pitcher mound.
Start by placing your work light at about eye level in the position that the umpire would stand. Place your printouts of the 4 bases on the floor in your classroom, about 10 feet between each base (this number is not important and is determined by the strength of your light beam in your work light). Place home base in front of your work light and work your way around the bases. Place your pitchers mound in the center of the 4 bases.
Have a student stand on the pitcher mound and hold his moon toward home base. This is a new moon.
As the student moves his hand towards first base, he should see the phase of the moon change on his moon stick. When he is pointing to first base, he is at the phase first quarter.
Now rotate toward 2nd base. This is a full moon.
Now continue toward 3rd base. This is the last quarter.
As the student continues toward home plate again, make sure that they are looking at the changing moon phase on the moon stick. Once back at home plate, they are back to a new moon.
Telling time with the Moon
It is important for students to relate the time of night or day to the phase of the moon.
The times given are approximations. No consideration was given to daylight savings time or the changing of the rising and setting of the moon due to changes in of the seasons. It was made simple to make it easier to remember.
Telling time:
New Moon: The new moon will rise and set with the sun. We will use the time of 6am for the raising of the new moon.
First Quarter: The first quarter will rise at noon and will sit at midnight.
Full Moon: The full moon will rise at sunset and sit at sun rise. We will use the time of 6pm for moon rise.
Last Quarter: The last quarter will rise about midnight and sit at noon.
To reinforce:
Visit the web site www.teachspace.us and look on the home page. You will see a current moon phase display. Make this your homepage for one month and follow the phase of the moon each day. Make it part of your morning routine. Challenge the students to look at the “real” moon to see if it matches the phase displayed on the web site.
