The Moon
Phases of the Moon
Return to the laboratory website (www.ric.edu/psci103/Earth&Moon)
Select Exploring Earth Visualization
In this simulation there is a composite view of the phases of the moon as seen from earth, and a view
as seen from the perspective high above the earth-moon system. You will use both of these during
the simulation.
The simulation starts with the position of the earth and moon during the Full Moon phase. There
are two buttons to start and stop the animation. Click  to begin the animation. Watch the
changing phases of the moon while the moon orbits the earth.
Stop the animation at a New Moon by clicking the
button.
From which direction of the screen is the sun located?
How much of the surface of the moon is illuminated by the sun?
How much of the surface of the earth is illuminated by the sun?
How much of the illuminated surface of the moon is visible from earth?
Start the animation and stop the lunar cycle at a First Quarter Moon.
How much of the surface of the moon is illuminated by the sun?
As viewed from earth, what side of the moon (right or left) is the moon illuminated?
As viewed from earth, how much of the illuminated moon’s surface is observed?
Start the animation again and stop the lunar cycle at a Full Moon.
How much of the surface of the moon is illuminated by the sun?
As viewed from earth, how much of the illuminated moon’s surface is observed?
Start the animation again and stop the lunar cycle at a Third Quarter Moon.
As viewed from earth, what side of the moon (right or left) is the moon illuminated?
As viewed from earth, how much of the illuminated moon’s surface is observed?
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More Details of the Lunar Cycle
Return to the laboratory website (www.ric.edu/psci103/Earth&Moon)
Select Lunar Cycle Simulation
This simulation is very similar to the previous one, except that it provides a bit more information
regarding the phases of the moon. In the previous simulation you stopped the motion of the moon
in its orbit around the earth every one quarter of an orbit (90 o). In this simulation you will stop the
simulation every 45o to determine the percent illumination, the names for each of the phases, and
the angle formed by the sun-earth-moon for each phase.
The controls for navigating this site are very straightforward. Start and stop the animation and
complete the diagram below, listing the names of the phases and drawing the appearance of the
moon and its direction (clockwise or counter-clockwise) as it orbits the earth.
Sun
Earth
The reason why we only see a portion of the half-illuminated moon is due to the sun-earth-moon
angle. While half of the earth is illuminated and half of the moon is illuminated at all times,
because of the position of the moon and earth we are only able to see varying amounts of the
illuminated side of the moon.
Notice that each of the names for the phases of the lunar cycle are in increments of 45 o . Starting
with a New Moon, notice that the sun, moon, and earth are in alignment, with the moon in
between the earth and sun. This is an angle of 0o.
Since the moon orbits the earth in a counter-clockwise direction, the angle formed between the
sun and moon as observed from earth increases, with the moon on the left-side of the sun. Since
the moon is to the left of the sun, this means two things:
1. The right side of the moon (as observed from earth) is illuminated.
2. The moon is following the sun in the sky as they both make their way from the eastern
horizon (where they rise) to the western horizon (where they set).
Complete the table at the end of the laboratory collecting the information from the simulation.
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MODELING THE MOTION OF THE MOON
Use the globe, the yellow sphere as the sun, and the ping pong ball as the moon to illustrate the
orientation of the sun-earth-moon system. Place the sun on the laboratory table and orient the
moon between the earth and sun to represent a new moon. Place the side of the ping pong ball
with the insignia towards the earth so to show that this side of the moon remains facing earth.
Move the moon counter-clockwise around the earth approximately 45o while keeping the insignia
pointed toward the earth. What lunar phase is represented? Did you rotate the moon to achieve
this phase?
Move the moon counter-clockwise again so that the sun-earth-moon angle is 90o, again while
keeping the insignia pointed toward the earth. What lunar phase is represented? Did you rotate
the moon to achieve this phase?
Continue moving the moon through the entire lunar cycle, noting the sun-earth-moon angle. You
should see that the same side of the ping pong ball always faces the earth, that is the moon
rotates with the same rotational period as its orbital period. The moon is said to have a
synchronous rotational period so that the same side of the moon is always oriented toward the
earth. (Go to the link from ExploreLearning to observe the moon’s synchronous orbit in action.)
Diagram of
Phase
Phase Name
Sun-EarthMoon Angle
%
Illuminated
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ANALYSIS
1. What is meant by the term “waxing”? What is meant by the term “waning”?
2. When the moon is waning, is it located to the right or to the left of the sun in the sky?
3. Which will set first, the sun or the moon when the moon is waxing? Which will rise first when
waxing?
4. Which will set first, the sun or the moon when the moon is waning? Which will rise first when
waning?
5. The angle formed by the full moon and the sun is 180o . If I see the sun setting in the west,
where will I find the rising moon? Explain your reasoning.
6. The angle formed by the first quarter moon and the sun is 90o. If the sun is setting, would I be
able to see the moon? Where in the sky would I look to see the moon?
7. What phases of the moon can be observed only during the day (while the sun is above the
horizon)?
8. What phases of the moon can be observed only during the evening (while the sun is below the
horizon)?
9. We see only one side of the moon. Does the moon rotate on its axis? If it takes 29 days for
the moon to complete one lunar cycle, how long does it take the moon to rotate one about its
axis?
10. Google “solar eclipse”. What is the orientation of the sun-earth-moon for a solar eclipse to
occur? What phase must the moon be in to have a solar eclipse?
11. Google “lunar eclipse”. What is the orientation of the sun-earth-moon for a lunar eclipse to
occur? What phase must the moon be in to have a lunar eclipse?
12. Why are solar and lunar eclipses so rare?
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Lunar Features
Because the moon spans 3476 kilometers, about a quarter the diameter of Earth, and lies only a
quarter million miles away, it exhibits a wealth of detail in a small telescopes and binoculars. Both will
reveal the Moon's desolate landscape punctuated by bright highlands, dark plains, and rayed craters.
At every phase except when full, you'll notice that the lunar globe is divided by the terminator, the
line separating the Moon's bright, sunlit side from the side hidden in shadow. Here is where surface
features stand out best. Seen in a small telescope or high-power binoculars, the landscape near the
terminator stands out in bold contrast and detail. The terrain looks very rough near the terminator
because here the Sun is near the lunar horizon. Thus every low hill casts a long, black shadow that
creates an exaggerated impression of height.
The term 'meteorite impact' is used to describe the process of surface bombardment by cosmic
objects. The objects themselves are variously referred to as impactors or 'projectiles'. The impact
process is explosive, impacting the surface at more than 20 km/sec (45,000 mi/hour). Upon impact,
the impactor vaporizes and the planetary or lunar material is compressed and is tossed out of the
target area, piling up around the hole with the bottom of the crater lower than the original ground
surface with the piled up material on the rim higher.
PART I: SIZE OF LUNAR FEATURES
To determine the size of any lunar feature you must first determine the scale of the photograph.
Using a ruler, measure the diameter of the Moon (Image #1) to the nearest millimeter. The moon’s
actual diameter is known to be 3476 km. Determine the scale of your photograph in km/mm.
Diameter of lunar image = __________ mm
Scale of Image #1 = __________ km/mm
To determine the magnification of Image #2 measure the distance from the centers of the craters
Plato and Cassini on Image #1 and Image #2. From these measurements determine the magnification
of Image #2.
Distance Image #1 = __________ mm
Distance Image #2 = __________ mm
Magnification = ________ __ times
The surface features on the full image are blurry making accurate measurements difficult. By knowing
the scale of the lunar image and the magnification of the inset (Image #2), you can now calculate the
diameters of the two craters, Plato and Cassini with greater accuracy as they appear in Image #1.
Compare your results with the known diameters of the two craters (Google it!)
Crater
Measured Diameter
Image #2 (mm)
Calculated Diameter
Image #1 (mm)
Calculated
Diameter (km)
Actual
Diameter (km)
Plato
Cassini
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Height of Lunar Features
The height of a certain lunar feature such as mountains or craters can be calculated by analyzing the
length of their shadows. In the figure below you are viewing the moon from above one of its poles.
S
M
sunlight
T
B
C
In this diagram MB represents the height of a
surface feature, such as a mountain, BC is the
moon’s radius, MS is the length of the shadow as
seen from Earth, and BT is the distance of the
mountain from the terminator. Notice that each of
the two triangles are right triangles so that the
ratios of the sides are equal. So that:
MB
BT
=
MS
(Equation 1)
BC
Since we are interested in the height of the surface feature, rearranging results in:
(MS) (BT)
MB =
(Equation 2)
BC
Remembering your algebra, we must know all of the terms on the right hand side of the equation to
determine the height of the crater. BC is the Moon’s radius, which is known (from Part I) and BT, the
distance of the mountain from the terminator can be measured from the full lunar photograph
(Image #1). The length of the shadows (MS) is difficult to measure from the full lunar photograph,
but can be determined by measuring the shadow on the enlarged image and scaling it to the size of
Image #1. Now you have all the needed information to calculate the height of a lunar feature.
1. The mountains Mons Piton and Mons Pico have been identified on the magnified lunar
photograph. Measure the length of their shadows on the magnified image (Image #2) and from this
determine the length of the shadows (MS) on the full image (Image #1) using the scale of the
enlarged photo.
2. Measure the distance from the mountain’s center to the terminator from Image #1. (BT)
3. Use Equation 2 to calculate the height of the mountain (in millimeters) as it appears in Image #1.
Use the scale of Image #1 to determine the calculated height of the mountain (in kilometers).
4. Compare your answers with the known heights (Google it!)
Feature
Distance to
Terminator
(BT) (mm)
Moon’s
Radius (BC)
(mm)
Length of
Shadow (MS)
(mm)
Height (MB)
(mm)
Calculated
Height (MB)
(km)
Known Height
(km)
Mons Pico
Mons
Piton
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Image #1:
Lunar Surface at 1st Quarter
Image #2: Magnified Portion
Crater Plato
Mons Pico
Crater Cassini
Mons Piton
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