Lunar Cycle Lab
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The moon, like a
flower
In heaven's high bower,
With silent delight
Sits and smiles on the night.
William Blake, Night
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What is more familiar than the phases of the Moon? They are
recognized by children everywhere, but they are not necessarily
simple. There are unsuspected secrets about them that you will
discover as you work through this lab.
- Click here for a primary-school
version of this activity.
- Needed materials: bright lamp for sun, moonball (opaque golf
balls work better than translucent styrofoam ones), dark room,
red flashlight.
- Select a lab partner. Work in groups of two or three persons.
- Model every step as instructed using a moonball. Stand up and
do it! Don't just sit still and secrete answers by sheer force of
thought. The answers are not as important as the method:
learn how to use the modelling techniques to come up with reliable
answers you can have confidence in.
- Complete each step sequentially, before going on to the next.
- Do not ask for help until you have attempted to model that
step.
I. Model day and night with Mt. Nose
- Your head is the earth; the lamp is the sun; the ball is the
moon.
- Mt. Nose is located on the earth's equator.
- Anything straight ahead of you, in front of your nose, is
located on the meridian
overhead. (Pretend you are lying on a recliner looking up.)
- Extend your arms out to the side, palms forward. Anything in
front of your face or arms is visible "above the horizon."
Anything behind you is "invisible" beneath your horizon.
- You will not need to refer to north or south directions in
this lab.
- Mt. Nose turns eastward (to the left) as the earth rotates.
Stand up, face the sun, and make the earth rotate one time around,
now, in the proper direction.
- Mr. and Mrs. Epidermis live on Mt. Nose.
- Face the center lamp.
- Where in the sky do Mr. and Mrs. Epidermis see the sun?
- What time of day is it?
- Turn eastward (to the left) until your right ear is toward the
sun. Extend your arms so that your right hand is toward the sun,
your left hand pointing away.
- What time of day is it on Mt. Nose?
- Which ear or hand is the eastern horizon for Mr. and Mrs.
Epidermis?
- Which ear or hand is the western horizon for Mr. and Mrs.
Epidermis ?
(These ear-hand directions do not change: to remember them, use
labelled gloves or attach "east" and "west" stickers to your
hands if necessary!)
- What time of day is it on Mt. Nose when your back is toward
the sun?
- On what part of your head is it daytime?
- What time is it on Mt. Nose when your left hand and left ear
are toward the sun?
- STOP: Before going on to Part II,
ask the instructor or lab assistant to check your answers to this
part. Be prepared to demonstrate the sunset and sunrise
positions, and know which way is east and which way is west
for both.
II. Model the rotation and revolution of the moon
- Rotation refers to the turning of a body around its
own axis.
- How long is the rotation of the earth?
- The length of one rotation of the earth is one "earth day";
the length of one rotation of the moon is one "lunar day," and
they are not necessarily the same.
- Revolution refers to the orbit of one body around
another.
- How long is one revolution of the earth around the sun?
- The length of one revolution of the earth around the sun is
one "year"; the length of one revolution of the moon around the
earth is one "month."
- The diagram below shows the Earth and Moon as viewed from
space far above the north pole of the Earth.
- Stand in the noon position with the moon held at arm
length in the direction of the sun, as in #1. (The arrows
coming from the right represent light rays from the sun.)
- Identify a mark on your moonball (such as a sporting brand
label on a baseball or golfball) and turn the moon so that this
mark is facing you. Let the marked side always represent the
"near side" of the moon.
- At position #1, is the marked side (near side) the same as
the bright side?
- At position #1, what proportion of the near side of the
moon is illuminated? All, half, more than half, less than half,
or none?
- Move the moon to positions #2 and #3. Keep the marked side
toward you at every position.
- At position #3, is the marked side (near side) the same as
the bright side?
- At position #3, what proportion of the near side of the
moon is illuminated? All, half, more than half, less than half,
or none?
- Fill in the table below for each position as numbered in the
diagram above. Answer with the following phrases:
- A. None
- B. Less than half
- C. Half
- C. More than half
- E. All
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#
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Proportion of the Near Side of the Moon that is
illuminated
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1
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2
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**
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3
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*
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4
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*
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5
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*
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6
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*
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7
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*
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8
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*
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- The rotation of the moon:
- Procedure:
Let partner A watch the model moon from a position above its
north pole as partner B pivots in place and moves the moon
through positions #1 through #8 and back to #1 again, keeping
the near (marked) side always facing toward the earth. Partner
A will have to walk around partner B, keeping his or head above
the moon as the moon completes one revolution around the earth.
Partner B may have to squat while pivoting.
- Trade places and do it again so that both partners can
observe the phenomena.
- Interpretation:
- From position #1 back to position #1 again, how many
times does partner B observe the moon to turn around its
axis?
- Does it take 24 hours, 1 month, or 1 year for the moon
to rotate once around its axis?
- If one rotation of the moon around its axis equals one
lunar day, how many lunar days are in one month?
- Many planets have days (rotation periods) that are quite
unlike the 24-hour days we know on earth. Examine the table below
and then answer the questions listed beneath it.
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Body
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Length of Day
(Rotation period)
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Length of Year
(Revolution period)
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Earth
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24 hours
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365.26 days
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Moon
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29.5 earth-days
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29.5 earth-days
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Mercury
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58.7 earth-days
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0.24 yrs (88 days)
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Venus
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-243 earth-days (retrograde)
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0.615 yrs (225 days)
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Mars
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24 hours 30 minutes
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1.88 years (687 days)
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Jupiter
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0.410 day (9 hours 50 minutes)
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11.86 years
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Saturn
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0.426 day (10 hours 14 minutes)
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29.5 years
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Uranus
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-0.746 day (retrograde)
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84 years
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Neptune
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0.800 day (19 hours 12 minutes)
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165 years
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Pluto
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-6.39 days (retrograde)
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248.5 years
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Altair, in
Aquila
the Eagle, vertex of
summer
triangle
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6 hours
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NA
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Pulsar of Crab Nebula, in
Taurus
the Bull
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3 rotations per second
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- How many planets rotate in the opposite direction,
i.e., westward instead of eastward? (This is called retrograde
rotation.)
- Which planet's day is closest to that of the earth's?
- Which planet has a day longer than its year?
- Which planet's day is nearly a week long?
- Must the largest planets have the longest periods of
rotation?
III. Phase Definitions
What are the different phases of the moon? The bright portion of the
moon as seen from the earth changes shape as it passes through different phases.
These phases are described by the following terms:
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New Moon: all of the visible
side of the moon is dark |
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Full Moon: all of the
visible side of the moon is bright |
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Crescent: the bright
part of the moon is a crescent or thumbnail shape |
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Quarter: the bright
part of the moon is half of the visible side |
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Gibbous: the bright
part of the moon is lopsided;
more than a Quarter but less than a Full |
- Note on Quarter phases:
- A Quarter moon is often called a "half moon," but really only a quarter
of the whole moon is both visible and illuminated.
- The name derives from the fact that when the moon is in a quarter phase,
it has passed through either one-fourth or three-fourths of its monthly
cycle.
- Waxing and waning are used to describe crescent and gibbous
moons.
- Waxing: Just as a candle dipped in wax grows bigger, the bright part
of a waxing moon is growing larger from day to day.
- Waning: When the bright part of the moon is getting smaller each day.
IV. Model Lunar Phases with Mt. Nose
- Face the sun. Hold your moon directly in front of Mt. Nose as
in position 1 of the diagram below. Hold the moon below eye level
so it won't block the sun.
- What is moon's phase?
- Note that there are two circles of moons shown in the
diagram below, an outer circle to draw in and an inner circle
of half-illumined moons.
- The inner circle, as in the first diagram used above,
shows moons positioned by lines from the earth at every 45
degrees. It is as if you were viewing the earth-moon
system from space, looking down on the north pole
of the earth. This inner circle shows how the sun always
illumines half of the moon as it journeys in orbit around
the earth each month.
- The outer circle (containing moons without markings) is
for you to draw the appearance of the moon at that position
as it appears from earth. You are no longer out in
space, but on the earth looking along each line-of-sight
toward the moon.
- In the outer circle at position 1 of the diagram below,
draw this #1 phase as it appears from earth by penciling in
areas not illumined by the sun.
- Check your understanding: In the previous step did you
completely darken the outer circle at position #1? If not, ask the
instructor for assistance.
- Move the moon a little to the left (about 45 degrees) until
you observe a thin waxing crescent as in position 2 of the diagram
above.
- Turn the page counterclockwise so that when you look at the
diagram you can sight along the line from earth to the
half-illumined moon at position 2. By inspecting this line of
sight on the diagram, note that the dark side of the moon
covers more than half (but not all) of the visible or near side
of the moon. Use your observation of the moonball to determine
the precise shape of the bright part of the moon corresponding
to this position (it should appear in a crescent form). Then,
keeping the page turned so that the outer circle at position 2
is at the top, draw this phase in that outer circle as it
appears from the earth.
- Does the bright side of the moon face the sun or away from
it?
- Is the bright side of the moon on the left or right side?
- Do the horns of the crescent point toward the sun or away
from it?
- Stop: Obtain the instructor's approval before going on:
______________
- Bob Berman, Secrets of the Night Sky (pp. 137-145),
explains how the tilt of the crescent moon expresses the
seasons.
- Move the moon further to the left (about 90 degrees) until it
appears half-lit as in position 3.
- What is the moon's phase? (Don't answer "half" moon.)
- To make the moon appear more full, do you move it toward
the sun or away from it?
- Turn the page to sight along the line from earth to
position 3 of the diagram, then draw this phase as it appears
from the earth in the outer circle at position 3.
- What is the moon's phase at position 4?
- Is the bright side of the moon on the left or right side?
- Turn the page to sight along the line from earth to
position 4 of the diagram, then draw this phase as it appears
from the earth in the outer circle at position 4.
- Continue moving the moon around you until the near side (near
Mt. Nose) is fully lit as in position 5. You will have to hold the
moon above your head.
- What is the moon's phase?
- Turn the page to sight along the line from earth to
position 5 of the diagram, then draw this phase as it appears
from the earth in the outer circle at position 5.
- Is the moon on the opposite side of the earth from the sun?
- Is this a good time to observe the moon with binoculars?
(Cf. Berman, p. 52.)
- Half of the Lunar Cycle, from the New Moon to Full Moon or
vice-versa, lasts about two weeks.
- Continue moving the moon around in a complete circle to
represent another two weeks, and fill in the outer circles at
positions 6, 7, and 8.
- The complete synodic cycle averages
about 29.5 days, or one "moonth" (Old English for "month").
- Match the position number in the diagram above with the
name of each phase in the table below:
- In the waning half of the moon's cycle (Waning Gibbous,
Third Quarter, and Waning Crescent), is the left or right side
of the moon illuminated as seen from earth?
- By this means can you tell the difference between a
Waxing and Waning Crescent, or between a First and Third
Quarter?
- Interpret these lines from Christina Rosetti's
Sing-Song:
"O Lady Moon, your horns point toward the east;
Shine, be increased.
O Lady Moon, your horns point toward the west; Wane, be at
rest."
- Position the moon for a Full Moon
("opposite" the sun). Let one person hold the moon in a constant
Full Moon position while the other acts as the earth and rotates
in space. For the following questions, answer with phrases such as
"setting in the west," "rising in the east," "crossing the
meridian," or "invisible beneath the horizon."
- Assume the sunset position (see Part I). If Mr. and Mrs.
Epidermis, who live on Mt. Nose, observe the Full Moon at
sunset, where is the moon located in the sky?
- Assume the midnight position. If they observe the Full Moon
at midnight, where in the sky is it?
- Assume the sunrise position (see Part I). If they observe
the Full Moon at sunrise, where in the sky is it?
- Model each phase of the moon again. For each phase determine
the location of the moon in the sky for someone on Mt. Nose at
sunrise and sunset.
- Step 1: Let one person hold the moon in position for a
given phase.
- Step 2: Let the other assume the sunset position (remember
which hands are east and west!) and determine where the moon
would appear in the sky at sunset. Use one of the phrases A-F
as listed below. Then trade places.
- Step 3: Repeat step 2 for the sunrise position.
- Repeat steps 1-3 for each phase.
A. Above the eastern horizon
B. Above the western horizon
C. Crossing the meridian
D. Rising in the east
E. Setting in the west
F. Invisible beneath the horizon
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Location at sunrise
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Location at sunset
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1
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*
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2
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*
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3
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*
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*
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4
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*
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*
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5
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*
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*
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6
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*
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*
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7
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*
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*
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8
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*
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*
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- Which types of phases may be above the east or west horizon
at sunrise/sunset?
- Which phases may be crossing the meridian at
sunrise/sunset?
- Which types of phases may be on the east or west horizon
(rising or setting) at sunrise/sunset?
- Henry W. Longfellow wrote that:
In broad daylight, and at noon,
Yesterday I saw the Moon...
- Is this poetic account possible?
- If so, in what phases might the Moon have been?
- Some time when the moon is visible, hold a ball up in the
direction of the real moon outside (do not look at the sun!).
Light rays from the sun upon the real moon are parallel to
light rays from the sun upon the moonball.
Predict: Will the moonball model and the moon show the
same phase?
- If the moon is visible all night long, in what phase is
it?
V. Model Eclipses with Mt. Nose
- Face the sun with your moon between Mt. Nose and the sun.
Stand several steps back from the sun, and make sure the moon is
much closer to the earth than it is to the sun.
- What phase is the moon in?
- Can your lab partner see the moon's shadow on your face?
Can you see a shadow on the face of your lab partner?
- Is the moon's shadow on your face (the earth) as large as
your face (the earth itself)?
- Eclipses are named for
the body that is hidden; in a lunar eclipse the moon is
obscured, and in a solar eclipse, the sun is covered. Do Mr.
and Mrs. Epidermis on Mt. Nose see a solar eclipse or a lunar
eclipse?
- Do the Chin children or the people in Eye City see an
eclipse?
- Why is an eclipse of this type not seen by everyone on the
near side of the earth?
- Why does an eclipse of this sort not happen with every New
Moon?
- Turn your back toward the sun and move the moon into the
shadow of your head on the far side from the sun.
- What phase is the moon in?
- Is this a solar or a lunar eclipse?
- Can you see the shape of your head when the moon moves into
eclipse?
(When the moon is eclipsed the earth always projects a curved
shadow. Does this prove that the earth is spherical?)
- Is this kind of eclipse visible from the entire night side
of the earth?
- Why does an eclipse of this sort not happen with every Full
Moon?
- During solar and lunar eclipses the sun, earth, and moon lie
in a straight line, but they are not arranged in the same order.
- Which body lies in the middle for a solar eclipse?
- Which body lies in the middle for a lunar eclipse?
- In the Hebrew calendar each month began with a New Moon.
Christ was crucified soon after the Passover meal, which was
celebrated in the middle of the month of Nissan. During the
crucifixion of Christ the sky became darkened. Given this
information, would it have been possible for the darkening to have
been caused by a solar eclipse?
- How does the Man in the Moon cut his hair?
Answer
VI. Conclusion: Lunar Phases, basic principles
- Does the moon shine by its own or by reflected light?
- How much of the Moon is illuminated by the Sun?
- Are the phases of the moon caused by the earth's shadow
blocking light from the sun?
- Is the far side of the moon the same as its dark side?
- What is the moon's phase when it is visible and closer to the
sun than we are?
- Does the lighted side of the moon face toward or away from the
sun?
- Does it take a day, a week, a month, or a year for the moon to
return to the same phase, e.g., from one New Moon to the next New
Moon?
- The moon falls behind the fixed stars along the zodiac just as
the sun falls behind the fixed stars along the ecliptic. Which
falls behind more quickly, the sun or the moon?
- The altitude of the Full Moon at
midnight on the meridian is opposite the altitude of the sun on
the meridian at local noon. That is, in winter the sun is low, and
the Full Moon is high, but in summer the sun is high and the Full
Moon is low.
- On what date and time would you see the Full Moon at its
highest in the sky?
- Click here for a poetic
evocation and celebration of moonlight.
VII. Discussion: How does the Earth appear from the
Moon?
You live in a colony on the near side of the moon and observe the
earth to be about four times larger in the lunar sky than the moon is
in the earth's sky. Use the ball to represent the earth instead of
the moon, if necessary, to answer the following questions.
- Does the earth shine by reflected light from the sun?
- What makes our daytime sky blue?
- Is the daytime sky on the moon blue or black?
- Does the earth show phases? All phases from New to Full?
- Which phase is the earth in as seen from the moon when the
moon is in any given phase as seen from earth? (Cf. Berman, p.
142.)
- Does the earth move across the lunar sky like the moon moves
across the earth's?
- Does the moon complete one of its major motions in 24
hours?
- Is the earth's altitude above the lunar horizon fixed in
place throughout a 24-hour period?
- How long is a lunar day? Does it equal a day on earth, a
month, or a year?
- If you were to drive the Apollo lunar rover over the surface of the
Moon, could you outrace the advance of the sun on the moon's surface?
(Cf. Berman, p. 53.)
- Your friend at Norman, Oklahoma, observes a lunar eclipse. From the near
side of the moon at the same time, what do you see?
- (You could model this by letting the ball be the earth, and
your eye be the moon.)
- If you haven't done so already, while the lab is still fresh
in your mind read the assigned texts listed below.
- Bob Berman, Secrets of the Night Sky, chs.
"Moonstruck," "Everything you never thought to ask about the
Crescent Moon," "Eclipsing it all," and "Harvest Moon."
- Michael J. Crowe, Theories of the World, pp. 10-15.
- Answer Key for this lab