Name
Date
Class
Lab Investigation
Reasons for the Seasons
Reviewing Content
There are two main reasons for the seasons. The
first is that Earth is tilted on its axis. This tilt
causes sunlight to strike different parts of Earth
in different ways. Sunlight hits Earth’s surface
most directly near the equator. Near the poles,
the sunlight strikes at a very shallow angle. The
second reason for the seasons is Earth’s orbit
around the sun. As Earth moves around the sun,
the north end of its imaginary axis is tilted away
from the sun for part of the year and toward the
sun for part of the year. As a result, most places
on Earth have four distinct seasons: winter, spring,
summer, and autumn.
Reviewing Inquiry Focus
Models are often used in science to visualize processes or events that
cannot be directly observed. Scientists use such models to make inferences
about these processes or events. An inference is a possible explanation
that is based on fact or observation. Because we currently cannot actually
observe Earth’s orbit around the sun from elsewhere, scientists have made
models to study this movement. In this Lab Investigation, you will make
a model that will allow you to see how the sun shines on Earth as Earth
makes its orbit around the sun. You will be able to make conclusions based
on your observations about the seasons that most of Earth experiences.
In this investigation, how will you model Earth and the tilt on its axis?
How will you model the sun in this investigation?
What types of inferences will you be able to make about seasons on different parts
of Earth?
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EARTH IN SPACE
Name
Date
Class
Reasons for the Seasons
Problem
INQUIRY FOCUS
Make Models,
Observe, Infer
How does the tilt of Earth’s axis affect the light received by
Earth as it revolves around the sun?
Materials
Procedure
books
flashlight
masking tape
paper
pencil
protractor
toothpick
acetate sheet with
thick grid lines
drawn on it
plastic foam ball
marked with poles
and equator
metric ruler
1. Make a pile of books about 15 cm high.
2. Tape the acetate sheet to the head of the flashlight.
Place the flashlight on the pile of books.
3.
Carefully push the pencil into the South Pole of the
plastic foam ball, which represents Earth.
4. Use the protractor to measure a 23.5º angle to represent
the tilt of the axis of your Earth away from your “flashlight
sun,” as shown in the top diagram. This position represents
winter in the Northern Hemisphere.
5. Hold the pencil so that Earth is steady at this 23.5º
angle and about 15 cm from the flashlight head. Turn
the flashlight on. Dim the room lights.
6. The squares on the acetate should show up on your
model Earth. If the squares are not clear, move the ball
closer to the flashlight or dim the room lights more.
Observe and draw the shape of the squares at the
equator and at the poles.
19
EARTH IN SPACE
Name
Date
Class
Lab Investigation
REASONS FOR
THE SEASONS continued
7. Carefully stick the toothpick straight into your model Earth about halfway
between the equator and the North Pole. Observe and measure the length
of the shadow of the toothpick. Record your measurement on the line below.
______ cm
8. Without changing the tilt, turn the pencil about 90° (a quarter turn) to rotate
the model Earth on its axis. Observe the length of the toothpick’s shadow and
record it on the first line below. Rotate the model Earth 90° two more times.
With each turn, measure and record the length of the toothpick’s shadow below.
______ cm ______ cm ______ cm
9. Now tilt your model Earth 23.5° toward the flashlight, as shown in the diagram
below. This position models summer in the Northern Hemisphere.
10. Observe and draw the shape of the squares at the equator and at the poles.
11. Repeat Step 8 to observe how the toothpick’s shadow changes in summer.
Continue to rotate the model Earth and note how the toothpick’s shadow changes.
With each turn, measure and record below the length of the shadow.
______ cm ______ cm ______ cm ______ cm
20
EARTH IN SPACE
Name
Date
Class
Lab Investigation
REASONS FOR
THE SEASONS continued
Analyze and Conclude
Make Models When it is winter in the Northern Hemisphere, which
areas on Earth get the most direct sunlight? Which areas get the most
direct sunlight when it is summer in the Northern Hemisphere?
Observe Compare your observations of how the light hits the area
halfway between the equator and the North Pole during winter (Step 7)
and during summer (Step 11).
Infer If the squares projected on the ball from the acetate sheet
become larger, what can you infer about the amount of heat distributed
in each square?
Predict At what time of year will the toothpick’s shadow be longest?
When will the shadow be the shortest?
21
EARTH IN SPACE
Name
Date
Class
Lab Investigation
Reasons for the Seasons
Draw Conclusions How are the amounts of heat and light received in
a square related to the angle of the sun’s rays?
Interpret Data Which areas on Earth are consistently coolest? Which
areas are consistently warmest? Why?
Summarize Describe what you learned in this lab about what causes
seasons and what questions you still have.
What I learned
What I still want to know
Relate Evidence and Explanation Use your observations and results to write an
original paragraph that describes the orientation of Earth relative to the sun when it is
winter and summer in the Southern Hemisphere.
22
EARTH IN SPACE
Name
Date
Class
Reasons for the Seasons
Problem
INQUIRY FOCUS
Make Models,
Observe, Infer
How does the tilt of Earth’s axis affect the light received by
Earth as it revolves around the sun?
Materials
Design an Experiment
books
flashlight
grid transparency
pencil
protractor
toothpick
foam ball marked
with poles and
equator
marker
metric ruler
1. You have probably noticed that during winter, the sun
is much lower in the sky and average temperatures are
considerably lower than during summer. What is the
connection between the angle at which sunlight strikes
Earth’s surface and the temperature on Earth’s surface?
Imagine that you have to explain this connection to
someone who is convinced that winter in the Northern
Hemisphere is colder only because the days are shorter
and there’s less sunlight in general.
2. Your teacher will provide you with a flashlight and a
special transparency with a grid on it. The grid on the
transparency will help you visualize what happens to
sunlight when it shines on a surface at an angle. You will
also be given a foam ball and pencil to make a model of
Earth on its axis. The toothpick can be used as an object
to cast shadows on the Earth model. You will use the
protractor to tilt the Northern Hemisphere both 23.5º
away from the sun and 23.5º toward the sun to model
sunlight during the different seasons.
3. Gather your materials and design an experiment
to determine how the tilt of Earth’s axis affects the
way sunlight strikes different parts of the Northern
Hemisphere during summer and winter. Consider the
following questions as you design your experiment:
a. When the North Pole is tilted away from the sun,
what season is it in the Northern Hemisphere?
What season is it when the North Pole is tilted
toward the sun?
b. Using the flashlight, how can the projected pattern
of the gridlines on Earth demonstrate what happens
when light hits a curved surface at an angle?
c. How do shadows cast by objects on Earth’s surface
help demonstrate the connection between the tilt
of the axis, seasons, and higher temperatures on
Earth’s surface?
23
EARTH IN SPACE
Name
Date
Class
Lab Investigation
REASONS FOR
THE SEASONS continued
4.
Use the notepad below to describe your procedure and record your
observations. Be sure to include sketches that show how the modified flashlight
projects the gridlines onto the Earth model when the model’s axis is tilted away from
the source of light and when it is tilted toward it. Have your teacher review your procedure
before you begin. CAUTION: Do not shine the flashlight into your eyes or
anyone else’s.
Procedure
24
EARTH IN SPACE
Name
Date
Class
Lab Investigation
REASONS FOR
THE SEASONS continued
Analyze and Conclude
Make Models Use your model to show that when the North Pole
is not tilted toward or away from the sun, sunlight hits both hemispheres
equally. How does the distribution of the sun’s rays near the equator
differ from the distribution of the rays near the poles? How does this
relate to the temperature in these areas? How did your model capture
this difference?
Interpret Data When both hemispheres are receiving the same
amount of sunlight, what seasons is Earth experiencing? What is the
term that describes this event?
Draw Conclusions When the Northern Hemisphere is tilted away
from the sun, describe what happens to sunlight that strikes the high
latitudes in the Northern Hemisphere, and explain how this relates to
the arctic climate during winter.
Infer The lengths of shadows can give some clue about what season it
is and how far the object is from the equator. Where on Earth would
shadow lengths change the least from season to season? Explain.
25
EARTH IN SPACE
Name
Date
Class
Lab Investigation
Reasons for the Seasons
Design an Experiment What did you find difficult about this activity
given the materials you had to work with? How would you improve
upon your Earth/sun model?
Infer What would be the effect on the seasons and the hemispheres if
Earth were not tilted on its axis? Explain.
Summarize Describe what you learned in this lab about what causes
the seasons and what questions you still have.
What I learned
What I still want to know
Redesign Revise your model set-up, or use diagrams or computer art software,
to show how the tilted axis of Earth and Earth’s orbit around the sun produce
the seasons as we know them. Design your demonstration for an audience in the
Northern Hemisphere. Be sure to mark or discuss the following:
• winter and summer solstices
• autumnal (fall) and vernal (spring) equinoxes
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EARTH IN SPACE