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Light Power and seasons
Exploration Phase
What are the differences between these pictures?
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Lab Activity:
Lab Activity
Obtain a Styrofoam ball. This will represent the earth. Stick a push pin
into the “south pole” of your earth to hold it. Imagine where Kansas
City would be. For this part of the lesson, this ball will represent the
earth, and we will call it the “earth ball”.
The instructor will set a bare-bulb lamp near the center of the room and
draw a pointer that tells you the direction toward the North Star.
Q The light from the bare bulb will represent light from the sun.
Hold your earth ball so that the north end points up toward the
direction of the North Star given by the instructor. Now turn the
ball on its axis about the north pole. What happens to Kansas
City? About what fraction of the time is it lit by the lightbulb?
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Q From the observations of this activity, create an explanation
as to why we experience night and day, what causes the
appearance of a sunrise, and what causes the appearance of a
sunset? Both the sun and moon rise in the east. Using this fact,
determine and describe which way the earth rotates.
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Lab Activity:
Now, we will once again use the stryofoam ball to represent the earth. Take the
earth ball and hold it so that the north pole points toward the direction of the
North star.
Q As you spin the ball slowly, notice which gets more direct sunlight: the
area north of the equator (the northern hemisphere), the areas south of the
equator (the southern hemisphere), or neither.
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Q Find the place in the room where the north half gets more direct light
(and is warmer) while the south half gets less direct light and gets colder.
Which parts of the earth do you think are having summer and which are
having winter?
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Q Now, walk the earth in a circular path around the room with the location
of the lightbulb at the center. Be careful not to change the way the north
pole points as you go around the circle. When you are on the far other side
of the circle from the point found in the last question, which parts of the
earth do you think are having summer and which are having winter and
why?
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Thinking Activity
Q Refer back to the pictures of the earth on the cover. Describe what the
differences are in the pictures, what causes the differences, and what are
the effects of the differences.
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Concept Introduction
Q After you have seen your professor’s discussion, with your lab partner,
discuss the meaning of your observations. Resummarize your previous
writings using the new scientific terms.
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Lab Activity:
Now, we will use the orange ball to represent the earth and refer to it as the
“earth ball”. Take the earth ball and hold it so that the north pole points toward
the direction of the North star. Choose a particular place in the room, and remain
there for this activity. Mark three points on the ball. One at the equator and one
at 45o latitude north and south (halfway between equator and the poles).
Q Now, place the photovoltaic at several different locations on the earth
ball. What is the maximum current reading? At the location of the
maximum reading, what is the angle between the incoming light rays and
the direction perpendicular to the earth ball’s surface?
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Q When you place the photovoltaic on Northern 45
th
parallel on the Earth
ball, what is the current reading at noon? What is the approximate angle
between the incoming light rays and the direction perpendicular to the
earth ball’s surface?
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Q When you place the photovoltaic on the equator on the Earth ball, what
is the current reading at noon? What is the approximate angle between the
incoming light rays and the direction perpendicular to the earth ball’s
surface? Repeat this activity for the south 45th parallel, the North Pole, and
the South Pole at noon.
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Q Deduce a possible mathematical relationship between light power
absorbed by the photovoltaic versus the angle you recorded. Describe
how well your data fits the relationship that you propose.
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Q Are there any parts of the earth where the sun never sets over a 24-hour
period? Where are they, and when does this occur? Are there any parts of
the earth where the sun never rises? Where are they, and when does this
occur?
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FYI:
Besides the equator, four other lines of latitude are named because of the
role they play in the geometrical relationship with the Earth and the Sun:
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Arctic Circle — 66° 33′ 39″ N
Tropic of Cancer — 23° 26′ 21″ N
Tropic of Capricorn — 23° 26′ 21″ S
Antarctic Circle — 66° 33′ 39″ S
Only at latitudes between the Tropics is it possible for the sun to be at the
zenith. Only north of the Arctic Circle or south of the Antarctic Circle is the
midnight sun possible.
The reason that these lines have the values that they do lies in the axial tilt
of the Earth with respect to the sun, which is 23° 26′ 21.41″.
Note that the Arctic Circle and Tropic of Cancer and the Antarctic Circle
and Tropic of Capricorn are colatitudes since the sum of their angles is 90°.
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Concept Mapping Terms
Solar system, Sun , Earth , Rotation (spinning on axis), Revolution (moving
along a circular path), Seasons, Day, Night, light power, sun angle, heat,
latitude, and at least five other words.
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