What causes the seasonal cycle on earth?1
materials:
 1 newspaper hat per learner (See I. Day - Night Cycle, Activity #1)
 model of the sun (See I. Day - Night Cycle, Activity #2)
 model of the earth (See I. Day - Night cycle, Activity #2)
 flashlight
 a graph grid drawn on the chalkboard, or on a large paper hung in the classroom
 4 signs (winter, spring, summer, autumn) that can be hung around a learner’s neck
procedures:
 Have the learners put on their newspaper hats and stand in a circle with the sun’s
model in the center.
 Perhaps review what causes the earth’s day - night cycle, with learners explaining
in words as well as demonstrating with their bodies.
 Begin the new lesson by asking learners why it is hotter in summer compared to
winter? Why is the sun higher in the sky at noon in the summer than it is in the
winter? Overall, what causes earth’s seasons? (This might be a good written
assignment for the learners. If so, perhaps it should be un-graded, since this
would be an assessment of their understanding before the lesson. This could be
saved, and then after this lesson, it could be self-corrected by the learners.)
 Have learners share their ideas. Encourage them; if they have only a partial
understanding, or even none at all, thank them for suggesting ideas. If this is a
topic that they don’t understand well, then this is an example of why it’s good that
they’re coming to school!
 Tell the students that there are 2 FACTORS that combine together to cause the
earth’s seasons. One factor is that the earth revolves, or orbits, around the sun.
Teach the learners that -o the earth rotates about its axis, causing the day - night cycle
o the earth revolves in its orbit around the sun
o One little trick to help remember the proper use of these terms is to teach
the learners that “revolving is involving,” mean that revolution involves
another body, something to go around. The earth involves the sun when it
orbits the sun; so the earth revolves around the sun.
 Ask the circle of learners to demonstrate earth’s rotation; then ask them to
demonstrate the earth’s revolution around the sun model. (Caution them not to do
both together, right now, since they’ll get too dizzy! Concentrate on just the
revolution.)
 …and how long does it take for earth to make one revolution? (1 year, 12
months, or approximately 365 days)
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These lessons were adapted from Morrow, Cherilynn and Mike Zawaski (2000) “Kinesthetic Astronomy,
Lesson 1: Sky Time, Draft: 2” Space Science Institute, Boulder, Colorado, by B. Mayer for TWBSA; see
http://www.spacescience.org/education/extra/kinesthetic_astronomy/download.html
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Point out that they are revolving around the sun in an almost perfect circle, which
is accurate. The earth’s actual orbit is much more like a circle than an ellipse, or
oval. It is a common misconception that the earth’s orbit is an extreme ellipse.
Ask the learners where the hottest part of the earth is: (a) the northern & southern
hemispheres, (b) the equator, or (c) the north & south poles. (equator) Take time
for a demonstration to explain to the learners why this is so:
o Use the model of the earth to point out its roundness; the earth is almost
perfectly spherical. The sun’s rays hit the equator “head-on” at a 90o or
right angle, causing the equatorial area of the earth to have climate that is
hotter, on average, than higher latitudes.
o If possible, darken the classroom. Shine a flashlight “head-on” over the
graph grid.
 The light is “blasting” down at a 90o angle on the grid in a
relatively small, intensely lit area.
 This represents sunlight hitting the equatorial region of the earth.
 A lot of radiant energy is hitting per unit area.
 This is similar to the radiation hitting the equator at a 90o angle,
causing a hot climate.
o Now shine the flashlight at an acute angle to the graph grid.
 The light is coming at an angle that is less than 90o, and the light is
spread over a larger area of the grid.
 This represents sunlight hitting the temperate or polar zones of the
earth.
 There is not as much radiant energy hitting per unit area.
 This is similar to the radiation hitting at increasingly lower or more
acute angles, as one travels from the temperate to the polar zones
on earth.
Pose the question: If the earth revolves around the sun in an almost perfect circle,
then the earth is always about the same distance from the sun. In that case,
wouldn’t it be true that there would be no seasons? The poles would always have
the coldest climate; the equator, the hottest; and the temperate zones, in
between… there would be hot and cold latitudes, but no seasonal change during
the year.
So, earth’s revolution around the sun is not the only factor contributing to
seasonal change. Remember, there’s a second factor, and that factor is the earth’s
tilt. The earth’s axis is thought of as an imaginary line drawn from the North
Pole, through the center of the earth, to the South Pole. This line is not straight up
and down (compared to the plane of earth’s orbit around the sun); the axis is
tilted.
This is where an actual globe would be useful, because it is a model of the earth
mounted on a stand in such a way that the earth is tilted at the proper angle. If the
classroom does not have a globe, the teacher should hold the earth model at a tilt,
and explain to the learners that this is the correct orientation of the earth.
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Another factor to tell the learners is that there is a star in the northern hemisphere
night sky that just happens to be straight above the North Pole. Now, the star is
not right above the North Pole. The star, called the North Star, or Polaris the Pole
Star, is incredibly far away, but it is in a line directly over the North Pole. (This
particular star has not always been over the North Pole; nor will it always be there
in the future. Certainly for a long time it will be in this position.)
Pick an object on the classroom wall, like a clock, to represent the North Star.
Perhaps you could even draw a star on a piece of paper, label it the North Star,
and tape the drawing high up on a classroom wall.
Stand correctly to represent the earth, and have the circle of learners join you.
Lift one arm straight up next to your head and tilt at the waist so that your lifted
hand can point in the correct direction toward the classroom object that represents
the North Star.
Tell the learners to walk around the circle, demonstrating the earth’s revolution
around the sun, BUT they have to keep themselves, the earth, tilted in such a way
that their uplifted arm is ALWAYS pointing at the North Star. Do it with the
circle of learners; it’s not easy! At some locations around the circle (earth’s
orbit), you’ll have to bend forward; at other locations you’ll have to bend to either
your right or left.
Stop the revolution, and have learners at different parts of the circle
demonstration the proper body bending. If anyone is mixed up, this will be an
opportunity to set them right.
Maybe start the learners revolving again, to make sure they’ve got the correct
notion of the tilt.
Stop the revolution again, and explore how the earth’s tilt, together with
revolution, causes seasons:
o Review with the learners; on their hats and bodies, where is the - equator? (hatband)
 northern hemisphere? (the newspaper hat, above the hatband)
 southern hemisphere? (the head below that hatband)
 Republic of South Africa? (the eyes)
o Have the learners tilt correctly.
o On the orbit around the sun, represented by the circle, ask the learners to
identify which of their peers on the circle are the learners whose southern
hemispheres are facing toward the sun. (These will be the learners on the
circle closest to the “North Star.”)
 Is the southern hemisphere having its winter or summer?
(summer)
 Why? (because the southern hemisphere is “bulging out” toward
the sun, getting more direct, head-on radiation)
 Which season is South Africa having? (summer)
 Why? (because RSA is in the southern hemisphere)
 What months are summer months in RSA? (Dec., Jan., Feb.)
 Are summer days long or short? (long)
 Which day is the longest, and what is its special name? (December
21, the Summer Solstice)
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Hang the summer sign on a learner standing in the middle of the
“summer” group.
Ask the learners to identify which people have their southern hemispheres
facing away from the sun. (These will be the learners directly on the
opposite side of the circle from the North Star.)
 Which season are these southern hemispheres having, and why?
(winter, because the southern hemispheres are pointing away from
the sun, getting less radiation)
 Which season is RSA having, and why: (winter, because it’s in the
southern hemisphere)
 Which months are winter months in RSA? (June, July, August)
 Are winter days long or short? (short)
 Which day is the shortest, and what is its special name? (June 21,
the Winter Solstice)
 Hang the winter sign on a learner standing in the “winter” group.
Ask these learners to represent the day - night cycle during the southern
hemisphere winter. As the teacher, move to their location to do it with
them. This is a contortion feat! You must rotate, while maintaining the
axis tilt toward the North Star! But it does demonstrate the winter day night cycle for South Africa.
Move to the “summer” learners. Have them join you to demonstrate the
day - night cycle for a South African summer day….another contortion
feat!
Have the learners help you figure out which people on the circle are “in
spring” and “in autumn” for South Africa. Discuss which months these
are, the spring and fall equinoxes, what kind of weather each season has,
and what flowers are blooming or what common phenomena of nature are
well-known. Hang the appropriate seasonal signs on two learners.
Have the circle of learners revolve around the sun, saying the appropriate
season as they traverse that portion of the circle.
Now for a short while, have everyone both rotate (day - night cycle) and
revolve (seasonal cycle)!!
As a final activity, consider having the learners shuffle around the circle to
position themselves properly for their birthday. Then have everyone sing
“Happy Birthday” to themselves!