Many people have misconceptions about why we have seasons. The real
reason for seasons lies in the fact that the Earth is tilted on its
axis. The classic diagram of the Earth's tilt, can be found in textbooks
for elementary students and graduate students alike.
The tilt of the Earth affects the length of days and also the amount
of direct sunlight received during the seasons. As you can see, days
are shorter in the Northern Hemisphere during the winter because the
North Pole is tilted away from the sun and the Northern Hemisphere receives
less direct sunlight. Just the opposite is true in the summer, when
the North Pole is tilted toward the sun. As the Earth orbits the sun,
the Northern and Southern Hemispheres are put into and out of direct
sunlight. The part of the Earth tilted toward the sun gets more direct
sunlight than the part tilted away from the sun.
In equatorial regions, the length of days and the directness of sunlight
don't change as much. This is why the four seasons of winter, spring,
summer, and fall don't occur there. (This lesson is also available in
the Printed Teacher's Manual)
Balls of Various sizes
- In groups
of three-four, ask students to develop a demonstration to show why
the Northern and Southern Hemispheres have four seasons. Using rubber
balls or clay they should make models of the Earth and the sun. Have
other materials available, such as string, construction paper, dowels,
etc. They will need to account for the tilting of the Earth, the position
of the poles, the elliptical path of the Earth around the sun, the
spinning of the Earth on its axis and the effects of direct and indirect
light. They will need to use some means to mark the months of the
year. Have the student groups perform their demonstrations for one
activity will demonstrate how the sun's position in the sky changes
with the seasons. On the school grounds, have student pairs find a
shadow cast by something permanent, like a fence post or piece of
playground equipment. Ask them to measure and record its length and
position using a yardstick and compass. Have them predict what will
happen if they record length and position at various times of the
year. Have students measure the shadow each week at the same time
of day and graph their results.
activity will demonstrate the difference between the heat from direct
and indirect sunlight. When the sun shines directly on something it
heats it up more than if it shines on it at an angle. Students can
prove this through an experiment that uses two black pieces of tin.
Painted pie tins will work well. Set both tins in a piece of clay
out in the sun. Place one lying flat so that the sun shines directly
on it. Place the other standing vertically so that it receives very
little sunshine. After 10 minutes, ask students to feel which is hotter.
If possible, place a thermometer in the face of each tin and measure
the difference in temperature.
This! Journaling and Discussion
1. What causes shadows to get long and short? During what season will
shadows be the longest? Why?
2. Why is there no "winter" or "summer" at the equator?
3. Some people think that we have summer because the Earth moves closer
to the sun. How would you explain that this is not true?
4. How do the experiments with direct sunlight help to show why we have
spring and summer? Why do you think snow melts more quickly on land that
slopes to the south?
5. What would need to happen for the United States and Canada to experience
only summer? What would have to happen to give a "winter" to
those living near the equator?
6. What other seasons are there besides winter, summer, spring, and fall?
Where do they occur?
7. What would happen if the Earth's axis was not tilted?
Science Education Standards
Develop descriptions, explanations, predictions, and models using evidence.
and logically to make relationship between evidence and explanations.
An object's motion can be described by tracing and measuring its position
over time. (K-4)
is a major source of energy for changes on the earth's surface. (5-8)
The sun, moon, stars, clouds, birds, and airplanes all have properties,
locations, and movements that can be observed and described. (K-4)
provides light and heat necessary to maintain the temperature of the
in the sky have patterns of movement. The sun, for example, appears
to move across the sky in the same way every day, but its path changes
slowly over the seasons. The moon moves across the sky on a daily basis
much like the sun. The observable shape of the moon changes from day
to day in a cycle that lasts about a month. (K-4)
is the major source of energy for phenomena on the earth's surface,
such as growth of plants, winds, ocean currents, and the water cycle.
Seasons result from variations in the amount of sun's energy hitting
the surface, due to the tilt of the earth's rotation on its axis and
the length of the day. (5-8)