Summary
The activities in this lesson will help students understand how Earth's tilt on its axis changes the length of daylight
and creates the seasons.
Materials
Additional Resources
Books
The Seasons of Arnold's Apple Tree, by Gail Gibbons, ISBN 0-15-271246-1
Sun Up, Sun Down, by Gail Gibbons, ISBN 0-15-282782-x
The Reasons for Seasons, by Gail Gibbons, ISBN 0823411745
The Little Island, by Golden MacDonald and Leonard Weisgard, ISBN 0-440-40830-x
Sunshine Makes the Seasons, by Franklyn M. Branley and Michael Rex, ISBN 069004481X
The Real Reasons for Seasons, Great Explorations in Math and Science (GEMS), ISBN 0-
924886-45-5
Media
Bill Nye the Science Guy. Earth's Seasons; ISBN 1932644342 9781932644340
Background for Teachers
There are many misconceptions about what causes seasons. When
people think about Earth's revolution around the sun, many picture a
very oval, elliptical shape. Actually, Earth's orbit is a slightly elliptical
circle. Thus, the distance between the sun and Earth does not change
significantly throughout the year.
Earth spins on its axis, which is what causes day and night. The
axis is tilted so that the North Pole points at the North Star, Polaris,
all of the time. Because of Earth's tilt and revolution around the
sun, each of Earth's poles is tilted towards the sun for part of the
year. Consequently, each pole is
tilted away from the sun for part
of the year. When the Northern
Hemisphere is tilted towards the
sun, the result is more hours of
daylight and more direct sunlight.
These two factors create warmer
temperatures for the Northern
Hemisphere, resulting in the season
of summer. When the days are
shorter and the sunlight is much
less direct, it is the season of winter.
Intended Learning Outcomes
1. Use science process and thinking skills.
2. Manifest scientific attitudes and interests.
3. Communicate effectively using science language and reasoning.
Instructional Procedures
Invitation to Learn
Sing the song "Why Do We Have Seasons" with students. This is
a simple echo song to the tune of "Charlie Over the Ocean". The
teacher sings each line and the students echo back. This simple song
includes all essential elements on why Earth has seasons throughout
the year.
Instructional Procedures
Part One: The Earth's Movements
- Find an open area where all students in class can stand in a
circle so that everyone can see and hear the teacher and each
other easily.
- Show students a length of string that has been previously
measured to be about 2 meters in length. This string represents
the distance from the sun to Earth. (The average distance of
Earth to the sun is 150 million kilometers, which scientists call
an 'astronomical unit'.) Refer to the string as one astronomical
unit.
- Instruct students to stand around a central point. Choose an
object or a student to represent the sun in the center of the
circle. Students should face the center of the circle. Use the
string to help students create an even, almost circular shape
by stretching the string from the central point to each edge of
the circle. The students are now in the shape of Earth's yearly
revolution around the sun. Explain to the students that they
are modeling Earth at various points in its yearly revolution.
Ask students to explain to their neighbor and then to the whole
group the apparent shape of Earth's orbit in space. (circle)
Make a point of noticing that Earth does not appear closer to
the center point anywhere in the circle. (Actually, Earth is
slightly closer to the sun in January and slightly farther away
from the sun in June. However, these slight distances in the
huge scale of space do not make any significant differences
in Earth's temperature.) When the teacher gives the signal
to "Revolve!" the students should start walking in a counter-
clockwise motion around the classroom sun.
- Ask students to demonstrate what Earth does in space each day
by turning counterclockwise in place to show rotation. Identify
day and night by turning towards and away from the sun. Each
time the teacher says "Rotate!" from now on, students should
turn around in place once in a counter-clockwise motion.
- Have students return to their seats and record findings from the
model. Pose the following questions to the students: What was
the model trying to show? What key vocabulary words need to
be used? What does this model help us understand?
- Students should draw a picture in their science journals of
Earth's circular revolution around the sun, and define the words
rotation and revolution. Add drawings and helpful reminders to
clarify these terms.
Part Two: The Tilt
- Draw students' attention to the pre-hung poster of the North
Star (Polaris) on the wall. Ask students if they know anything
about the North Star. Explain to students that one of the
reasons the North Star stays in one place throughout the year
and can be used as a navigation tool is because Earth's axis is
always tilted towards it. Explain to students that no matter
where Earth is in its trip around the sun, the Northern Pole of
Earth is always tilted 23.5 degrees towards Polaris.
- Ask students to imagine that the upper half of their bodies
represents Earth. Next, ask students to demonstrate estimating
angles by bending their bodies at the waist to degrees called
out by the teacher. Start with 90 degrees, go to 60 degrees, 30
degrees, and 0 degrees, the angle measures used in the previous
sunray lesson. Make sure students are turned towards the
North Star as they are bending, pointing their head (North
Pole) consistently at Polaris. Last, students should demonstrate
an estimated 23.5-degree tilt towards Polaris. Agree as a group
what this tilt might look like.
- Draw students' attention back to the central object in your
model. What is the object that holds Earth in place during its
revolution? (The sun.) What force keeps Earth from flying
away into space? (The gravitational force from the sun.)
Discuss the limitations of the classroom model you are creating.
(The scale is not accurate and no energy is coming from our
classroom sun.)
- Students should draw a picture of Earth's tilt towards Polaris
in their science journal. Pose these final questions to students:
What questions do you have about Earth and the sun in space?
Where could the answers to these questions be found? Ask
students to meet in teams of three to discuss their journal
sketches and wonderings.
Part Three: The Seasons
- As the students are standing in their spots around the sun,
explain to students that the sun's energy travels through space
and reaches Earth. Ask students to demonstrate the sun's
tilt towards Polaris. What part of our circle is tilted towards
the sun in the most direct way? Having all students tilt 23.5
degrees towards Polaris and identify the students whose heads
are tilted towards the sun. This is the summer section of our
circle. Hand one student in the summer section the landmark
sign labeled "summer solstice". Briefly describe the summer
solstice (June 21st-22nd) as the longest day of the year. This is
the day when Earth receives the most hours of daylight from the
sun. The sun appears high in the sky as it makes its long trip
across the sky. What kinds of temperatures do we experience
on summer solstice? What activities would we be doing on
summer solstice?
- Go to the opposite side of the circle from the summer solstice.
Ask students to demonstrate Earth's tilt again and point out
that this side of the circle is tilted away from the sun (for the
Northern Hemisphere). Ask students what season they think it
would be if we were tilted away from the sun's energy. (winter)
Hand one student the landmark sign labeled "winter solstice".
Briefly describe the winter solstice (December 21st-22nd) as the
shortest day of the year when Earth receives the least hours of
daylight from the sun. The sun appears much lower in the sky
as it moves across the sky. What kinds of temperatures do we
experience on winter solstice? What activities would we be
doing on winter solstice?
- Ask students to infer what seasons the southern half of Earth
is experiencing during the Northern Hemisphere's summer and
winter. (The seasons are the opposite because the tilt towards
and away from the sun is opposite.) Allow time for students
to share personal experiences and connections involving time
spent in countries in the Southern Hemisphere.
- After the summer and winter solstice have been identified
and labeled, show students the landmark signs titled "spring
equinox" and "fall equinox". Explain to students that spring
and fall are in-between seasons, in which the weather is
changing from one season to another. Earth is neither tilted
towards or away from the sun during these times. Ask students
to demonstrate their tilt again, and find the areas of the circle
where students are tilted sideways, and not towards or away
from the sun. Hand one student the 'spring equinox' sign, and
another the 'fall equinox' sign on the opposite side. Briefly
explain the dates and the fact that daylight hours will be equal
on the equator during these days. If one Earth day is 24 hours,
and day and night are equal, how many hours of daylight would
Earth experience on an equinox day? Ask students to describe
first to a partner and then to the larger group the weather, signs
in nature, and activities of spring and fall.
- Many of the students are not holding signs yet. Ask students to
look carefully around the circle at the four identified seasonal
landmarks. Show students the stacks of cards labeled for the
transitional time between seasons. Instruct all students who
do not yet have a card to carefully decide which sign would
best describe the seasonal time they represent. (summer to fall,
fall to winter, winter to spring, & spring to summer) Students
should make their decision and then move to collect their sign
and return to the circle. As students hold their cards up in
front of their chests, it is easily assessed whether any mistakes
have been made and can be corrected.
- This demonstration can be quickly replicated on numerous
days throughout the school year by using the cards and a
central point. With practice, students will be able to quickly
and accurately create a model of Earth's orbit around the sun,
demonstrate earth's constant tilt towards Polaris, and identify
the seasons throughout the year.
- Students should sketch a picture of Earth revolving around the
sun with the four seasonal landmarks labeled and described in
their science journals.
Part Four: Creating a Paper Seasonal Model
- After creating the human model of Earth's yearly revolution,
students will next work in teams of four to create a smaller scale
model in which the four seasonal landmarks are identified using
the Styrofoam board and skewers from the sunray lesson, along
with four paper models of Earth.
- Students should lightly make a line diagonally from opposite
corners of their Styrofoam board to identify a central point. At
the central point, students should place a tack.
- Next, measure and cut a piece of string or yarn that
approximately 15 centimeters long. This length will represent
one astronomical unit. Poke the tack through one end of the
string and hold it in place at the center of the Styrofoam. Use
the string to guide the pencil around the central point to make
a model of Earth's elliptical, circular revolution through space
around the sun.
- Now, color and cut out the four models of Earth. Tape each
model to the end of each skewer.
- By placing a protractor on the Styrofoam, students measure
a 23.5-degree angle towards the classroom 'Polaris' and poke
the skewers into the Styrofoam in the four seasonal landmark
positions around the sun. Which Earth is tilted towards the
sun (tack in the center) with its Northern Hemisphere? Label
this skewer 'summer solstice'. Label the opposite Earth model,
which has its Northern Pole tilted away from the sun 'winter
solstice'. Review dates and attributes of these days. Have
groups identify the correct position for their 'spring equinox'
and 'fall equinox' Earth models and label them. Review dates
and attributes of these days.
- Students should write descriptive sentences about the four
seasonal landmarks in their science journals. Include the
vocabulary words direct and indirect sunlight in descriptions.
Part Five: Graphing the Sunlight
- Lay a piece 9" x 13" art paper horizontally so that it forms a
long, thin strip. Starting on one edge, measure and make a
mark with your pencil at every 3 centimeters. These marks
will be the months of the year. Label each mark with the
abbreviation of each month. The extra space at the end of the
paper will be used later as a tab to glue the paper into a circle.
- Using the Hours of Sunlight Data Chart, measure a line straight
up from each month's tick mark. Make one centimeter equal to
one hour of sunlight. After all lines are complete, connect the
tops of each line. Shade in the area below the line with a yellow
color. The shaded space represents the hours of sunlight that
Earth receives throughout the year.
- Finally, glue the edge of the paper to the opposite side to make
the paper into a circle. Stand the circle of graphed sunlight in
the center of the Styrofoam model of the seasons. As students
look at their model from the side, turn the circled paper so
that the months on the paper correspond correctly with the
models of Earth on the skewers. Ask students to generalize as a
group what they notice about how the hours of sunlight change
throughout the year and how this affects Earth's seasons.
- Students should record the hours of sunlight graphing activity
in their science journals.
- Pose questions to students for discussion and journaling: What
does your graph of the sunlight show? How does the hours of
sunlight Earth receives connect to the seasons?
Extensions
Curriculum Extensions/Adaptations/
Integration
- For advanced learners, pose 'what if' questions to students to
stimulate hypothetical thinking. What if Earth were not tilted?
What if Earth revolved every 100 days? What if Earth did not
rotate?
- For learners with special needs, ask students to create a simple
foldable which shows the position of Earth in the four seasons
throughout the year. Each picture should be labeled with the
correct heading and with at least three descriptive phrases
underneath. (summer solstice: hot, long days, more sun)
Family Connections
- Students should ask 5 adults if they can explain the real reason
for Earth's seasons. Bring data collected to school and compile
as a class the number of adults who have misconceptions. Add
this information to the classroom compare/contrast board.
- Students and families should plan a significant way to 'celebrate'
one of the seasonal landmarks. (Get everyone in your family to
say "Happy Winter Solstice!" on December 21st.)
Assessment Plan
- Students will write on an index card to explain the reasons for
seasons. Post cards on the compare/contrast board involving
accurate information and misconceptions.
- Students will make a choice from the Reasons for Seasons Choice
Board to demonstrate their scientific knowledge of seasons.
- Students will participate in a game of 'scientific pictionary' to
demonstrate key seasonal vocabulary and concepts.
Bibliography
Research Basis
Huitt, W. (2003). Constructivism. Educational Psychology Interactive. Valdosta, GA: Valdosta
State University. Retrieved [date], from http://chiron.valdosta.edu/whuitt/col/cogsys/construct.html
The constructivist approach to teaching states that when a student
feels safe and secure in his/her learning environment, the processing of
new thoughts and ideas will take place. Advocates of constructivism
state that it is the stimuli of the environment, rather than the stimuli
themselves that most greatly impact student achievement. In most
curriculums, knowledge and skills are taught separately and then
connected, versus the constructivism-oriented classroom in which
students acquire content while carrying out tasks that require higher-
order thinking. For example, scientific knowledge is usually taught
by working students through information piece by piece, rather than
looking at new knowledge from a holistic viewpoint. Teachers need
to first consider the knowledge and experiences students bring with
them to the lesson. Then, the instruction should be built so that
the students can expand and develop new knowledge by connecting
it to previous experiences and learning. Teachers should provide
a mixture of direct instruction, active practice of the new skill, and
feedback. The constructivist approach is centered on a student's
pre-existing experiences, filling the gaps and providing ample time,
space, experiences, with choice and differentiation for students to
display their new knowledge.