Yakima WATERS Mini Lesson
Earth’s Orbital Parameters
Targets and Assessment
WA Science Standards Addressed:
 9-11 ES2A. ES2B – Students learn what causes
climate variations on a global and seasonal scale,
investigate energy trasfer from Sun to Earth.
 9-11 INQA, INQB, INQC -- Students generate and
investigate questions, analyze the data, and
make conclusions.
Lesson Parameters
Content Area: Physics
Assessments:
 Students are first probed about their ideas of
what causes seasons. Students are then
assessed on the quality of the completed work
and their usage of classroom time.
Suggested Time: 50 min (1 class period)
Overview: Students will use globes and flashlights to
examine what causes seasons on Earth and how they have
changed over time.
Grade Level: 9th
Special Materials (per group of 6 students):
 1 globe
 1 flashlight
 4 sets diff color (~9 ea.) colored sticker dots.
Learning Outcomes:
Knowledge: The tilt of Earth’s axis (called the obliquity) and the shape of its orbit (called eccentricity)
control how much energy we receive from the sun and the seasons we experience. Students will be
able to explain that more energy is received at the equator than the poles, and how that affects
average annual temperatures.
Skill: Physically investigate changes in Earth’s orbit. Hypothesize how changes in Earth’s orbit may
influence the growth or reduction of glaciers and ice sheets.
Science Concept Background:
The tilt of Earth’s axis of rotation and the shape of its orbit control overall climate and seasons on
Earth. When the Northern Hemisphere is titled towards the sun, we receive more energy and our days
our longer and warmer. When we are tilted away it’s the opposite: shorter, cooler days. The orbital
positions in between are spring and fall. The difference in energy received from the sun at the equator
versus the poles is what drives global climate. The Earth needs to redistribute that energy, which is
why we have atmospheric and ocean circulation.
Materials (per group of 6 students):
1 globe
1 flashlight
4 sets (~12 ea.) of colored sticker dots of different colors.
Procedure:
(detailed procedure on handout)
 First probe the students about their conceptions of what causes seasons. Common
misconceptions include that the Earth is closer during the summer (it’s actually the opposite for
Northern Hemisphere) or that the Earth is facing the sun. It’s all because the Earth’s axis causes
it to be tiled towards or away from the sun during the respective summer season for a chose
hemisphere. A good probe is to ask the students to answer in their notebooks why they believe
it’s warmer during the summer than winter.
 Tell the students that they will now investigate what actually causes summer to be warmer
than winter. Hand out the worksheets and walk the students through the instructions.

Indicate that the front of the classroom with be the North Star and that their axis should always
be pointed towards the front (you may want to draw this on the board, too).
 Draw a North Star on a chalk/white board, or cut one out for the front of the room.
 Arrange students in groups of 3-6 (the worksheet says six, but this can be easily completed with
fewer students). One person will be the sun, holding the flashlight at waist level. The other
four students arrange themselves in a square facing into the sun, with one person facing away
from the North Star.
 Label these positions A, B, C, D, and they will represent positions in Earth’s orbit corresponding
to different seasons.
 Make sure students keep the axis of the Earth pointed towards the North Star.
 Have students pass the globe between positions while the Sun shines the light on the globe.
The sixth student uses the colored dots to mark the area of the most intense light on the globe
at each position (using a different color dots for A, B, C, or D).
 Students answer the questions listed on the handout.
Key questions:
1. Which orbit location produced the most direct sunlight for the Northern Hemisphere?
What season does this location represent? Orbit location C. Summer.
2. Which orbit location produced the least direct sunlight for the Northern Hemisphere?
What season does this location represent? Orbit location A. Winter.
3. How does the range of latitudes for the brightest light shift throughout Earth’s orbit? The range of latitudes
moves up and down as the year goes by, moving more northward during NH summer, and vice versa.
4. For us in Washington State, how do the length of days (amount of time receiving light
from flashlight) compare during the summer to the winter? Is that light MORE or LESS
intense during summer or winter in Washington? Explain your answer. We receive more direct sunlight
during NH summer and our days are therefore much longer. The beam of brightest light is much closer to WA
during our summer.
5. How does the intensity of light change between the equator and the poles? What affect
does that have on average temperatures (i.e. are annual temperatures greater or less at
the poles than the equator and why?) The equator receives more direct light, or more intense light.
6. If Earth were not tilted on its axis, how would your findings be different?
No seasons
7. In step 10 you changed the shape of Earth’s orbit (called its eccentricity) and made it more elliptical and less
circular. Which orbital shape do you think (more elliptical or more circular) would promote the growth of
glaciers and ice sheets? More circular. When it’s elliptical it gets too close during the summer and melts
everything away.
Extension(s):
The last orbital parameter that changes is Earth’s wobble, called the precession. Over time, the Earth’s
axis of rotation traces a circle in the sky, and thus does not always point at the North Star (in the N.
Hemisphere). You could introduce this idea and have the students experiment with how they think precession
will affect climate. Precession either enhances or mediates seasonality. If the “wobble” is pointed towards
the sun during N. Hemisphere summer, it will enhance seasonality. Conversely, if the “wobble” is pointed
away from the sun during N. Hemisphere summer it will decrease the strength of the season. All of these
changes in orbital parameters (eccentricity, obliquity, and precession) are well understood and follow very
specific patterns. In additional lessons you can introduce the periodicity of each of these (100 k, 46 k, and 23
k, respectively), and relate that to long-term climate. These are termed “Milankovitch cycles” after the
scientist who first theorized them.
Teaching Tips:
The most common misconception is that the seasons are caused by proximity in our orbit to the sun. It’s
important to make this distinction when wrapping up the lesson. You can also talk about how Earth’s orbital
cycles have changed over thousands of years (Milankovitch Cycles). Instead of having students hold the globes
(introducing a lot of error by them not holding it straight) we had some glasses set the “sun” in the middle of a
table on a stack of books and we set the globes in the four positions around the desk. You can calibrate the
height of the flashlight beam by making sure it hits the equator during the spring and fall seasons. Students
needed help understanding what was meant by “latitude range.” I instructed my students to write down the
average (just by glancing) of the maximum and minimum latitudes the dots landed on.
Supplements:
Adapted from:
http://www.teachersdomain.org/resource/ess05.sci.ess.earthsys.lp_seasons/
Wikipedia on Milankovitch Cycles:
http://en.wikipedia.org/wiki/Milankovitch_cycles
Author: Matt Jenkins, Yakima WATERS Project, CWU, Winter 2011
Earth’s Orbit and Seasons
Objective: In this activity you will work in groups of five to model the way sunlight strikes the Earth during
different times of the year, and investigate how this has changed over time.
Materials (per group of 4-6):
1 flashlight
1 globe
4 sets (~12 ea.) of sticker dots (different colors)
Procedure:
1. One student represents the Sun by holding the
flashlight at waist height. The light beam emitted
by the flashlight represents the most direct rays
of sunlight.
2. Have four students represent four locations in
Earth’s orbit by forming a square, facing inward,
around the student with the flashlight. One of the
four students should stand with his or her back to
the North Star. (The teacher will designate a place
for the North Star).
3. Designate the four students “A,” “B,” “C,” and “D.”
“A” is the student with his or her back to the
North Star. “B” is to the right of “A,” and so on.
4. The sixth student in the group acts as the recorder. One set of colored dots should be
assigned to each orbit location: A, B, C, and D.
5. Have “A” hold the globe, waist-high, with the North Pole pointed towards the North Star,
representing Earth’s tilt.
6. Shine the flashlight toward the globe. Keeping the axis pointed toward the North Star, “A”
should be able to spin the globe in place. As “A” rotates the globe on its axis to represent
one day, the recorder should mark the top and bottom of the brightest band of light
(using the assigned colored dots) around the globe. This is the latitude range of the most
direct sunlight.
7. Repeat steps 5 and 6 for the remaining three locations of Earth’s orbit, using the other
three sets of colored dots.
8. Fill in the second and third columns of the data table below: dot color and latitude range.
9. Complete the third column: season in the Northern Hemisphere.
Orbit Location
Dot Color
Latitude Range
Season in N. Hemisphere
(spring, summer, fall, winter)
A
B
C
D
10. Have student A take two steps back and student C take one small step forward. Sketch and label the shape
of the new orbit below. How would the climate be different at points A and C?
Questions (answer in your notebooks)
1. Which orbit location produced the most direct sunlight for the Northern Hemisphere?
What season does this location represent?
2. Which orbit location produced the least direct sunlight for the Northern Hemisphere?
What season does this location represent?
3. How does the range of latitudes for the brightest light shift throughout Earth’s orbit?
4. For us in Washington State, how do the length of days (amount of time receiving light
from flashlight) compare during the summer to the winter? Is that light MORE or LESS
intense during summer or winter in Washington? Explain your answer.
5. How does the intensity of light change between the equator and the poles? What affect
does that have on average temperatures (i.e. are annual temperatures greater or less at
the poles than the equator and why?)
6. If Earth were not tilted on its axis, how would your findings be different?
7. In step 10 you changed the shape of Earth’s orbit (called its eccentricity) and made it
more elliptical and less circular. Which orbital shape do you think (more elliptical or
more circular) would promote the growth of glaciers and ice sheets? Explain your answer.
8. How do you think changes in these orbital parameters could affect long-term climate on
Earth?