Overview:
Seasons are caused by the rotation of the Earth tilted on its axis and the planet’s
revolution around the Sun. When a hemisphere experiences summer that hemisphere is
receiving more incoming solar radiation or insolation, than the other hemisphere. The
total energy received is a result of two factors. First, the sunlight is striking the surface
more directly. Secondly, the length of the day is longer, thus extending the time of
exposure to the Sun’s radiation.
Key Concepts:
In this lesson, students work through a series of activities to help understand how the
length of day changes seasonally and how the extremes at the poles affect the people who
live there.
Time:
2, 45-50 minute class periods
Materials:
Globe
Strong light source: overhead projector or light fixture
String
Pea-sized balls of modeling clay (7)
Sponsored by:
National Science Foundation
(NSF Award 0732793)
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Content Background:
For the Northern Hemisphere, the winter solstice is the shortest day of the year. In the
Arctic, the days gradually grow shorter between June and December until the far North
plunges into the complete darkness of winter. The trend reverses at Winter Solstice, the
point during the year when the Northern Hemisphere is tilted the farthest away from the
Sun. After the solstice, which falls on December 21 or 22 every year, the days begin to
lengthen. Since the day marks the beginning of the return of the Sun, many cultures
celebrate a holiday near winter solstice including Christmas, Hanukkah, and Kwanzaa.
NASA images courtesy Takmeng Wong and the CERES Science Team at NASA Langley Research Center.
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Aim:
What are the winter and summer solstice?
Objectives:
Students will be able to:
• visualize the Earth-Sun position related to the polar 24-hours of daylight
(summer) and 24-hours of night (winter).
• explore the comparative length of day at different latitudes during the
various seasons.
• explain seasonal change in terms of the intensity of solar radiation and
the Earth’s tilt.
• understand that distance to the Sun has nothing to do with seasons.
• label each season in a diagram of Earth’s revolution around the Sun.
• gain an appreciation for living in the Arctic and Antarctic during winter
and summer solstice.
Activities:
Part 1: Visualizing the Midnight Sun
Show students the time-exposed shot for
Nunavut’s Baffin Island. Do not include the
photo caption.
Teacher Tip: Explain to students that
time-lapse photography allows us to see
an event that happens over a long period
of time. Pictures are taken of the same
scene at regular, timed intervals
from the same viewpoint.
Caption: The midnight
Arctic sun never strays from
the horizon in this timeexposed shot of Nunavut's
Baffin Island. Some parts of
Nunavut endure 24 hours of
light from late April until
late August and 24 hours of
darkness from late October
until mid-February.
A time-lapse shot of Nunavut’s Baffin Island
Credit: National Geographic
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Discussion Questions:
Explain what this photo shows about the Sun at this time of year in Baffin Island.
The sun never sets; it just moves along the horizon for the twenty-four hours of the
day.
Predict the time of year represented in this photo. Explain your answer.
This is the time of the midnight sun. The time is from late April to late August with
the longest day falling on the summer solstice, June 21. For evidence, students
should note that the sun appears to move laterally rather than overhead.
Write a reflection paragraph about how you think you might feel living for months
with 24 hours of sunlight or 24 hours of darkness.
Answers will vary.
Part 2: Measuring Seasonal Changes in Day Length
Teacher Preparation:
•
Set up a globe of the world and a strong light source like an overhead projector as
the Sun. NOTE: Conduct this activity in a darkened room.
•
Place a light source on a flat desk or
table in the center of a floor space to
represent the "Sun." Around the
"Sun" table, place another flat desk
in each of the four seasonal
positions. Make sure the
tables/desks are at the
same height.
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Winter Solstice Directions:
1. Holding the globe on a stand at a 23.5º tilt, ask student’s how to position the globe so
that it is in the ‘WINTER’ position.
Students should tell you to hold the globe so that the Southern Hemisphere goes
toward the light in the center.
2. Place small balls of clay as markers along the 75oW longitude line at the 67oS, 60oS,
23.5oS, 0o, 23.5oN, 60oN and 67oN latitude points. Note the clay balls must be small
enough to pass under the globe’s support system.
3. Walk the globe around the Sun keeping its axis in the same orientation while you walk.
Ask students, “If we were to draw a line from the Earth’s axis straight into space, what
would we hit?
Students may or may not know that the North Star is directly in line with the Earth’s
axis.
4. Tell students: “Focus your attention on the two poles. As I rotate the globe one full
24 hour rotation, notice the total daylight at the South Pole and total night at the
North Pole. Also notice that the 67oS marker which lies just inside the Antarctic
Circle will receive 24 hours of sunlight and the 67oN marker (just inside the Arctic
Circle) will receive 24 hours of darkness. This position represents December 21, the
time of the Winter Solstice.”
5. Ask students: “Which clay marker will experience the longest and the shortest days.”
Students’ predictions may vary but the most accurate prediction will select the most
southern marker to experience the longest day and the most northern marker to have
the shortest day.
6. Position the globe so the 75oW longitude line is on the night side of the globe.
Ask students, “Describe which continents are experiencing day and which are
experiencing night in this position.”
Depending upon the exact position of your globe,
different continents will be illuminated with
Teacher Tip: To determine
“daylight” but North and South America should be
which way to rotate the globe,
in the dark; China and Australia should be
remember that Florida (eastern
illuminated.
USA) will always move into
7. Tell students: “Focus your attention on the 75oW
longitude line. Identify the moment when dawn
starts at one of the clay markers on that line.”
the sunlight before California
(western USA) does.
8. Slowly rotate the globe in a counter-clockwise
direction until students see the light reaching a clay
marker. (The 60oS marker will be the first to receive the light. If your globe and light
are properly positioned, the 67oS marker will receive 24 hours of sunlight.) Tell
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students: “This is dawn at the 60oS location and that all other points north of this
location along the 75 oW longitude line are still experiencing night.”
9. Continue rotating the globe, noting when each clay marker passes into daylight.
10. Refocus student attention on the whole 75oW longitude line. Ask students:
“Which marker will move into dusk first?”
Students should predict the 60oN marker.
11. Continue slowly rotating the globe until the entire 75oW longitude line has moved
into the dark, nighttime position. Ask students: “Draw a conclusion about the relative
length of day for each latitude position along the 75 oW longitude line.”
Students should conclude that in the Winter Solstice position, the southern latitudes
experience longer days than the northern latitudes.
Summer Solstice Directions:
1. Position the globe in the summer solstice position. Remind students that the
orientation of the axis must be the same as it was in the winter solstice position.
2. Position the longitude line with the clay markers in the nighttime orientation and
follow the same steps used in the winter solstice investigation to determine length of
day at the different markers.
Discussion Questions:
When did the southern hemisphere experience longer days than the northern
hemisphere?
In the winter solstice position the southern hemisphere experienced longer days
than the northern hemisphere did.
During the Summer Solstice, how did the length of day at the equator compare to
the length of day at 60 degrees north?
The equator had shorter day lengths.
Did all areas within the Arctic Circle have 24 hours of darkness during the Winter
Solstice? Explain your answer.
The Arctic Circle (67oN) marks the edge of the area around the North Pole that
experiences 24 hours of darkness. The latitudes even slightly closer to the equator
would see the sun appear low on the horizon for a few hours before it set again.
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Part 3: Solstice in the Arctic and in the Antarctic
Directions:
1. Go to Resources on the SPRINTT website and
login.
2. Select Phase II.
3. Select Exploratorium's Earth and Moon
Viewer.
4. Students can view a map of the Earth showing
day and night regions in real time.
Screenshot of the Earth Moon Viewer
Credit: John Walker
5. Explore and discuss the image emphasizing the
areas of daytime and nighttime. Make note of
the data for the Polar Regions as well as your home area.
6. Switch from “Now” to UTC (Universal Time) and Type in 2007-12-21 to see the
image for the 2007 Winter Solstice.
7. Type in: 2007-6-21 to see the image for the 2007 Summer Solstice.
Discussion Questions:
Compare the image presented in the Earth and Moon Viewer to the information
you explored in Parts 1 - 3 of this activity. Did these new images support or dispute
the ideas you developed in the earlier sections? Explain your answer using
evidence.
Answers will vary.
How did the tilt of the axis affect the seasonal day length changes you have
observed?
Due to the tilt of the axis, the northern hemisphere either receives more or less
direct as Earth moves through its orbit. When it receives more direct radiation, the
light is not only more concentrated, but it is also shining for a longer portion of the
day.
How do you think the differences in length of day / night affects the plants and
animals that live in the areas?
Students may choose to discuss the differing light needs of various plants,
hibernating animals, and the affect that longer days would have on the overall
temperature of an area.
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Part 4: How the Arctic people cope with 24 hours of light
and dark
Directions:
1. Go to Resources on the SPRINTT website and login.
2. Select Phase II.
3. Select Native Peoples Photo Gallery.
4. Direct student attention to the Location Map showing
where the various native peoples live.
Screenshot of the
Native Peoples Photo Gallery
Credit: Bryan & Cherry
Alexander Photography
5. Help students visualize the Arctic lifestyles by
reviewing some of the photos in the sections:
Greenland Inuit Winter, Greenland Inuit Summer,
Nenets Winter and Nenets Summer. Explore some of the other sections if time
allows.
6. Discuss the clothing, homes, and activities shown in these photographs and relate
them to the challenges the native peoples face living in the Arctic.
Assessment:
Students will complete the following table using what they have learned in this lesson.
Living in the Polar Regions: Long Days & Long Nights
Something new I have learned
about the seasons
Thoughts about the Native
Peoples and the challenges of
living with Long Days & Long
Nights
Something I thought I knew
that is true or false based on
this lesson.
1.
1.
1.
2.
2.
2.
3.
3.
3.
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