Exploring the Astronomy of the Seasons
Seasonal Shadows and Sunlight
A Schoolyard Investigation
#1 of Reasons for Seasons)
few periods over course of school year
outdoor fence post or other vertical object, sticks, stones or
chalk, tape measure or yard sticks, data
By measuring shadows from fall through spring, students discover that
1) shadows become longer as the fall season progresses, 2) shadows are
their longest on the winter solstice, 3) shadows become shorter as spring
approaches, and 4) students can predict that shadows reach their greatest
length on the summer solstice. They begin to grasp that the lengths
of shadows change as the Earth revolves around the sun, and that longer
shadows are due to the Northern Hemisphere's tilt in relation to the
sun. These observations are a building block for understanding the reasons
Start this activity in September (or any time that will allow repeated
observations over several months). Involve students in choosing an area
in the schoolyard or playground that gets a lot of sunlight. Select
a vertical object (e.g., stick, flagpole, fence post) that has a clear
area to the north so students can easily measure shadows. (You may already
have done this if you conducted the activity, Exploring
Hourly Shadows and Sunlight.)
do you think happens to shadows outdoors over the course of a year?
do the length of shadows in the winter compare to those in the summer?
have you noticed or experienced? What questions do you have about
shadows and sunlight?
students to hypothesize how long their object’s shadow will
be around the first day of fall (the equinox) and explain their thinking.
They can write down the measurement or stand where they predict the
end of the shadow will be and mark it with a stake.
- On the
fall equinox, have the class chart the date, time, and shadow length.
Older students can also track sunrise and sunset times. Students can
make their own data sheets or use the printable
Before students gather data, ask, How can we keep this
investigation “fair” as we measure the shadow from
season to season? If necessary, share one of the following examples
to spark students’ thinking: measure at same time of day,
use the same starting point (bottom of shadow of same object),
use the same measuring tool.
measuring shadows on the fall equinox, ask, How long do you think
our object's shadow will be on the winter solstice, and why?
these steps on the winter solstice and spring equinox. Note:
Because Daylight Savings Time (DST) has ended since the fall
observation, winter solstice measurements should be taken one hour
Connections — Discussion and Journaling Questions
patterns did you notice?
would you explain them?
general statement(s) could you make about shadows and sunlight?
questions do you still have?
Shadows: What to Expect
Students should discover that the shadow gets longer
in the winter and shorter in the spring. If they took a measurement
on the summer solstice, it would be even shorter. From there,
it begins to lengthen again as we head toward fall. Explain
that the sun’s rays are more direct in your location during
the summer and more angled during the winter. They’ll
have a chance to explore this later.
(For more, see Teacher
the degree and accuracy to which students are able to justify their
explanations of the changes in shadows in relationship to the sun's
a tree and a sun on a reproducible response sheet. Write in several
different months. Ask students to draw approximately where they think
the tree's shadow will fall at each month indicated.