Sunset, and Seasons
Day Length (Photoperiod)
#5 of Reasons for Seasons)
Students track photoperiod (daylight hours) over time and predict
how daylight will change during different seasons. This helps
build their understanding that ever-changing daylight is the driving
force for migrations and all other seasonal changes.
Ask, Which season do you think has the most daylight hours?
The least? If students are stumped, ask, How do you spend
your time after dinner in the summer? In the winter? Why do you
think the amount of sunlight changes over the year? What questions
do you have? Write
students’ ideas on a chart that they can revisit and revise
at the end of this learning experience.
the class to discover how the amount of daylight changes throughout
the school year.
students to hypothesize whether the amount of daylight (called
photoperiod) will increase or decrease between fall and
winter, winter and spring, and spring and summer. Have them
explain the thinking behind their responses.
up a class chart, or have students use individual charts,
to write down the sunrise and sunset times for your location
each day, each week, or only on the equinoxes and winter
To locate these times, students can check the local paper
or use the form on this Web site: Complete
Sun and Moon Data for One Day. (Because you can punch
in any date on the form, you can jump ahead to future dates,
such as the first day of each season. This will enable you
to complete the activity in just one or two class periods.)
Older students should make charts for 2 additional locations
– one north of you and one south of you. (To make
this more engaging, try to set up an exchange with other
your students are participating in Mystery
Class, they will receive this information for 10 classrooms
hidden around the globe!
Also have students track the maximum or average temperatures
for each location. (They can locate this through the National
students have gathered the data, they should calculate the
photoperiod (hours of daylight) – and high or average
temperatures, if they have them – for each date; see
Calculating Photoperiods. Finally, they can graph their
data (see Graphing
The number and rate of changes in daylight
hours varies according to the latitude of a location.
The greatest and most rapid changes occur farthest from
the equator (at the poles). On the equator, the daylight
hours are close to equal all the time.
north of you in this hemisphere should have more hours
of daylight during the summer (between the Vernal and
Autumnal Equinox) and fewer hours during the winter
(between the Autumnal and Vernal Equinox). Those locations
south of you in this hemisphere have the opposite pattern.
The tilt of the Earth’s axis as it rotates and
orbits around the sun causes these changes in daylight
hours through the seasons.
students revisit and revise their responses charted during
Laying the Groundwork.
and Journaling Questions:
Up: Reasons for Seasons
How does what we’ve discovered through all of these
activities help us explain the changes we observe —
in weather and in living and nonliving things — from
season to season?
what students uncovered about the patterns that exist in different
seasons and what they can infer from this. In the winter,
for instance, the sun is at a lower angle and there are fewer
hours of daylight, so less heat is produced. In the summer,
the sun is more direct and there are more hours of daylight,
so more heat is produced. The increasing warmth and sunshine
of spring triggers ice melt and plant growth, which enables
the food chain to come to life and animals to migrate in search
of food for themselves and their young. They should understand
that changing sunlight is the driving force for seasons and