Reasons for the Seasons
Reasons for the Seasons is actually three activities in one. In Do
Shadows Change with the Seasons?, students conduct a controlled investigation
to determine the length of the sun's shadow on a fixed object (i.e., flagpole,
telephone pole, etc.) over a three-day period (one day in the fall, one in the
winter, and one in the spring). This concrete experience acts as a springboard
to the abstract understanding of the positioning of the sun and Earth as it relates
to the changing seasons. In How Do Sunrise and Sunset
Change with the Seasons?, students plot sunrise and sunset data collected
from the first day of fall, winter, and spring in order to analyze seasonal patterns.
In What Can a Model of the Earth and Sun Tell Us about the Seasons?, the
teacher uses a lamp and globe to reinforce the connection between the Earth's
tilt, its revolution, and seasonal change. The
Family Page extends this learning to the community
by providing families with challenges to explore at home.
Topics: light/radiant energy, heat/thermal energy, shadow, cycles, smog,
Ohio Academic Standards Alignment: Click here to view content standards alignment to Science for Ohio by grade level.
Time Required: 45 minutes (fall), 30 minutes (winter), 150-180 minutes (spring)
- Rotation vs. Revolution.
For the most part our solar system is a counterclockwise system. Viewed
from above, the Earth makes a complete counterclockwise rotation once in
each 24-hour period. This is why the sun "rises" in the east and not
in the west. The Earth revolves counterclockwise around the sun once
every 365 1/4 days.
- Tilt + Revolution.
The Earth's axis is tilted by 23.5 degrees (see
example). The north end of the Earth's axis is always pointed toward
the North Star as the Earth revolves around the sun. The Earth's tilt,
combined with its revolution around the sun, causes seasonal changes as
the sun's strongest rays heat the northern hemisphere, equator, or southern
hemisphere during a given season.
- Solstice vs. Equinox.
Solstice refers to the two times each year when the sun's strongest
rays are furthest from the equator. For the northern hemisphere, summer
solstice occurs around June 21st and winter solstice around December 21st.
Equinox refers to the two times each year when the sun's strongest rays
are directly hitting the equator. In the northern hemisphere, spring
equinox occurs around March 21st and autumnal equinox around September 21st.
Note: In the southern hemisphere, the seasons are reversed (i.e.,
summer solstice occurs around December 21st, etc.)
The Earth is closer to the sun in the summer and further away in the
winter. Fact: The Earth's tilt causes the sun's strongest rays
to hit at different longitudes as the Earth revolves around the sun.
The Earth's tilt also causes variations in daylight hours (more in summer,
less in winter).
The sun revolves around the Earth once each day causing night and day.
Fact: The Earth's rotation on its axis causes night and day.
The Earth orbits the sun once each day, causing night and day. Fact:
The Earth's rotation on its axis causes night and day.
The Earth's orbit is elliptical. Fact: The Earth's orbit varies
only slightly from a circle. Many 3D images of the solar system give
the perspective of an angle that enhances the 3D effect, but gives the
- Expected Results.
Expect the sun's shadow to be longest near the first day of winter and
about the same length on the first day of fall and spring. The sun's
shadow will be shortest on the first day of summer.
- Daylight hours.
Expect daylight hours to be shortest near the first day of winter and
about the same length on the first day of fall and spring. Daylight
hours will be longest on the first day of summer. (See