All Abou

t that Ti
Sun & lt
Seasons
If the Earth had no tilt, there would be no seasons. Temperatures December
solstice
would just get colder the further you traveled from the equator.
Why is this? The Earth spins on an axis. When a basketball
player spins a ball on their finger, they are spinning it on
an axis. The axis for the basketball is vertical (straight up
and down), but Earth spins on an axis that is tilted —23.5 March September
equinox equinox
degrees to be exact. Earth’s axis always points in the
same direction. Because of this, the part of Earth that Sun

receives the most direct rays from the Sun changes as

the Earth travels around the Sun.

At the equinox, the Sun's rays shine most directly

on the equator, and the Northern and Southern
Hemispheres get the same amount of Sunlight.
June
solstice
23.5º Earth's
Axis
Arctic Circle —

Tropic of Cancer — SUN'S Northern

Equator —
RAYS Hemisphere

Southern
Hemisphere — Equator

— Tropic of Capricorn

— Antarctic Circle

During the summer solstice, the Sun shines most During the winter solstice, the Sun shines most
directly on the Tropic of Cancer, 23.5 degrees north directly on the Tropic of Capricorn, 23.5 degrees
of the equator, giving its most direct energy on south of the equator, giving its most direct energy
Earth to the Northern Hemisphere. on Earth to the Southern Hemisphere.

Vocabulary:
axis – An imaginary line that Earth spins around.
equinox – The dates when the Sun crosses Earth’s equator and the lengths of day and night are equal.
solstice – The dates when the Sun reaches its highest or lowest point in the sky at noon, marked by
the longest and shortest daylight hours of the year.

www.nasa.gov earthobservatory.nasa.gov/eokids
 WINTER & SUMMER

For geographic purposes, the Earth is divided into a When the Northern Hemisphere experiences the
northern and southern hemisphere by an imaginary blossoming of plants in the spring, plants in the
ring called the equator. Whichever hemisphere is Southern Hemisphere are turning yellow and
more directly facing the Sun during the course of the brown as fall and winter come. NASA’s satellites
Earth’s orbit will receive more of the Sun’s energy for are able to monitor these seasonal cycles.
more of the day.
Longer days mean more energy for plants to grow
and for phytoplankton to bloom. As plants grow, Vocabulary:
the land on Earth looks greener from space and the phytoplankton – Microscopic
oceans swirl with green phytoplankton blooms. plant-like animals in the ocean.

These images of global

greenness show
the seasonal “green
up” of the Northern
Hemisphere in June
and the Southern equator
Hemisphere in
December.
June
Land covered with
plants are deep green.
Water with a lot of
phytoplankton are light
bluish-green to yellow.
Grey areas are where
no data were collected
during dark months of
the year around the
poles.

equator

December

Images: NASA Earth Observatory

2
Maker Corner c ie n c e
l S h a d o w S
Season-Dia
Have you ever looked at your shadow in the middle of a bright summer day?
How about in the middle of winter? Did you notice anything different?
Our shadows grow as summer fades to winter, but why? Check out this easy
activity to see how the angle of the Sun affects your shadow.

Materials:
l protractor l paper
l 30 cm (1 ft.) of string l tape
1
l 1 container of clay l 2 pencils
l small single point flashlight

1. Tie one end of the string to the hole in the

protractor and tape the other end to the bright
side of the flashlight.
2. Place a ball of clay at the corner of the paper.
3. Stand the pencil up straight in the clay.
4
4. Complete setting up the season-dial by squishing
the protractor into the clay. Line up the pencil
with the 90° mark. Line the protractor's straight
edge with the diagonal of the paper.
5. Solve to find the noon Sun angle if you were
standing at 45° N latitude during the summer
solstice, the equinoxes, and the winter solstice.

Calculating Noon Sun Angles For example, if you were standing at 45ºN
First, find the distance in degrees between latitude, the noon Sun angle at summer
the latitude of where you are and where the Sun’s solstice would be:
most direct rays are shining on Earth at that time 45° N – 23.5° N = 21.5°
of year. Then subtract that number from 90°. 90° - 21.5° = 68.5° is the noon Sun angle

The most direct rays of the Sun are shining at: Find these Sun angles:
• 23.5°N on the summer solstice Noon Sun angle at equinoxes.
• 0° (the equator) on the equinoxes 45° N – 0° N = 45°
• 23.5°S on the winter solstice 90° - 45° = ____° is the noon Sun angle
(note: degrees latitude are negative Noon Sun angle at winter solstice.
numbers south of the equator) 45° N – 23.5° S = 68.5°
Tropic of Cancer 23.5ºN (+23.5) — 90° - 68.5° = ___° is the noon Sun angle
Equator (0º) —
Tropic of Capricorn 23.5ºS (-23.5) —
3
 What's Happening?
6. In a dark room, shine the flashlight along the
The hemisphere that is more directly facing the
string toward the pencil, making sure the Sun at a given point in Earth’s orbit receives
string lines up with your noon Sun angle for more of the Sun’s energy. When the Sun is
directly over your head, you are receiving the
each season. Mark the edge of the shadow Sun’s most direct rays. But your shadow is
on the paper, using the other pencil. shortest because it falls directly underneath
you. As the tilt of the Earth changes relative
6 Align the string to the Sun, the seasons change. On the winter
to the angle you solstice the angle of the Sun is lowest on the
calculated for the horizon, shining at you more than on you. This
noon Sun angle. is why it casts a longer shadow in winter.
For example, if you
shadow —
were standing at
45ºN latitude at the SUN'S
summer solstice,
align the string to RAYS
the 21.5º mark on
the protractor.

7. What happens to the shadow throughout

the year?
8. Repeat the experiment, but this time solve
for your latitude.

Shifting Shadows
Want to see how shadows shift depending on where What’s going on?
you are on Earth? You can try this easy experiment
with: a basketball, three paperclips, a jar, masking You just modeled an equinox. Your middle
tape, and a light or lantern. paperclip has no shadow because it is at the
equator, where the Sun’s rays are directly
First, tape a line down the center of your basketball, overhead. The top paperclip has a shadow
cutting across all the ribs of the ball. Next, tape that points north because it is in the Northern
three bent paperclips to three neighboring ribs of Hemisphere and the bottom paperclip has a
the basketball along your masking tape line. Use shadow that points south because it is in the
an open jar as a stand by placing the ball on top. southern hemisphere. Shadows can tell you
Then, turn down the lights and step back. Shine your about seasons, but also about where you are
light at the middle paperclip. What direction do the on Earth.
shadows of the other two paperclips point?

basketball—

masking paper clip

Tape— shadow —
flashlight

Taped bent
equator—
paperclips —
equator—

hadows.html
co/HTML/TG-s
jar as rium.edu/cha
a stand— tps://www.explorato
oratorium ht
d from the Expl
Activity adapte

4
Answers: Noon Sun Angle at Equinoxes = 66.5° and Winter Solstice = 43°