1. Earth’s Rotation, Tilt, and Seasons
By the end of this class, you should be able to answer the following questions
Why do we get different seasons in the year?
What is the summer and winter solstice and how are they different in the southern hemisphere?
CAN YOU ANSWER EITHER OF THESE QUESTIONS ALREADY?

2. Earth’s Rotation, Tilt, and Seasons
Does the Earth Spin?
HOW DO YOU KNOW?
The Earth spins from west to east,
taking 23 hrs, 56 min., and 4 s.
to complete a full rotation.
Earth’s rotation results in
day and night (sunrise in the east
and sunset in the west)

3. Earth’s Rotation, Tilt, and Seasons
Earth’s Tilt
Earth does not rotate in an upright position
It is tilted 23.5° on its axis (imaginary line through from pole to pole)
Due to this tilt, the Sun strikes the Earth at different angles during its annual journey around the Sun.

4. Earth’s Rotation, Tilt, and Seasons
Earth’s tilt and revolution result in our different seasons
• When the Earth is tilting towards the Sun, the Sun’s rays reach the Northern hemisphere more directly and intensely (summer).
• At the same time, the Southern hemisphere is tilted away from the Sun so that the Sun’s rays are hitting the Earth at more of an angle and are less concentrated (winter).
The changes in temperature in Earth’s seasons are NOT caused by the Earth getting closer to / further from the Sun
(in fact the Earth is furthest from the Sun during July)

5. Earth’s Rotation, Tilt, and Seasons
• When the North Pole is tilting away from the Sun, the Northern Hemisphere experiences winter and the Southern Hemisphere experience summer.
• At the Equator (imaginary line around the middle of the Earth), the Sun’s rays strike the surface directly all year long so the seasons are less distinct.

6. Earth’s Rotation, Tilt, and Seasons
Solstices
In the northern hemisphere…
Summer Solstice is the longest day of the year. (around Jun. 21st)
It is the point in the Earth’s orbit when the Sun’s path is at its highest
Winter Solstice is the shortest day of the year. (around Dec. 21st)
It is the point in the Earth’s orbit when the Sun’s path is lowest on the horizon
In the southern hemisphere…
The opposite occurs - dates above are reversed.

7. Earth’s Rotation, Tilt, and Seasons
In the far north, due to the axis tilt of the Earth…
During the summer solstice, the Sun does not set below the horizon
During the winter solstice, the Sun does not rise.

8. Earth’s Rotation, Tilt, and Seasons
Did we get there…
Can you…
Describe why we get different seasons in the year.
What is the summer and winter solstice and how is it different in the southern hemisphere?
Assignment: Seasons on Earth