Warm-Up
March 15
Why do we have days?
We have day and night because
the Earth rotates on its axis.
By the way . . .
When where you are is pointed toward the Sun, it
is day. Then the Earth rotates you away from the
Sun, and it is night.
Sunlight
Sunlight
Daytime
Nighttime
Learning Standard: Today I’m creating a model
to show the tilt of Earth on its
axis because it explains what
causes seasons.
Opening: Luck of the Draw (questions about seasons)
Work Session:
Notes about seasons
Cut and paste activity - seasons
Closing: Homework – Seasons worksheet
What is a season?
One of the major divisions of the year, generally
based on cyclic (recurring) changes of climate.
Spring, Summer, Fall, and Winter
Occurs in both the Northern and Southern Hemispheres
(just at different times of the year).
Seat
20
What causes the seasons?
The earth is tilted on it’s
axis at 23.5˚.
Seat 2
What’s the difference between
rotation and revolution?
Revolution is when one object orbits
another.
Rotation is when an object turn
around.
Seat 12
Before we continue, let’s review
Important Latitudes to remember
Why is earth tilted at 23.5°?
• No one knows…
• Astronomers have different theories:
– About 5 billion years ago, when the Earth was still very young, it
was struck by a Mars-sized planet. This impact could have
tipped our planet over.
– As the cloud of dust and gas collapsed when the universe was
forming, the solar system did not form uniformly, the spinning of
the gases and other planets is what made each different, hence
the tilting of the planets
– Essentially, the numerical value of this axis tilt is an artifact of
the way the Earth formed. It didn't have to have any specific
value, and in fact the other planets all have different axis tilts
owing to the differing details of their formation.
What would happen if earth
wasn’t tilted?
• Earth is tilted at 23.5 degrees, Uranus is tilted at
about 98 degrees
• If you were standing on Uranus (if you could) the only
difference you would notice was that the sun and the
other planets would appear to rise and set in the north
and south rather than east/west like on Earth.
• Whatever the reason, it's a good thing - if the Earth did
not tilt, countries near the poles would be cold and dark all
year round. If it tilted too much, the seasons would be
very extreme – like on the planet Uranus. Here the winter
lasts for 42 years in total darkness
http://www.madsci.org/posts/archives/nov99/943922199.Es.r.html
What does the tilt do?
• It allows the sun’s
rays to shine more
directly and for
longer periods of
time on some
locations than
other places of
Earth.
Who gets the most sun?
Sun Over Equator
(March 21)
Sun Over
Tropic of
Cancer
(June 21)
Sun Over Tropic
of Capricorn
(December 21)
Sun Over Equator
(September 21)
Sunlight Reaching Earth at…
• Winter
Solstice
•
Longest day
of the year in
the Northern
Hemisphere.
Shortest day
of the year in
the Southern
Hemisphere.
Tilt of Earth and Days
• The length of a day changes because the earth
spins at a tilt and the Sun’s rays hit the earth
more directly at different times of the year.
Summer solstice (June 21)
Northern Hemisphere - The day is longer than 12 hours
Southern Hemisphere - The day is shorter than 12 hours
North Pole has a 24-hour day
South Pole has a 24-hour night.
What happens during the Equinox?
Latin – equal)
The day and night have an EQUAL amount
of sunshine.
The Sun’s rays hit the earth more directly
at the equator.
Word Bank for homework
• Sunlight
Summer Solstice
Length
• Revolution
Closer
Longer
• September 22
More time
Spring
• Southern
Away
Indirect
• Autumn
Directly
Nights