Download Slide 1

Journal 8/31/16
Why do you think God made the seasons? Why not have
made the world so we get fertile crops all year round?
Objective
Homework
To learn about the wobble in
the Earth's orbit
Read book section 1.4
Pages 12 - 16
Notes: The Tilt of the Earth
As we go around the sun, something causes
weather to warm up and cool down in
predictable patterns. We call this the seasons.
None of this should be new. What might be new,
however, is what causes this change.
Notes: The Tilt of the Earth
As we go around the sun, something causes
weather to warm up and cool down in
predictable patterns. We call this the seasons.
None of this should be new. What might be new,
however, is what causes this change.
The seasons are NOT caused by the Earth
getting closer and farther from the sun. (If you
put this on a test, you will get NEGATIVE points)
Rather, the seasons are caused by a 23.5° tilt of
the Earth’s rotational axis from vertical. This
causes sunlight to hit at different angles, which
gives it different strength to warm the Earth.
Notes: The Tilt of the Earth
Let’s illustrate this.
Imagine the circle below is the Earth. Sunlight
comes from the right.
A
B
C
We want to examine what’s happening with the
sunlight at points A, B, and C.
Notes: The Tilt of the Earth
Let’s illustrate this.
Imagine the circle below is the Earth. Sunlight
comes from the right.
A
B
C
At C, the sun is shining straight down. This
creates the most heat.
Notes: The Tilt of the Earth
Let’s illustrate this.
Imagine the circle below is the Earth. Sunlight
comes from the right.
A
B
C
At B, the light from the sun is hitting the Earth
at an angle. This is less efficient and less heat is
absorbed.
Notes: The Tilt of the Earth
Let’s illustrate this.
Imagine the circle below is the Earth. Sunlight
comes from the right.
A
B
C
At A, the light from the sun barely grazes past
the Earth. Almost none of it will be absorbed!
Notes: The Tilt of the Earth
So why does this cause seasons? Shouldn’t it
just mean that the farther you get from the
equator, the colder it gets?
No, because that tilt changes which way it faces
depending on the season.
Notes: The Tilt of the Earth
So why does this cause seasons? Shouldn’t it
just mean that the farther you get from the
equator, the colder it gets?
No, because that tilt changes which way it faces
depending on the season.
In summer, we here in
the US follow the path of
the dotted line over the
course of a day. You can
see that this gets us
pretty close to the
direct-sunlight area.
Thus, it gets hot.
Notes: The Tilt of the Earth
By winter, we’ve moved around to the other side
of the sun. Now we can see that sunlight hits at
only a very bad angle during the day. This
means we don’t absorb as much sunlight and
thus it’s cold.
Notes: The Tilt of the Earth
But there’s more! Not only is the Earth tilted,
but the way it’s tilted wobbles. We call this
wobble “precession”. Precession is hard to
explain, so let’s look at a visual example.
(Summarize what
you’re seeing here in
your own words.)
Notes: The Tilt of the Earth
This “wobble” in the Earth’s spin is slow. It will
take the Earth 26,500 years to wobble all the
way around just once.
As the Earth wobbles, the “north star” - the star
the axis points at changes. Right now it’s
Polaris, but back in the time of the Egyptians, it
was a star called Thuban.
Seasons Mini-Lab
We’re going to do a lab to prove how the seasons are
caused by the tilt of the sun and not by how close we are
to the sun. This is going to be done as a computer
simulation. Take close notes!
http://astro.unl.edu/naap/motion1/animations/seasons_e
cliptic.html
http://www.sepuplhs.org/students/iaes/simulations/SEPU
P_Seasons_Interactive.swf
http://astro.unl.edu/classaction/animations/coordsmotion
/daylighthoursexplorer.html
Exit Question
What would happen to seasons if the Earth's orbit were
tilted by a few more degrees?
a) There would be no seasons at all
b) The seasons would be less extreme in temperatures
c) The seasons would be more extreme in temperatures
d) The weather would change from hot to fast and back
in less time.
e) Not enough information
f) None of the above