Hi, I am Jared, welcome to Fun Science Demos The big idea today is actually a
question.
Why do we have seasons? Well, a lot of
people think it is
because the earth is closer to the sun.
Through science we have discovered that is
really not the reason at all.
The reason is pretty simple-the earth is tilted.
I put this pencil here to show you the axis-
that is not really there in space-
but the earth is tilted. In one of our other
science videos we demonstrated
that we have day and night because the
earth spins. Seasons,
a different story, a different
demonstration. Set the earth over here.
So let us take a look at the tilt. It
takes the earth one whole year
to travel around the sun, but look at the
tilt:
June, September,
December, March down there, the tilt
stays the same as the earth travels
around the sun throughout the year.
Now, let us get back to the demonstration
and show you what happens to the
sunlight and
explain why we have seasons. So we have
changed the room and we only have our
sun
shining on our earth. And right now, it is
tilted
away from the sun-the top half of the
earth is tilted away from the sun-
and we have December. I also have this
weird metal strap with holes in it.
Now here is the important part, each one
of these holes in the same size which
means
they let the same amount of light
through each hole.
Now we check this out. Let us watch
what happens when we put the strap up. We
can see the sunlight shining through the
holes,
but something is different on our earth. So
take a look at our dots.
They are all different sizes as we go
up the globe. Why?  What is going on? Well,
the same amount of light
is getting through each hole, but the holes look different. Well,
that means the light is more
concentrated
and the earth underneath that is warmer.
But as I go up,
you can see the light is spread out, it is
not as focused, its not as concentrate up
here,
because it is tilted away from the sun.
That means the earth underneath that is
cooler;
we have seasons. And you can see the
middle part of the earth pretty much gets
concentrated sunlight
all year. Now we have moved the earth to
its June position, six months later.
Notice the tilt of my earth is still the
same.
But watch what happens with the sunlight.
I put my strap up and take a look at the
circles of sunlight.
Where in December it was once spread out-
the sunlight was spread out which means it
was cooler-
now in June you can see the circles are
much more concentrated. The sunlight is
more concentrated which means
it is warmer. Winter, summer...
seasons. Science is so cool.
