- Ah the seasons.
It gets cold in the winter,
flowers bloom in the spring,
we gets lots of sun in the summer,
and leaves fall in the fall.
See, the earth's seasons affect
every living thing on earth.
That's right, seasons affect the way
everything grows and changes, every year.
The reason we have seasons on earth,
is because the earth is tilted.
Now, let's say that this is the earth,
and there's an imaginary line
going through the middle of it
called the earth's axis.
It's tilted, and it stays tilted
as the earth goes around the sun.
At 100,000 kilometers an hour,
that's a billion kilometers every year.
Now, not only is the earth
going around the sun,
but the earth is spinning.
And, when you're on the part of the earth
that's towards the sun, it's daytime,
and when you're on the part of the earth
that's away from the sun, it's nighttime.
Now, the seasons work
in kinda the same way.
When the part of the earth that you're on
is tilted toward the sun,
it's summertime there.
So, when it's summertime
here at Nye Laboratories,
on the other side of the
world, it's wintertime,
in places like South
America and Australia.
- [Man] Hey Bill, your shoe's untied.
- Oh, thanks.
Then, when the part of
the earth that we're on
is tilted away from the
sun, it's wintertime here,
and it's summertime on the
other side of the world.
Isn't that wild?
All because the earth's axis is tilted.
That's the reason for the seasons.
Why are the North and South poles
the coldest places on the earth?
Well, please consider the following.
Let's say that this heat
lamp is like the sun.
Well, 'cause it's hot.
And, let's say that this
globe is like the earth,
'cause it looks like the earth.
Anyway, we've mounted thermometers
on the earth, like this, see?
Now, the one at the equator
is just about off the scale,
and the one at the South Pole
is right around the room temperature mark,
and the ones in between
are somewhere in between.
That's because the heat
is hitting the one at the
equator almost straight on,
whereas at the poles, it's
just barely grazing by,
and then somewhere in between,
well, it's somewhere in between.
You see, it's not that the
equator is closer to the heat,
it's that the heat is
hitting it more straight on.
See, if the earth was sitting like this,
then this thermometer
would be the hottest,
and this one would be the coldest.
Anyway, that's why the very
warmest places on the earth
are right around the equator,
tropical rainforests and jungles,
and the very coldest
places are at the poles,
because they're the ones that the energy
from the heat lamp just barely grazes by.
I mean, the energy from the
sun, I mean, well, anyway.
Thank you for joining me.
- [Narrator] Do you notice though,
that the axis about which the earth turns
is not straight up and down,
it's tilted to one side
at an angle of 23.5 degrees
from the perpendicular.
This has a lot to do with why
we have different seasons,
as we shall see.
- Let's say that this
plastic globe of science
is like the earth,
and we have two solar
panels mounted on it.
Now, solar panels convert light
directly into electricity.
So, right now, these two panels
are making enough electricity
to run these two little motors.
Right now, both motors are
going about the same speed.
Now, notice that we have one panel
in the northern half of the
earth, the northern hemisphere,
and one panel on the
southern half of the earth,
the southern hemisphere.
They're both receiving about
the same amount of light.
But, let's say it's summer
here at Nye Laboratories,
in the northern half of the
earth, the northern hemisphere.
That means that the earth would
be tipped towards the sun,
about like this.
Now look, the motor on
the southern hemisphere
is just barely moving,
and the motor in the northern hemisphere
is spinning like crazy.
Now, let's say it's six months later,
and the earth has gone around the sun
so that its axis is tipped this way.
Now look, it's reversed.
The one in the south is going wild,
and the one in the north
has slowed way down.
See, what that means is,
that this panel in the southern hemisphere
is receiving more light,
more energy from the sun
than the one in the northern hemisphere.
It's just like the earth's seasons,
right here, with the solar
panel plastic globe of science.
- [Narrator] Using a flashlight,
you can see for yourself
that direct rays are concentrated
on a smaller area than slanted rays.
This is why direct rays produce more heat.
