[Crash Course Kids Theme Song]
Have you ever noticed maybe on a nice
summer evening and you're running around
outside but your shadow looks super long,
but then at other times of the day it's
really short.
What's up with that?  Does your shadow have a mind of it's own like Peter Pan's?
Nope. I mean I hope not that'd be strange.
To understand how shadows move over the days.
Let's talk about what a shadow is,
exactly. Say you're standing outside in
the sun and you spot your body shadow.
Your body is solid that means it can
block sunlight since unlike can't pass
through your body it makes a dark area
behind it,
opposite from the direction the sun is
coming from. This dark part where the
sunlight can't reach is your shadow. So,
why doesn't this dark patch stay in the
same spot throughout the day?  Well for
one thing you move so your shadow moves with you.
But let's pretend you stand in
the same spot all day long.
No wait, that sounds super boring. Just
picture something that doesn't move
around, like a tree or a building. Its
shadow would still move throughout the day.
That's because the shadow is made by the
light of the Sun and the Sun is
constantly moving in the sky.
Well, you know, it's not really the Sun
that's moving. You should definitely
check out our video about how the earth
moves ,or rotates, on its axis making the
sun appear to move across the sky.
Even though it constantly seems to be
changing where it is in the sky,
some people know exactly where the Sun
is going to be at certain points during the day.
In fact ancient civilizations
thousands of years ago use the Sun like
a giant clock.
They could tell what time it was based
on the sun's position in the sky.
How they figure that out? Because the
sun follows a certain pattern every day,
these civilizations saw the Sun rising
in the east and setting in the West day
after day. Soon they were able to guess
what time it was based on where the Sun
was on its path from east to west.
Cool huh, and since the movement of the
Sun follows patterns during the day, so
does the movement of shadows
Any idea what the shadow patterns might
look like? Let's find out.
We'll follow the Sun for a day and see
how it changes the shadow of a specific
object. Then we can track the length in
the direction of the shadow from morning
to evening to see which patterns we can
spot. First let's pick an object that
stands still, not running around all
crazy. Like how about a lamppost, say one
that's about 4 meters tall. Now let's
start early in the morning, 7am
Sun show us what you got. The lamp post has a
pretty long shadow this early in the
morning and it looks like it's extending
to the west.
What happens to the shadow if we
fast-forward to 9am? Interesting,
the shadow still pretty long but not
quite as long as at 7am, and it's still
stretching out towards the west.
So let's see what happens at 11am. Well,
look at that .The shadows even shorter,
but again still pointing Westward, o in
the morning it looks like the lamppost
shadow starts out long and get shorter
as we get closer to noon, but they all
extend to the west. What happens at noon:
hardly any shadow.
The Sun is high in the sky at noon,
almost directly overhead.
Depending on where on earth an object is
it shadow will usually point north or south
at noon.
Rather than east or west let's see what
happens to the shadow in the afternoon.
Jumping to 2pm looks like the shadows are
getting a little bit longer again.
Now that the sun's going lower in the sky,
but unlike in the morning the shadow is
now pointing East.
Well the shadow continue to get longer
at 4pm. Yep it's definitely getting longer.
Still pointing East. To how about 6pm the
shadows about as long as it was in the
morning. Right?
But, again unlike in the morning the
shadow is stretching out towards the
east. So what patterns did we see the
lamppost shadow follow?
Let's look at these two bar graphs that
recorded our observations. In the first
graph we've charted the length of the
lamppost shadows.
Based on what we observed with the
lamppost the Sun created long shadows in
the morning when it was rising in the
east. When it was almost directly
overhead at noon the shadows were
shorter. Then as the Sun set in the West
in the afternoon the shadows got longer
again.
And what did we observe about the
direction the shadows were going in at
certain points of the day?
Well, like the second graph shows us, we
saw that the shadows in the morning and
afternoon face two different directions.
In the midday shadow was somewhere in
between. So, graph number one shows us
that when the Sun is low in the sky,
shadows are long. When it's high in the
sky, shadows are short. Graph number two
shows us that whatever direction the sun
is in the sky,
the shadows it creates will be in the
opposite direction.
So now you know what a shadow is and
that it changes in both length and
direction during the day depending on
where the Sun is in the sky.
Basically, the Sun is your shadows boss.
Yes Sun no Sun whatever you say Sun.
[them music]
