YouTube: https://youtube.com/watch?v=1SN1BOpLZAs
Previous: Earth's Rotation & Revolution: Crash Course Kids 8.1
Next: Hunting for Properties: Crash Course Kids #9.1

Categories

Statistics

View count:506,772
Likes:1,561
Dislikes:155
Comments:268
Duration:04:53
Uploaded:2015-05-01
Last sync:2018-11-25 02:20
Have you ever wondered why your shadow is longer sometimes and shorter others? It turns out it all has to do with that marvelous big ball of light in the sky; The Sun!

This first series is based on 5th grade science. We're super excited and hope you enjoy Crash Course Kids!

///Standards Used in This Video///
5-ESS1-2. Represent data in graphical displays to reveal patterns of daily changes in length and direction of shadows, day and night, and the seasonal appearance of some stars in the night sky. [Clarification Statement: Examples of patterns could include the position and motion of Earth with respect to the sun and selected stars that are visible only in particular months.] [Assessment Boundary: Assessment does not include causes of seasons.]

Want to find Crash Course elsewhere on the internet?
Crash Course Main Channel: https://www.youtube.com/crashcourse
Facebook - https://www.facebook.com/YouTubeCrashCourse
Twitter - http://www.twitter.com/thecrashcourse
Tumblr - http://thecrashcourse.tumblr.com

Credits...

Executive Producers: John & Hank Green
Producer & Editor: Nicholas Jenkins
Cinematographer & Director: Michael Aranda
Host: Sabrina Cruz
Script Supervisor: Mickie Halpern
Writer: Kay Boatner
Consultant: Shelby Alinsky
Script Editor: Blake de Pastino

Thought Cafe Team:
Stephanie Bailis
Cody Brown
Suzanna Brusikiewicz
Jonathan Corbiere
Nick Counter
Kelsey Heinrichs
Jack Kenedy
Corey MacDonald
Tyler Sammy
Nikkie Stinchcombe
James Tuer
Adam Winnik
{Intro Music}

Have you ever noticed, maybe on a nice summer evening and you're running around outside, that 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 its own like Peter Pan's? Nope, I mean, I hope not. That would be strange. To understand how shadows move over time, let's talk about what a shadow is exactly.

Say you're standing outside in the sun and you spot your body's shadow. Your body is solid. That means it can block sunlight. Since sunlight 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. It's 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's going to be at certain points during the day. In fact, ancient civilizations thousands of years ago used the sun like a giant clock. They could tell what time it was based on the sun's position in the sky. How did 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 of what those 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 chart the length and 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 lamp post? Say one that's about four meters tall. Now let's start early in the morning. 7 AM. 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 9 AM? Interesting. The shadow's still pretty long but not quite as long as at 7 AM, and it's still stretching out towards the west. So let's see what happens at 11 AM. Well, look at that. The shadow's even shorter, but again still pointing westward. So, in the morning it looks like the lamp post shadow starts out long and gets 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, its 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 2 PM. Looks like the shadows are getting a little bit longer again now that the suns going lower in the sky, but unlike in the morning, the shadow is now pointing east. Will the shadow continue to get longer at 4 PM? Yep, it's definitely getting longer. Still pointing east, too. How about 6 PM? The shadow's 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 lamp post 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 lamp post shadows. Based on what we observed with the lamp post, 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 faced two different directions, and 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 point 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 shadow's boss. "Yes, sun." "No, sun." "Whatever you say, sun."


{Outro Music}