YouTube: https://youtube.com/watch?v=SeSexM-wVzA
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Duration:04:15
Uploaded:2018-01-11
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[ Intro ]Oh my gosh!

Squeaks and I were having such a wild game of catch that Squeaks’s watch flew off and smashed to smithereens! You know what they say… time flies when you’re having fun.[Squeaks is distressed…]So if your watch has broken down... how will you know when it’s time for lunch?

Not to worry, Squeaks! You can still figure out what time it is, by making a sundial![Squeaks is relieved.]A sundial is a device that uses the sun to tell time. It’s one of the oldest kinds of scientific instruments we have, and the earliest one used to measure time.

Most sundials these days use a flat base, and a stick called a gnomon. Whenever the sun is shining, the gnomon casts a shadow. And we can look at where the shadow falls to tell us what time it is!

Since ancient times, people have been making all kinds of sundials to help them tell time. And having a sundial in your house, or your school, or your library, lets everyone know that around here, people care about science![Squeaks squeaks]And also, it’s useful to have in case your watch stops. Want to make your own sundial?

As long as there’s sunlight outside, you can! Take something long and straight – like a stick, or even a drinking straw – and stick it into the ground. That’s your gnomon!

If you live in the northern hemisphere like Squeaks and me, your gnomon should be tilted on a little bit of an angle, towards the north. If you live in the southern hemisphere, it should point south. You may need a grown-up friend to help you figure out which way north or south is.

Squeaks and I figured it out together![Squeaks squeaks.]Every hour, go outside and look at the shadow your gnomon is making on the ground. Then, just make a mark where the shadow falls. You can start at 7 AM, do it again at eight o’clock, then nine o’clock… and keep going until the sun sets!

You may want to set an alarm every hour, so you don’t forget. To mark down the gnomon’s shadow, you can use a rock, sidewalk chalk, or really anything you want. You can get fancy and have your friend or grown-up help you draw lines out from the gnomon, like spokes on a wheel.

You can even add numbers! That way, tomorrow you can go back outside, look at the shadow, see what number or lineit’s falling on, and know exactly what time it is! At any hour of the day, the sun is lighting up half of the earth.

And the earth is constantly rotating, from west to east. So when we see the sun rising in the east, it means our part of the world is on the very edge of the sunlit side. And we cast a shadow behind us, to the west.

Same with the gnomon on your sundial! In the morning, the gnomon casts a shadow to the west. And as the earth rotates through the day, making the sun look like it’s moving across the sky, the shadow moves clockwise – the same direction as the hands on a clock! – around the sundial.

If you want to make a sundial but there’s no dirt around, you can try sticking a gnomon into a bucket filled with sand or pebbles. You can also use a paper plate! You might need you r grown-up to help you find the very middle of the plate, poke your stick or your straw through, and point your sundial towards the north or south, depending on what hemisphere you’re in.

As long as the plate is facing the same direction every time you take it outside, it’ll still work! And if you want to get really crazy, you can make…. a HUMAN SUNDIAL! Where the gnomon is you!

If you go outside and stand on the same spot every hour and have a friend mark where your shadow falls, you can go stand in the same spot again tomorrow, look at your shadow,and see what time it is![If we want to show Jessi and Squeaks doing this:]Squeaks and I took turns being the gnomon and doing the measuring. Just remember to never look directly at the sun. Even while you’re building a sundial!

You may want to measure your markings again every few months, to keep your sundial as accurate as possible. And your sundial won’t be quite as accurate as the ones that are made by scientists. Perfectly accurate sundials need to be aligned using a lot of math, depending on where you are in the world, and depending on the time of year!

But even though we’ll be getting Squeaks a new watch, and in the meantime we have plenty of other clocks, we’re still super psyched to go outside and use the sun to find out what time it is! Oh, look at the time! Our sundial says we have to go, but we’ll see you next time here at the Fort![OUTRo]