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? [music] ?

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KIDS: Our World!

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EVAN: Hey Globey, you’re
looking a little "two

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dimensional" today. Did you
know that a few hundred years

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ago, people actually thought
you were flat? After all, they

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could look out on the horizon
and things looked like they

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were flat for as far as humans
could see.

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Sailors even had the false
belief that if they kept

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sailing in a straight line,
they would eventually

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fall off the earth.

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Of course today we know you’re
not flat. You’re a sphere.

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Did you also know Globey that
people once thought you were

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the center of the solar system?

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That’s right. They thought the
Sun and the other planets in

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our solar system revolved
around earth. In fact, they

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thought everything in the
universe revolved around Earth.

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But in 1543, an astronomer
named Copernicus claimed the

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Sun was the center of our solar
system. But not many people

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thought he was right. They held
strong to their

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mistaken beliefs.

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Then another astronomer named
Galileo proved the Earth was

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not the center of our solar
system.

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He used his telescope to
observe that Venus had

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different phases...like our
Moon.

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For example, sometimes the Moon
is full in the sky and

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sometimes it’s just a sliver.

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This is caused by the Moon’s
orbit around our Earth as well

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as our planet’s orbit around
the Sun.

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We know the Moon does not make
its own light. It can only

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reflect light from the Sun.

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The Sun lights one half of the
Moon. The other half is always

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dark. During the Moon’s orbit

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around the Earth we see
different fractions of the

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lighted half so the Moon
appears to change shape.

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We call these changes phases of
the Moon.

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The time from one phase of the
Moon until the next time it

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reaches the same phase is 29.5
days

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Galileo correctly assumed since
Venus also displayed different

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phases like our moon, then that
must mean it was orbiting the

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Sun and not Earth.

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This was his hypothesis, and
today we know he was right.

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But at the time, many leaders
thought Galileo was outright

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crazy. In fact, they charged
him with a crime

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for his beliefs. And sentenced
him to house arrest for the

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remainder of his life. Can you
imagine that?

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Let’s talk about the word
"hypothesis" for a moment.

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A hypothesis is a statement
that can be tested using the

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scientific method.

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That basically means a
hypothesis is someone’s idea

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that hasn’t yet been proven
right or wrong.

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When scientists are using the
scientific method, they are

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making observations, asking
questions, and looking for

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possible explanations for what
they see.

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They form a hypothesis, then
test that hypothesis.

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And that’s one of the exciting
things about science.

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At its very basic level,
science is about the

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search for truth. Scientists
and astronomers develop ideas

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about the universe and then set
out to prove that what they

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believe is right. Sometimes
though, scientists prove the

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hypothesis is wrong, and that
forces them to revise and

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change their ideas. Even a
hypothesis that is right can

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lead to new questions and the
process begins all over again.

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CARLA BITTER: On Earth our
hypothesis change all the time.

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Less than a hundred years ago,
we had no idea that microbes

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caused disease. If you think of
the stories of yellow fever.

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It was the hot air. It was the
miasma.

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It was the bad air coming off
the river. And when it got

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cold, people wouldn’t be sick
anymore.

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The outbreak would end. But
nobody really knew that "oh,

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it’s a mosquito." It’s this
critter that’s carrying this

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microbe that is biting you,
getting in your bloodstream.

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This is what’s making people
sick. So, that’s an idea, the

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hypothesis of the miasma off
the river or the vapors coming

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out of vents or whatever where
the leading theories of what

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was causing yellow fever a
hundred years ago.

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We know now that simply, it’s a
microbe. And you can solve it.

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You can fix it. You can say,
let’s start developing a

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vaccine. Because we know what
this mechanism is now.

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Let’s eradicate mosquitos so
people don’t get bitten.

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So you can take precautions and
you can have solutions when you

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start turning over hypothesis
and coming up

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with an idea of how things
really work.

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EVAN: The planet Mars is
another example of where

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scientists have revised their
ideas. Many astronomers who had

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gazed at Mars through their
telescopes, believed the planet

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had liquid water because they
observed both dark and light

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patches on its surface. They
thought the dark patches were

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water and the light patches
were continents.

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But in 1965, NASA sent the
Mariner 4 to fly by the planet

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and take photographs. The
Mariner 4 captured the first

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pictures of another planet
taken from deep space.

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It was during this mission that
scientists realized there was

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no liquid water on the surface
of Mars. But had there

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ever been? Some scientists
believed there had been.

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Some did not.

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In 2008, NASA sent the Phoenix
Lander to Mars.

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During its mission, the robotic
arm of the Phoenix Lander dug

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just below the surface of Mars

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and discovered frozen water...
ice!

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The Phoenix Lander has also
discovered that the soil of

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Mars was different than they
originally thought.

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So Globey, these are just a few
examples of changing ideas.

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And with all we’ve learned
today, I’m going to make a

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hypothesis of my own. If new
discoveries are made in the

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next decade, scientists will
continue to revise and change

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their beliefs. It’s a very
exciting process. And one that

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helps us discover the truth
about our world

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and our universe.

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? [music] ?

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KIDS: Our World!

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