Hi, BTN.
It's me, Evie, and I'm wondering, why is the world round?
Also, big fan. Love you, guys.
JACK: (IN ROBOTIC VOICE) Somewhere, a long time ago,
like, more than 4.5 billion years,
a committee was meeting to decide the shape of our planet.
Oh, I don't know. I still think a cube is the right shape.
What about a pyramid?
Then we can hide treasures inside it.
For the last time, we're not going with a pyramid,
but once we've decided on the shape of Earth,
you can put as many pyramids on it as you like.
I can't wait. I love pyramids. They're straight to the point.
(LAUGHS)
It could always be flat.
How about a sphere?
A sphere?
Yeah. A round sphere.
Huh. I like it!
And that, my dear BTN viewers,
is not the reason why the Earth is round.
Yeah, 'cause it's flat.
Shh!
The real reason why the Earth is round
is a lot less science fiction
and a lot more science faction, or scientific.
It's all to do with gravity.
You know, that force that attracts everything to everything else.
The force of Earth's gravity pulls equally from all sides,
which is why people on the other side of the planet
don't fall off.
All of us and all the stuff the Earth is made of
are being pulled towards the centre of the planet
with equal force, which gives you a sphere shape.
The same thing is happening
to all the other planets in our solar system,
which is why they're also round.
Well, kinda.
Technically, the Earth and other planets are more of an...
..irregularly shaped ellipsoid. What?
I think Earth should be an irregularly shaped ellipsoid,
you know, not exactly a sphere,
but close enough so everyone thinks it is.
You see, when objects like planets spin and spin and spin,
things on the outer edge have to move faster
than things on the inside to keep up
and that causes a sort of bulge along the equator.
Now, today, we know the Earth is round
because of, well, duh, technology
and, like, we've been to space,
so we can see it and go, "Yeah, it's round,"
but before that, many thought it was...
Flat.
I still think it makes sense for it to be flat.
Oh, sure, sure, sure, sure.
And what happens when you reach the edge?
Do you just fall off?
I don't know. Something...magical?
Yeah, that was pretty much what most people thought for a long time,
but not this guy, Pythagoras,
who you might know as the guy
who invented PIE...thagoras's Theorem.
Anyway, in the 6th century BC,
he reasoned that if the moon was round,
then the Earth must be too.
OK, so not exactly a scientific breakthrough,
but a pretty good theory.
A couple of hundred years later,
this guy, Aristotle, also declared that the Earth was round,
but this time he backed it up with observations he made
based on which constellations he could see in the sky
as he travelled further and further away from the equator.
And then, in 240 BC,
this guy, Eratosthenes, actually measured the Earth...
..not with a measuring tape -
instead, he did some calculations
based on the position of the sun at certain times and locations
and worked out that...
The Earth's circumference is 39,375 kilometres.
Ooh, so close.
It's actually 40,075 kilometres,
but, like, working that out without the tech we have today,
impressive.
Oh, thank you!
Still, the whole round Earth idea didn't really catch on
until people started to sail right around it and not fall off...
..which is probably the main reason why
I've decided the Earth will be...
A pyramid! ..round.
Round. We're going with round, OK, people?
Round.