Around one in every 10 Americans say that they believe that the earth is flat
or that they at least have their doubts that it's round. I'm going to test that.
I'm going to test if the earth is flat or not, and to do that I actually need to
go somewhere where it's super flat. So, that's why I'm going to Regina,
Saskatchewan, in Canada, and I'm going to measure and calculate the size of the
earth using just my bicycle and two sticks. This is not a joke. I'm here with
Casey at the Saskatchewan Science Centre and we've got two identical Sundials
set up right now since they're in the same place the shadows are the same
length. But I'm gonna be leaving one of them here with you Casey - you ready? okay!
He is going to set it up on this very spot right here, and I'm taking the
other sundial, and I've strapped it to my bike and I'm going to bike down that
road right there. That road is the reason that I've come all of the way to
Saskatchewan, because that road is perfectly straight for somewhere around
140 kilometers and I've come to measure that distance on my bike. Okay so I just
zeroed the odometer. Let's get started. Here goes science! Okay. This is highway
33 and since it's very flat here and there are no mountains to go around or
hills to go over, this is one of the longest straight roads in the whole
world and that's why I'm her. Let's pretend that this orange is the Earth.
now this is earth and these two sticks are gonna be
the two sundials we're working with. So I'm gonna put them in. Don't try this at home please!
Okay, since the orange is round any time we
line up the shadows like this they will never be the same length. If the shadow
on the right is short we can expect the one on the left to be longer. If they
were the same length than the orange would have to be flat. Now we can also
measure the length of the two shadows at the same time and measure the distance
between them and figure out the circumference. Since the Sun is really
far away we can treat its light as coming in parallel lines and therefore
we can figure out what angle it's hitting both of the sticks at. And that
allows us to figure out what angle the two sticks would meet up at in the
center of the orange without having to pull the orange apart. Let's say
that this angle here is 45 degrees. That's 1/8 of a circle, so the distance
between the two sticks - this distance here - that is 1/8
of the circumference around the orange. So we measure that distance
we multiply it by 8 and we know how big the orange - or the earth - is. That's what
I'm doing except instead of these two sticks we're using sundials and instead
of measuring this with a ruler I'm measuring it with my bike right now in
Saskatchewan. I've got the wind in my back and it is a beautiful day. I'm clocking
at 28.8 kilometers an hour. This is just great! Things are awesome! To celebrate
the 100 kilometer mark I'm going to eat the earth.
It's pretty good. It shouldn't surprise you that I'm not the first person to do
this experiment. a Greek scientist named Eratosthenes did it 2200 years ago
except instead of it being in Regina and Stanton he used the city's Alexandria
and Syene, and those cities were 800 kilometers
apart. He didn't have bicycles back then so he had someone pace the distance
between the two cities which is crazy - I mean they were 800
kilometers apart! And his measurements and his calculations were so precise that it
was still within 1% to 16% of the actual circumference of the earth. That's
incredible. But we don't know exactly what his answer was
because he used a unit called 'stadia' which was how big a stadium was, and
there were different sizes of stadiums and we don't know what one he meant, so
his answer has been lost to the sands of time. But, I'm gonna try to redo it with a
huge upgrade in technology we're using a bike. I biked a hundred and thirty-eight
kilometers today from Regina to reach the first stop sign it's the end of the
road and it is Stoughton. Ok so I just set up one sundial in Stoughton and
Casey set up the other one in Regina we made sure that they were both level and
checked that they were both aligned with one another and everything seems to be
good okay. I think my math was a tiny tiny bit off because I thought that the
measurement was going to take place at 10:59 and it is 11:04 and we're still a
few minutes away so I think it will be more like 11:15 but you know with this
experiment what matters is that the Sun dials are lined up with the road and
lined up with each other and I just got off the phone with Casey and Regina and
we are at the exact same point, the exact same angle right now, with our sundials.
At least this angle is the same. (yeah I know a little nerve-racking right?) We're
really close though! Mine is officially on the
meter stick. Is yours almost there? Okay so in, well in another like maybe.. we'll
say ten seconds you can grab your chalk. your line looks pretty good right?!
So this is it okay okay we'll take the measurements in three two one now I've
got okay I just measured my shadow and mine was 66.1cm,
and then I called Casey and his with 70.0cm
which means that our shadows are 3.9cm
different! Mine is 3.9cm smaller than his is in
Regina, which means that the earth is a sphere! And it means that I can calculate
the size of the Earth. Now I expect that it won't be exactly accurate but it's
going to be pretty darn close. Oh that's really really rad! Okay, cool... I'm gonna
hang up, and get packed, and get on the road. We now have all of the measurements
that we need in order to do the calculations for the circumference of
the earth. So I left Regina on my bike and I cycled all the way to Stoughton.
that distance was 138km when I got to Stoughton.
I set up a sundial that was 100 centimeters high and I measured the
shadow of the sundial at a specific time. The shadow was 66.1cm long
and so we can do some simple math to figure out the angle at
which the Sun was hitting the top of the sundial and that turns out to be 56.5°.
Now at the exact same time I was taking that measurement, Casey
in Regina was taking another measurement on an identical sundial.
his measurement was 3.9cm longer - he measured a shadow
of 70.0 cm and that means that the earth is a sphere and we
can calculate its circumference. We use the same math to figure out the angle
that the Sun hit the top of his sundial. That was 55.0°.
Since we know the angle that the Sun hit both of those sundials, and since the
Sun is really far away, we can calculate the angle that those two sundials would
meet up at if they met in the centre of the earth. We take the angle from Regina
and subtract it from the angle in Stoughton and we get 1.5°.
That means that the angle that those meet up at in the center of the
Earth is 1.5°, or 1/240th, of the circumference of the
earth. And now.. Now that we know that the distance we measured is1/240th of
the way around the whole earth, if we take the distance that I
measured (the distance that I biked) and multiply it by 240 we can figure out how
big the circumference of the entire world is. When we do that we end up with
33,120km. By my calculations
that is the size of the earth, and it's pretty darn close. The true size of the
earth is 40,075km which means that my
measurements and calculations are only 17% off. Eratosthenes'
measurements and calculations were, maybe, 16% off. I'm really happy with how that
turned out. When Eratosthenes did this experiment
over two thousand years ago he not only proved that the world is round but he
measured it and proved that it is a knowable thing.
The earth is something we can experiment on and learn about.
I'm really happy with how well my experiment turned out because I have
confirmed that the earth is indeed round and I measured it to be 33,120
kilometers around. And that's not exactly right,
but I mean my measurement is closer to the earth than it is to Mars and I'm
pretty happy with that. The reason my measurement isn't a hundred percent
accurate is because I didn't manage to line things up perfectly, so we took the
measurement about 12 minutes too late, which is enough to make an error of 17%
But still, I'm really, really happy with how well it turned out. I try
to do experiments that are almost impossible - that are just at the border
of being impossible [for me], and so if they always worked out perfectly 100 percent
of the time I think I wouldn't be trying things that are hard enough. Sometimes I
get asked 'how do I make enough money from these videos to fund big science
projects like this' and my answer to that is that I don't. I don't even make enough
money from this channel to pay for my expenses let alone my time, but if you
want - so that means someone just subscribed to my channel - if you want to
support what I do here on this channel please check out my patreon page every
little bit helps and actually every patron adds a drop in the bucket. Another
way you can support me is to subscribe to my channel and like this video. It's
not just meaningless Internet points it actually effects the algorithm which
changes how many people will see my science content. So, that's huge for me.
lastly I absolutely need to thank Casey and Ryan and everyone at the
Saskatchewan Science Centre for making this whole project possible. It just
wouldn't have been possible to measure the earth without them, so, please if
you're in Regina: check out this place! It is amazing. And, check out their website
I'll leave a link in the description below. Thank you so much for watching!