(phone ringing)
- Hi, it's Doug.
It's winter time here in California
and it just never gets that cold.
But I have with me here
a chunk of dry ice.
Now this stuff is cold.
The reason I have to wear gloves
is because this is so
cold if I were touch it,
I would instantly get frostbite.
Someone named Valeria has
a question about the cold.
Let's give her a call now.
(phone ringing)
- Hi, Doug.
- Hi, Valeria.
- I have a question for you.
What's the coldest place on Earth?
- That's a great question.
Before I say anything more,
think about the coldest weather
you've ever experienced.
What was it like?
Now would be a good time to
pause the video and discuss.
Okay, you ready?
Well, for me personally,
I grew up near Chicago,
where I experienced some
pretty cold winters.
But that was nothing
compared to what my niece
and nephew experience.
They live in Yellowknife, a
town in far northern Canada.
And in winter, temperatures
there get as cold
as minus 40 degrees.
It's hard to even
imagine what that's like,
so let me give you a sense of it.
Here's a video of me when I visited there.
The snow is so deep that if
you run and jump into it,
you sink way down.
Even more amazing?
Watch what happens as someone tosses a cup
of hot water into the air.
Whoa, do you see that?
Some of it instantly turns to snow.
When I visited, I even got
to ride on a huge slide
made of ice, located
inside of a snow castle.
In places this cold,
you can even drive a car
on a frozen lake.
Because the ice is that thick.
Still, northern Canada isn't
the coldest place on Earth.
So, what is then?
Is it on top of the tallest mountain?
Maybe the North Pole?
Don't forget about the South Pole, too.
Which is it?
Well, the real question
is, how do we know?
How do scientists figure this out?
We could visit lots of these places,
and just try to decide
based on how it feels to us.
But once things get really cold,
it all just kinda seems the same.
We need some way to
measure how cold it is,
and that's where the thermometer comes in.
These days, we have digital
thermometers that tell us
the temperature outside,
like on this phone.
Or like ones you see on signs.
But since you can't see inside
one of these digital thermometers,
it's hard to understand
how a thermometer works.
It's easier if we have a look
at an old-school thermometer,
one like this.
A few hundred years ago,
someone noticed that if you take a thin,
hollow glass tube and you
fill it partway with liquid,
then suck all the air out
of the top of the tube,
the liquid will actually
rise up or down in the tube,
depending on how warm or
cold you get the tube.
If the tube gets warmed
up, the liquid rises.
If the tube gets cooled
down, the liquid goes down.
A few different people
had the brilliant idea
to add numbers along the side of the tube,
so that we could have a way to measure
how warm or cold something is.
These numbers are what we mean
when we talk about degrees.
Most of the world uses a temperature scale
invented by a scientist
named Anders Celsius.
The Celsius scale uses the
freezing point of water
as its zero degree
mark, so in other words,
when it starts to get cold
enough that liquid water
becomes solid ice, that's
zero degrees Celsius.
Anything colder than that is a minus,
or negative temperature like minus 40.
By comparison, the warmer the weather is,
the more the temperature goes above zero.
On the Celsius scale, the 100 degree mark
is the temperature at
which water starts to boil.
So basically, the temperature
of water on a stove.
Before the thermometer was invented,
no one really knew where the
coldest place on earth was.
But once it was invented,
scientists and explorers
could start taking
measurements of temperatures
all over the world, and
now, we know exactly
where the coldest place in the world is.
It's probably not going to surprise you
that both the North and the
South Pole are very cold.
But, what might surprise you
is that it's actually colder
at the South Pole than
it is at the North Pole.
In wintertime, the North
Pole is usually around
minus 35 degrees Celsius,
but the South Pole?
Temperatures in winter are
often around minus 60 degrees,
and the record all-time lowest
temperature ever recorded
reached almost minus 90 degrees Celsius.
That's four times colder than it even gets
inside your freezer!
It's not obvious why the South Pole
would be colder than the North Pole,
until you consider that
the North Pole is located
on basically on a low, frozen
section of the Arctic Ocean.
Whereas the South Pole is
on top of a giant ice sheet
more than a mile thick.
So the South Pole is
at a higher elevation.
And high elevation
places like mountaintops
are always colder than low places.
So in summary, the South Pole
is the coldest place on Earth.
We know this thanks to thermometers
that have been placed there
by explorers and scientists.
That's all for this week's question.
Thanks, Valeria, for asking it.
Now, for the next, now
for the next episode,
I reached into my question jar,
and chose three questions submitted to me
that I'm thinking about answering.
When this video's done playing,
you'll get to vote on one.
You can choose from,
why is December the
last month of the year?
Where do bugs go in winter?
Or, how are postage stamps made?
So submit your vote when the video's over.
I wanna hear from all of you watching.
There are mysteries all around us.
We're going to take a one-week break,
so stay curious and see you next time.
