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Welcome to the bedtime sciences.
Tonight we're going all the way 

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up into space to learn about the
International Space Station. 

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Now here's my dad. 
Thanks, Blake, and welcome to 

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the Bedtime Scientist, everyone.
Tonight we're going to visit a 

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house above the earth. 
Not a pretend house, a real 1. 

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And right now, while you're 
getting ready for sleep, there 

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are people inside it, floating, 
brushing their teeth while 

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upside down, pulling themselves 
through narrow hallways with 

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just two fingers against the 
wall. 

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And outside the window, the 
entire planet is turning beneath

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them. 
Blue oceans, white clouds, dark 

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land freckled with light. 
Tonight, somewhere above you, 

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morning is arriving again. 
The house is called the 

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International Space Station, and
it's very, very high above the 

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Earth. 
If you stacked 20 Mount Everest 

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on top of each other, the 
station would still be higher, 

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about 250 miles above the 
ground, where the sky fades from

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blue into black. 
The station circles our planet 

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again and again, not once a day,
but every 90 minutes. 

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That means by the time you fall 
asleep tonight, the station will

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already be on the other side of 
the world. 

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It travels over oceans. 
It travels over deserts. 

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It travels over long stretches 
of dark water where moonlight 

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touches the waves, silver, 
white. 

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And inside the International 
Space Station, people drift 

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through the air as if they're 
underwater. 

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Except there's no water and no 
up and no down. 

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A sleeping bag might be attached
to the wall or the floor, or 

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beside a window in space. 
Those are all the same thing. 

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A pen can float beside someone's
shoulder for hours. 

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A small ball of water can drift 
across the room like a tiny 

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planet on Earth. 
Gravity pulls every drop of 

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liquid down into the shape of 
whatever holds it. 

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But up there, nothing pulls. 
So the water does what every 

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liquid wants to do. 
When nothing is pushing it 

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around, it rounds itself. 
Every drop of water, every tear 

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in space, becomes a tiny sphere,
a little ball held together by 

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something called surface 
tension, the same invisible pole

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that lets a droplet beat up on a
leaf. 

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Everything aboard the station 
has to be clipped down, zipped 

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shut or attached with Velcro, 
otherwise it floats away. 

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A sock drifts into the corner. 
A packet of food wanders through

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the air. 
Once, astronauts lost a spoon 

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for months before finally 
spotting it floating behind a 

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machine. 
Even though the space station is

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moving faster than almost 
anything humans have ever built 

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inside it, it can feel 
completely calm. 

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That's because the station is 
falling around the Earth. 

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Imagine throwing a ball as hard 
as you can. 

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It falls back down. 
Now imagine throwing it so much 

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faster that the earth begins to 
curve away beneath it. 

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The ball still falls, but the 
ground keeps bending out from 

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under it. 
So instead of landing, the ball 

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keeps going around the earth. 
That's what the station is 

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doing. 
It's falling all the time, but 

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the Earth keeps curving out of 
the way at exactly the same 

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speed. 
The station moves 5 miles every 

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second, fast enough to cross the
United States in about 10 

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minutes. 
The people inside the station 

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aren't just floating around for 
fun, They're working every day. 

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They study things that can only 
be studied in space. 

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They study how fire behaves when
there's no up on Earth. 

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A flame stretches upward like a 
teardrop. 

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Because hot air rises in space 
with no up to rise toward, a 

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flame becomes a tiny blue 
sphere. 

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It burns more slowly, more 
evenly, and it teaches 

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scientists how fuel really 
works. 

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They also study the human body. 
Bones grow lighter when nothing 

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pulls down on them. 
Muscles relax when they no 

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longer have to hold a body up. 
Our hearts pump differently 

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because it no longer fights 
gravity. 

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Every astronaut who lives up 
there teaches Dr. something new 

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about what a body needs to stay 
strong. 

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They also study botany to learn 
how plants grow when their roots

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can't tell which way is down. 
They study weather from above 

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the weather, and they study the 
stars without an atmosphere 

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blurring the view. 
All of this work is happening 

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tonight, right now, above all of
us. 

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The space station wasn't built 
by 1 country. 

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Pieces of it were made all 
around the world. 

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Hallways from America, rooms 
from Russia, laboratories from 

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Japan, Germany and Italy, a long
robotic arm from Canada, 

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research partners from Australia
and from many other places 

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beyond. 
The people who built those 

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pieces spoke different 
languages, wrote in different 

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alphabets, and grew up hearing 
different songs. 

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When they were small and one by 
one, over many years, humans 

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carried those pieces into space 
on rockets and connected them 

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together above the earth. 
A hallway that was built in one 

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country had to fit perfectly 
into a room built somewhere 

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else. 
A wire made by one team had to 

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connect to a machine designed by
another team across the world. 

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And somehow, they did it. 
Human beings who don't always 

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agree about things down here on 
Earth built a floating home 

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together in the dark. 
For more than 25 years now, 

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someone has always been living 
aboard the station. 

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Every single night since the 
year 2000, at least one human 

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being has been awake above the 
Earth. 

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No matter what was happening 
down below, no matter how loud 

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or quiet the day had been 
somewhere overhead, people 

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floated through the night 
together. 

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And because the station circles 
Earth every 90 minutes, the 

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astronauts see something that is
almost impossible. 

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They see 16 sunrises every day. 
That's 16 mornings. 

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The darkness outside the window 
begins to glow blue, then gold. 

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Then suddenly sunlight pours 
across oceans and clouds beneath

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them, the whole earth shining at
once. 

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Then 45 minutes later, night 
comes back again. 

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And then another sunrise. 
And another 16 times. 

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If they treated every sunrise as
a new morning, the day would 

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never end. 
So the astronauts made a 

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decision. 
Together. 

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They chose a bedtime. 
They picked 1 shared clock for 

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everyone aboard, no matter where
they came from, no matter which 

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language they dreamed in. 
At a certain hour, the lights 

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dim to amber, tablets go dark, 
voices become low. 

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Someone zips into a sleeping bag
attached to the wall. 

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Someone else takes one last look
through a round window at the 

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earth below. 
The oceans beneath them look 

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like a swirling blue puddle. 
Lightning flickers inside 

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faraway clouds. 
City lights spread across 

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continents. 
Then the window shade closes, 

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even while another sunrise is 
already beginning outside. 

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We built a tiny village in 
space, a place with no up or 

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down, and even surrounded by 
endless mornings, the people 

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there still understood something
important. 

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Living things need rest. 
Even explorers need sleep. 

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Even in space, night matters. 
And just before you drift off to

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dream of sleeping bags on walls,
lit windows above the earth, and

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the slow blue turning of the 
world, I want you to know 

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something about you. 
Your mind is a wonderful thing, 

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so full of curiosity, and I like
your mind just the way it 

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wonders. 
I'll be back again soon to 

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wonder more with you.