People have been looking at clouds since people have been… people. Those billowing shapes

might have been our first art or characters in our first stories. We still love to pick

out shapes, like bears, fish, flying saucers, faces, elephants. Some clouds even fly through

the sky like airplanes.

Which is weird because clouds are full of so much water that they can easily weigh as

much as a jumbo jet.

So why don't they fall out of the sky?

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There's lots of different kinds of clouds, but in the most general weathery terms, clouds

are big fluffy piles of water vapor that live overhead. As warm, humid air rises through

the lower atmosphere, it expands, cools, and some of it condenses into very tiny liquid

droplets. And so a cloud is born..

Just how that water vapor rises, though, depends on the type of cloud. If the wind pushes it

up a mountain like it's on a ski jump, we might get lenticular clouds. Humid jet engine

exhaust can make wispy cirrus clouds.

But maybe the easiest cloud to understand is everyone's favorite fluffball: cumulus.

They're also the easiest ones to draw.

So how do you keep the weight of a hundred elephants in the air? Buoyancy! Warm air is

less dense, so it rises, just like inside of a lava lamp.

Cumulus clouds appear over dark pavement, fires, sunny hillsides… any source of warm

updrafts. As the water vapor in that air is carried up, it cools, so its molecules slow

down, and some of them stick together, forming droplets that we can see.

We still have an unanswered question though: After the wind carries them away from the

warm updraft, why don't clouds fall back down?

Because of condensation! You know how when sweat evaporates off your forehead, you feel

cooler? That's because water moving from liquid to gas takes some heat with it. Condensation

is just the opposite. It releases heat.

So as the water in a cloud condenses, it heats itself from the inside, staying aloft like

a hot air balloon.

Da Vinci called them “bodies without surface”, which is why we can't live on them. But

maybe in them?

Lt. Col William Rankin did just that… accidentally anyway. As he was piloting his fighter jet

over the top of a massive cumulonimbus cloud, the engine caught on fire. He ejected and

fell from 47,000 feet straight into a 9 mile tower of lightning, thunder, ice, and rain,

carried up on 70 mph updrafts and barely conscious. He suffered from frostbite, bloodied from

the pressure change, bruised by hail, drowned by rain. What should have been a ten minute

parachute ride down to the ground instead took him 40 minutes.

He was definitely not on cloud nine. He was in it.

In the 1896 edition of the International Cloud Atlas, cumulonimbus, the world's tallest

and most powerful clouds, were placed at entry #9.

Unlucky pilots aren't the only living things inside clouds. Scientists found that living,

airborne bacteria make up as much as 20% of cloud condensation nuclei.

Not only are they home to airborne ecosystems, clouds are in some ways very much alive and

evolving themselves. Just take a few minutes and stare up at a fluffy cumulus, as its edges

billow and die. The rain that falls from them will one day rise again to become new clouds.

It's very “circle of life”.

LIVE TO GFX It might be because they're so alive that

their names sound like biological species. Cirrocumulus stratiformis! Cumulonimbus capillatus

incus!

Actually those sound like Harry Potter spells. Undulatus asperatus!

The greatest cloud photo of all time wasn't taken looking up at the clouds, but looking

down on them. When Apollo 17 astronauts brought this image back to Earth, it became the symbol

of a new environmental movement, demanding a new appreciation of our fragile planet.

29% of its surface covered by land, 71% covered in liquid water, but so many clouds. There's

a lot that scientists still don't know about clouds but they are definitely important and

they look cool. Like Gavin Pretor-Pinney says, they are nature's poetry writ large for

all to see.

What's a sunset without the clouds? It's just a disappearing circle. I mean, a plain

blue sky? Would be just… boring.

Clouds are what puts the “pale” in this “Pale Blue Dot”. I like that.

OUTRO LIVE

I've got some homework for you this week.

[BOOING NOISES]

Gavin Pretor-Pinney is the founder of the CIoud Appreciation Society and author of this

book, The Cloudspotter's Guide. This book will completely change the way you look at

the sky, I can't even sit by the window on planes anymore, because it's too overwhelming.

Gavin wrote about a trick that I'm challenging all of you to do: go outside and lie on your

back so you can look up and behind you at the clouds. They become the landscape, and

the ground becomes the sky. If you see anything cool, take a picture and

let me know here.

I only scratched the surface of the cloud world today, but there's a link to this

book down in the description, it might be the best book on clouds out there. I've

also included a link to the International Cloud Atlas, so you can learn to identify

all those puffy white things in the sky, and also a link to a video about Lt. Col William

Rankin, The Man Who Rode the Thunder.

Thanks for watching, and stay curious.

[MUSIC]

Oh man, look at all these clouds, there's a stratus cloud, there's a nimbus cloud, those

are great. And a Cumulonimbus, whoa watch out for that one. You guys are totally putting

me in the clouds right?