字幕列表 影片播放 列印英文字幕 [MUSIC] 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? [MUSIC] 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?