Hank: So I've always assumed that skywriting is like, water vapor in the sky. It's clouds, right? No! It's canola oil!

Now, the water vapor trails that we usually see planes form come from the plane's combustion. This happens when oxygen and fuel react, creating carbon dioxide and water vapor. But the vapor isn't visible by itself; the water particles need to hit very cold air to condense into those tiny droplets that form the contrails.

The thing is, though, that happens way too high up in the sky for people to easily read a written message from the ground. So skywriting planes need to fly lower, where - unfortunately - it's not as cold. So they use a different strategy: smoke.

Skywriting planes carry canisters of mineral or canola oil, then the pilot flicks a switch to release the oil into the plane's exhaust, and the heat boils it. So when that vaporized oil is released into the less-cold air, it condenses into visible smoke clouds.

If you want a more environmentally-friendly option, though, you could just like, maybe talk to each other? Instead of writing in the sky? I don't know, that's just an idea.

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