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Something about clouds

15 November 201408:00AMthings

Today in inappropriate use of Scitech's IT equipment: Blogging. For those keeping track at home, last week was coding.

There's something pretty cool going on here. And maybe it's a little bit obvious, and maybe this is one of those realisations that is only interesting to me, but I figured I'd share it anyway.

cloud panorama

This was taken at about half past six, and it looks like a pretty standard sunset, right? There's some nice contrast going on, maybe we could go down and take photos of it if that was our thing. We've got a couple of different types of clouds up there - some grey ones and some white ones - and the sun is setting behind them, right?

Well, no.

For starters, there's actually no such thing as a grey cloud. No, not even those big bad rainclouds. Dig through all the satellite photos you can find - or, more entertainingly, dig through a bunch of astronauts' Twitter feeds. Every cloud you see will be perfect, bleached-flour, tooth-whitening-agent white.

So, what's going on then? They sure look grey.

They, like many other grey things - are just white things that are really badly lit. A gigantic grey thundercloud only looks grey because there's no light hitting it when it's over your head - and also they have a tendency to be thicker.

What about these guys then? Why are they grey?

The thing that lights up clouds when they're in the sky - barring, like, lasers, is the sun, and obviously by about half past six the sun had dropped below the horizon.

Then how come there are still white clouds behind it?

Ah.Nnow that's the nifty part, and the part where my cloud geek gets to come out to play. Those clouds are textbook cirrus clouds, whereas the grey ones have a pretty typical fluffy cumulus shape. Cirrus are formed from falling ice crystals in the freezing upper atmosphere, whereas cumulus are basically the foamy condensing tops of thermal currents radiating from the warm, moist ground. Both created by warm air and cold air crashing into each other, but sort of from opposite directions.

But the white ones aren't white just because they're made of ice - I mean, a fluffy cumulus and a streaky cirrus are roughly the same colour at midday, right? They're white becausethe white(-y-yellow) ones are still lit because much like a man in a scissor lift can demonstrate, the sun sets at different times at different altitudes. And cirrus clouds are much, much higher.

cloud diagram

So for those clouds - despite being in exactly the same timezone - sunset hasn't happened yet! Up there in the very top of the troposphere, today is still happening.

And if we had enough types of clouds in enough different layers, we could watch the sun set in each one, one after the other, over and over until we ran out of atmosphere.

This is both a neat reminder that we're living on the surface of a sphere, and a neat bit of proof that clouds like to live at different altitudes. And if I can get a bit philosophical, it's also a reminder that mystery and wonder are not necessarily as strongly correlated as we like to think. What's cooler - thinking this is just different coloured clouds, like a thunderstorm, or looking up and seeing the clouds basking in same sunset you just watched just a few short minutes ago?

I mean, One of those is definitely cooler. I know which one I'd choose.

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