From the brains behind brains on, this is the moment of um.

Answering those questions that make you go. Welcome to Moment of Um from APM Studios. I'm Molly Bloom. Put your shoes on, open your front door, and take a big, big breath.

Oh, fresh air. Feels good, right? Air is essential to everything we do. Breathing, walking,

running, living. If it's so important to our life force, then why the heck can't we see it?

Hi, I'm Kalia. And I'm Anya.

We're from Olin Park, Illinois, and our question is, why is air invisible?

Hi, I'm Vicki van dergerer.

I studied chemistry, and in my job, I try to ensure that the medicines you buy in a pharmacy are safe to use.

To understand this, first you need to remember that all the matter around you is made up of molecules.

Some of these are big complicated molecules or collections of molecules and some are really simple molecules.

In general, the big, complicated molecules can do a lot of different things when light hits them.

They can absorb the light or they can scatter in all directions, or even send the light straight back like a ping pong ball.

For example, the molecules and carrots are really good at sending back orange bits of light and absorbing the rest, which is why carrots appear orange.

So how about air?

Well, air is mostly made up of very simple nitrogen and oxygen molecules, which really can't do much with visible light.

They can't really absorb it, they can't really reflect

it, so the light generally passes straight through the air as if the molecules weren't even

there. It's the same with the pane of glass. The structures making up the pain of glass

don't interact much with visible light and let most of it pass through. And when light passes

straight through something, that means you can't see it.

So do the molecules in the air do nothing with light?

Well, not quite. They do scatter the light a little bit, especially the blue light,

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