A child on a grassy hill points up at a big blue sky with a bright golden sun and fluffy clouds.

Why is the sky blue?

Sunlight looks white. The air is clear — you see right through it. So where does all the blue come from? Let's find out.

First clue: sunlight only looks white. Tap it and see what's really inside.

tap the white light

Next clue: the air is full of tiny specks. When sunlight hits them, the blue bounces off every which way — but red zooms straight through.

A golden sunbeam hits a cluster of tiny air specks: blue light splatters off them in every direction while a red beam passes straight through and keeps going.

But why blue and not red? Blue light is a tiny, quick wiggle — small enough to catch on the specks and bounce off. Red is a big, slow wave that rolls right past them.

A small tight blue wave crashes into tiny specks and scatters in dotted arcs, while a big slow red wave below rolls straight past the same specks.

So all that scattered blue, coming at you from every direction — that's your blue sky!

But what if light crosses a LOT of air? Drag the slider and count how many chances the blue gets to bounce away.

air to cross: a little
thinthick

More air gives blue more chances to bounce away. The colour that gets out stays hidden — use the clues to predict it.

Look how far the light has to travel.

Two panels of the same child on a hill: a high noon sun sends a short beam straight down through a little air, while a low sun sends a long beam sideways through much more air to reach the same child.

At noon the light takes a short hop through the air. At sunset it has to cross a HUGE amount of air… 🤔

You just saw: thicker air steals the blue.

So when the sun drops low and its light crosses all that extra air — what colour does the sun turn?