Transcript for Why is the sky blue?

– First of all, the sky isn’t just one color.

When professor Richard Zare gazes up at the sky,

he sees the colors that most of us know from the rainbow.

– You know, white light is really a combination of the colors of the spectrum:

red, orange, yellow, green, blue, purple.

And in his lab at Stanford, Zare’s students use advanced lasers...

...to learn how those segments of light behave.

Basically, different colors travel in different wavelengths.

The waves are wider on the red side of the spectrum and narrower at the violet end.

In the case of sunlight, it’s all very orderly...

... until the dfferent light waves collide with Earth’s atmosphere...

...and scatter across the sky at different rates.

– It turns out that violet light really is scattered much more than red light...

...and that’s why people say “Ah, that’s the reason the sky is blue!”

But professor Zare tells us that answer is way too simple. Here’s the problem:

If violet light is scattered the most, then it should be the most visible.

Why then, isn’t the sky purple?

– The light from the sun isn’t all of the same intensity in each color.

The sun actually peaks in the green/yellow region, like our eye does,

and falls off when you go towards the violet.

And less intensity on the violet side, shifts the tint back just slightly,

leaving the sky its familiar blue.