World’s Most Asked Questions: Why is the Sky Blue?

It’s the mother of all questions! Well, except maybe What’s the Meaning of
Life? — which we actually have our own scientific answers to … Or What Is Love? — We have some thoughts
on that, too. But one of the most googled questions in the
English-speaking world is the one that kids are famous for asking — and grown-ups are
notorious for avoiding, because they just don’t know. Why is the sky blue? Just give me a couple minutes and I’ll let
you know why. This is the World’s Most Asked Questions! [Intro] The sky is blue because of three things: light
from the sun, particles in our atmosphere, and the fact that you’re a human. I’ll get to that last part in just a minute. But let’s start with how sunlight interacts
with particles in the sky. I’m not talking about dust or water droplets
or other big particles, which are sometimes mistakenly used to explain the sky’s blueness.
Instead, it’s the very small particles in our atmosphere that make the sky look blue. I’m talking about molecules of the air itself,
mostly molecular oxygen and nitrogen — O2 and N2. These molecules are super-abundant in our
atmosphere and so small that they’re even smaller than wavelengths of visible light! And that’s the key. Visible light consists of a range — or spectrum
— of different wavelengths. Light with the longest wavelengths are at the red end of
the spectrum, and light with the shortest wavelengths are at the blue and violet end. Since the blue wavelengths of light are shorter,
they’re more likely to strike those tiny molecules of oxygen and nitrogen more often,
and when they do, they get scattered in all directions. This effect is known as Rayleigh scattering,
because it was first described by John William Strutt, aka the Third Baron Rayleigh, who
in 1871 published his mathematical proof that blue wavelengths of light in the atmosphere
are scattered 16 times more than red wavelengths. But violet light has the shortest wavelength
of all visible light, and it’s scattered even more strongly by tiny particles — so
why isn’t the sky purple? Well, this is where being human comes into
play. Our human eyes perceive the middle of the
spectrum most sharply which is why blue is way easier to see than violet. So even though
violet light is being scattered around like crazy, we just don’t detect it as well as
we detect the blue. And that’s why the violet band of the rainbow is often the hardest for
us to make out. So SciShow viewers are in luck, because when
we surveyed you, the most popular favorite color from the rainbow was blue. 33.55% of
survey takers reported blue as their favorite color, while yellow was the least favorite
at only 2.8%. Poor yellow. But, there are other animals that can see
all the way into the ultraviolet end of the spectrum, like honeybees and some birds. So
maybe they like yellow. And maybe the sky looks completely different to them. Of all the fascinating questions in the world,
what question do you want answered most? Let us know on Facebook or Twitter or in the comments
down below, and we will try to answer those questions in a new video at the end of the
month. And don’t forget to use hashtag #WMAQ and stay tuned for more answers to the World’s
Most Asked Questions.