Why Do Distant Mountains Appear Blue?

No matter what color(s) mountain ranges may be up close, when they're off in the distance, they appear blue. Learn how our eyes and the atmosphere trick us in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/mountains-appear-blue.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey, Brainstuff, learn
voel bomb here. You may have noticed that whatever color
a mountain range may be up close, a verdant green
with foliage perhaps, or rusty clay red or capped with
cold white snow. From a distance, they all tend to

(00:24):
look blue. Australia's Blue Mountains and the Blue Ridge Mountains
of the Eastern United States weren't named at random. After all.
The beer brand COR's Light even used this science fact
as a gimmick using cans printed with temperature sensitive ink.
The little mountain peak in their logo turned from white
to blue when the package hit what the brand purports

(00:45):
to be the appropriate drinking temperature, that is, right around
forty eight degrees fahrenheit or eight point eight degrees celsius
or colder. But why blue? Oh, why not pink or
yellow or verdant green? On a clear day, it can
be hard to tell where some far flung mountain peaks

(01:06):
and where the blue sky begins. The sky itself usually
appears blue during the day thanks to atmospheric distortion and
the limits of human eyesight. It's a phenomenon called Rayleigh scattering.
Our sun the magnificent star upon which we all depend,
gives off electromagnetic waves across the entire visible spectrum and

(01:30):
a bit beyond it too. A sunlight usually appears white
or eyes because it's a mix of all of the
colors of the visible rainbow. We're talking red, orange, yellow, green, blue, indigo,
and violet. But all of those colors of light have
their own distinct wavelengths. A red light has the longest

(01:50):
wavelength among them, a violet has the shortest. The colors
all have their own amount of energy too. A red
light is relatively sluggish, while milet light is relatively zippy.
A sunlight requires an average of eight minutes and twenty
seconds to reach the Earth. Things get interesting once it

(02:10):
hits our atmosphere, which is loaded with unimaginably small air molecules.
Even wavelengths of visible light, which are only about four
hundred to seven hundred nanometers wide, absolutely tower over the
tiny air molecules, which are less than a single nanometer each,
But the size and energy of each particular wavelength of

(02:33):
light matters. Zippier light with shorter wavelengths is more likely
to hit those air molecules and get scattered around by them,
bouncing like pingpong balls from one molecule to the next
until it eventually hits our eyes from any number of
possible directions, And wouldn't you know it. Blue light has
one of the shortest wavelengths in the entire visible light spectrum,

(02:56):
which means that blue colors scatter most in the atmosphere.
It is true that violet wavelengths are even shorter, but
the Sun releases less violet light than blue light to
begin with, and human eyes detect blue more easily. This
scattering of so much blue light in the atmosphere, combined
with unequal blue light output from the Sun and the

(03:19):
biases of our own vision, answers that age old question
why is the sky blue? And we have this same
process to thank for the bluish tint of distant mountains.
When you gaze at a faraway summit, there's a whole
lot of atmosphere sitting between your eyeballs and the actual mountain.

(03:40):
The quantity will only increase with distance. A more air
means more air molecules, which means more light scattering. As
the space between you and your favorite mountain widens, the
mountain appears bluer and fainter until finally it disappears from sight.
That's why when we look at mountains far off in

(04:02):
the distance, they appear blue. However, other things in the
atmosphere can affect the way that we interpret a mountain's color.
A dust and pollution can cause yellowish hazes, and compounds
released by the vegetation adorning the aforementioned Blue Ridge Mountains,
which extend from Georgia, Pennsylvania, help produce that iconic bluish haze.

(04:29):
Today's episode is based on the article why distant mountains
appear blue to the Naked eye on how stuffworks dot Com,
written by Mark Mancini. Brain Stuff is production of iHeartRadio
in partnership with HowStuffWorks dot Com and is produced by
Tyler Klang. Four more podcasts from my heart Radio, visit
the iHeartRadio app, Apple Podcasts, or wherever you listen to
your favorite shows.