Ask A Scientist General Science Archive

Author:     library
Text:       Why is the sky blue?

Response #:  1 of 1
Author:      Mark Fernau
Text:        Something called "Raleigh scattering".  Wavelengths of sunlight 
that stimulate our eyes to see blue are reaching our eyeballs.  Air molecules 
are even smaller than the wavelength of light and so they scatter (reflect in 
all directions) the rays of light that come from the sun.  The air (oxygen and 
nitrogen) molecules scatter the shorter wavelengths of light (violet, blue, 
and green) much more effectively than the longer, redder wavelengths.  So our 
eyes are bombarded from all directions by scattered blue light.  Dust scatters 
all light equally so if the sky is real dusty it will look milky white.  I saw 
this once during a wind storm and it was really excellent looking!!  Also that 
is why the sky looks bluer in clean places like mountains.  Sunsets are 
reddish because the light has to pass through more sky than during the day so 
the bluer wavelengths are "scattered away" from our eye and the redder 
wavelengths move on a more direct path to our eyes.