why does the sky look bluer in autumn?
autumn scenery in inner mongolia province. (photo: vcg)
by staff reporters
to understand why the sky looks bluer in autumn, we need to first comprehend why it looks blue.
sunlight consists of multiple colors with different wavelengths. the red light has the longest wavelength, while purple and blue lights have the shortest wavelengths.
when sunlight passes through earth's atmosphere, it encounters a layer of tiny molecules and dust particles which cause the component lights to scatter. due to their short wavelengths, blue and violet lights scatter more than the others.
we see the blue light rather than purple because of the physiology of the human eye. our eyes are more sensitive to blue, so we see the sky as blue.
in autumn, the blue sky looks even bluer for several reasons.
it’s the time when the sun moves before the tropic of capricorn. therefore the sun's rays are no longer directly above us but at an angle to the sky, which increases the volume of scattered blue light visible at the ground level.
autumn not only lowers temperature but also humidity. with less water vapor in the air, it is harder for clouds to form, leaving the sky blue.
additionally, blue and orange are complementary colors. in autumn, leaves turn orange and red, providing a stark contrast to the blue sky, making it even bluer.
