SriKumar wrote:Amber G....Any responses to 'why moutains look blue' question posed above?
Hi, there is already some discussion and explanation(s). Sorry if I am repeating some points or putting well known facts. Will just emphasize a few points in details, to clarify. Hope this helps. (Sorry for a long post
There are two main points here, first physics of light and second - physics of eye vision,
First physics of light:
Higher energy photon (higher frequency waves – or shortwave lengths) scatters more than lower energy photon, or longer wavelengths. Check out Rayleigh Scattering in Wiki, Very roughly speaking this scattering is proportion to 4th power of frequency. Roughly Blue/violet end of the spectrum (400 nm) scatters about 9.4 times more than red part (700 nm) of the spectrum. IOW all other things being equal, two laser rights of the same intensity far away , blue light will have about 10x less photons.
This is a quite rough analysis, other scattering like Mie or Raman does play quite a bit part too. But this is good enough for basic calculations.
At sunrise or sunset, when sun’s light passes through longer layer of atmosphere, most of the blue light is scattered away and you see a red (or redder) sun.
Meanwhile the “scattered photons” make the sky looks blue – these scattered photons are coming from all directions (not from the original source).
For Mountains - closer ones, naturally you can see more details, including colors – so one can see green trees, colored flowers etc..
Far away mountains (or anything else for that matter – even nothing) has blue tinge due to those scattered blue light (coming from sun and other sources). Basically one is *not* seeing any color details from the mountain ( even redder color present on the mountain is not that bright), everything you see is blue haze due to those scattered photons which makes the sky blue.
(If the far away mountain had a light house with a bright red LED light one can see it from far away – much farther than one can see a blue light but if there are not bright objects – which produces photons you see very little details)
(Roughly speaking, it’s not the mountains which turned into blue color – the blue haze is all over and one see dim mountain in that haze).
Physics of the Eye vision:
This aspect we do not teach much in ordinary physics class.
Basically with music our ear can detect full range of frequencies and we “hear” music very similar to what a wave analyzer will measure.
For light/color perception: we really do not see “frequency” of “color” of light as physicist define.
One suspects this, for example, orange color is “between” red and yellow (frequency wise) and when one mixes yellow and red one get orange. Not the same for purple color which eye sees as “mixture of red and blue”.
Basically, as Frank Wilczek once explained we are “tone-deaf”… our eye can just detect a very narrow band in three different frequencies and the whole color sense is quite complicated. (Even a cheap spectrometer is much better in detecting actual “color” (or frequency) of light than our naked eye). What color we see is, sometimes, quite different than one would “guess” from the frequency spectrum.
But that’s a different story. BTW, our own CV Raman did a lot of work in later part of his life, to help our understanding of physiology of eye and color vision.
(Long ago I enjoyed reading "Longing for the Harmonies" by Frank Wilczek who in my opinion is a very good explainer - Highly recommend the book as, IIRC, it nicely cover the chapter on physics of eye vision ).