I know why the sky is blue during the day, and why it turns yellowish to reddish at sunrise and sunset. My question is; why doesn't the sky ever look green? Why does the color go from blue to yellow?
Asked by: Rulon Larsen
When the sky looks blue, it is due to the weak
scattering of blue light by and within the atmosphere,
due to an effect called Rayleigh scattering.
Effectively, air is slightly reflective of blue light.
When the sky (or clouds) look red, it is because
most of the blue light has been reflected away along
that line of sight, again due to Rayleigh scattering,
leaving the red light to arrive relatively unobstructed
to your eye from brightly lit white objects (eg clouds).
To a lesser degree than the red, but more so than the
blue, green light will also arrive along the line of
sight from bright objects. When green and red arrive
together, the human eye registers it as yellow. If
you doubt this, you need only examine a color tv screen
up close in a yellow area to see that it is actually
composed of tiny interleaved dots of green and red.
Similarly, to a lesser degree than the blue, but more
so than the red, green light will also be scattered
by the atmosphere. When blue and green light arrive
together, the human eye registers it as turquoise.
Again, look at a tv screen up close.
At points in the sky in between the red and blue colors,
some green light will be present, but the points will
appear either yellow or turquoise, depending on whether
there is more red or more blue light mixing with it.
When the blue and red are equal, the green will still be
less than either, since green scattering is weaker than
blue and green transmission is weaker than red. At these
points, the sky could look pink or lavender.Thus you
can never find a spot in the sky which looks purely green.
Answered by: John McGinn
The setting sun can actually produce a 'green
flash' for a short period of time, but it's very rare. Your best chances of seeing this are if your
very high up in the atmosphere (on a mountain for instance), it must be an extreamly clear day.
Look for it just after the sun sets below the horizion and you might see it.
The sky does not normally show us a green color due to several reasons. Wind, differences in
air temperatue and pressure, pollution, clouds all have a hand in it, but if your lucky, you might
catch a green sunset.
Answered by: Tony Mancuso
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