Posted by Phillip Noll on August 17, 2007 at 10:12 AM
As I was looking at various photos of sunrises and sunsets the other day I got to thinking of all the magnificent colors we see in the sky at these times. Deep and/or pastel pinks, purples, reds, oranges, golds, yellows, and blues and just about every possible combination of these colors depending upon conditions. Seems like every color of the rainbow can be represented in the sky during sunrise/sunset with one exception. Where's the green? Roy G Biv without the "G".
Why is it that green is absent from our skys when nearly every other color is present? Why is that particular narrow range of wavelengths not represented when all others appear to be? Even when you see bright yellow clouds against a blue sky there is still no hint of green--not even on the edges of the clouds. None, nada, zip.
The only time I have seen green in the sky is during very dangerous and intense storms that are spawning tornadoes. Its almost as if you are underwater--very scary.
Perhaps the answer is obvious and I'm just missing it sitting here in my early morning "fog". Anyway, thought it would be a fun question to ask.
Phillip, I am thinking way back to my first lesson in color. All of the colors you do see are hues of the primary colors. Green is not a primary color - "yellow and blue make green" still echos in my brain from nearly 60 years ago. I think (emphasis on 'think') that is your answer.
I'll be curious to see the other answers you may get to this one.
Good question Phillip. I remember from my physics classes of yore that there's an explanation, but darned if I can dredge it up from my mind's immaculate filing system.
I'll add to your list of exceptions when you do see green. With fires on the mainland and sometimes with dust storms stirred up in nearby Katmai NP, we do get a green cast that can be really tricky to dial out of skies.
Sometimes we also get the proverbial green flash at sunset and especially at sunrise. Not what you were asking about, but it's as green as Dorothy's emerald city.
Posted by Mel Ladewig on August 17, 2007 at 11:37 AM
Light from the sun is a distribution of various wavelengths including wavelengths outside the visible range of humans. There is no "primary" color in that sense with regards to sunlight.
I've seen colors I'd describe as green in sunsets in my part of the world from time to time. There is also a famous phenomenon in coastal areas know as the green flash.
I don't know why green isn't more prominent in our sunrises and sunsets. It is a large component of the inbound light and is supposedly the color to which huma eyes are most sensitve. My guess is that there are fewer atmospheric particles that scatter or reflect the green light or that there are more which scatter it outward at the first contact with the atmosphere reducing the green component in the light that reaches us as the sun sets.
Mel-
Posted by Richard Wong on August 17, 2007 at 2:33 PM
the northern lights.
Posted by Alex Lofquist on August 17, 2007 at 8:23 PM
Green is considered a primary color along with red and blue. The secondary colors are yellow, cyan (blue-green) and magenta. Magenta is one of the few colors that is not in the optical spectrum, being an admixture of red and blue. It is important to not confuse physiological colors with physical colors. The human eye only sees primary colors but interprets their hue depending on their brightness.The green isn't missing from the sky, it is just misplaced. If you wish to see it, just hold a sheet of paper in front of you in the mid afternoon. It will look white. Viewing it through a green filter will block the shorter and longer wavelengths and let the green show through. It was always there! A prism or diffraction grating can give a more dramatic display of the sunlight passing through our atmosphere.
Strictly speaking, there are some wavelengths (colors) of light that are blocked, but these are quite narrow and can only be seen with a good spectroscope or spectrograph.
Posted by Doyle Thomas on August 19, 2007 at 12:57 PM
Check this out:
http://mintaka.sdsu.edu/GF/
Doyle
Posted by Doyle Thomas on August 19, 2007 at 12:58 PM
Mel has it right. What you're seeing is not a prismatic effect that will have a full "rainbow" but rather light waves coming in from different sources. Around the sun it will be in the 600-700nm range (yellow/red) and in the sky above it will be in the 400-450nm range (violet/blue). There is nothing there to generate light in the green range (~550nm)
Discussion
8 repliesWhy is it that green is absent from our skys when nearly every other color is present? Why is that particular narrow range of wavelengths not represented when all others appear to be? Even when you see bright yellow clouds against a blue sky there is still no hint of green--not even on the edges of the clouds. None, nada, zip.
The only time I have seen green in the sky is during very dangerous and intense storms that are spawning tornadoes. Its almost as if you are underwater--very scary.
Perhaps the answer is obvious and I'm just missing it sitting here in my early morning "fog".
I'll be curious to see the other answers you may get to this one.
I'll add to your list of exceptions when you do see green. With fires on the mainland and sometimes with dust storms stirred up in nearby Katmai NP, we do get a green cast that can be really tricky to dial out of skies.
Sometimes we also get the proverbial green flash at sunset and especially at sunrise. Not what you were asking about, but it's as green as Dorothy's emerald city.
I've seen colors I'd describe as green in sunsets in my part of the world from time to time. There is also a famous phenomenon in coastal areas know as the green flash.
I don't know why green isn't more prominent in our sunrises and sunsets. It is a large component of the inbound light and is supposedly the color to which huma eyes are most sensitve. My guess is that there are fewer atmospheric particles that scatter or reflect the green light or that there are more which scatter it outward at the first contact with the atmosphere reducing the green component in the light that reaches us as the sun sets.
Mel-
Strictly speaking, there are some wavelengths (colors) of light that are blocked, but these are quite narrow and can only be seen with a good spectroscope or spectrograph.
http://mintaka.sdsu.edu/GF/
Doyle
http://mintaka.sdsu.edu/GF/
Doyle
Guy