- #1
cragar
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how is the sky blue and not purple? how come purple light is not scattered , or how come the sky does not appear purple to us .
Why is the sky blue and not purple?
- Thread starter cragar
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In summary: Food for thought.The "blue" in blue sky is attributed to Rayleigh scattering of sunlight. The frequency (wavelength) dependence is f4 (lambda-4). Purple is an admixture of red and blue. There is very little "red" in "blue" sky. Have you noticed that at 90 degrees to the sun, the blue sky light is nearly completely polarized (only when the air is cloudless and really pollution free). Why polarized?The blue in blue sky is attributed to Rayleigh scattering of sunlight. The frequency (wavelength) dependence is f4 (lambda-4). Purple is an admixture of red and blue. There is very little "red" in "blue" sky. Polar
- #2
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Your eyes don't work as well on violet as they do on blue.
http://curious.astro.cornell.edu/question.php?number=688
http://www.msnbc.msn.com/id/8631798/
http://curious.astro.cornell.edu/question.php?number=688
http://www.msnbc.msn.com/id/8631798/
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- #3
cragar
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so violet light is scattered our eyes just don't pick it up.
- #4
uart
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cragar said:
The whole range of visible frequencies are scattered, from red through to violet. However with more scattering happening at the blue-violet end and less at the red-orange end our eyes perceive this mixture of colors as blue.
- #5
cragar
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i see
- #6
protonchain
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In fact birds see the sky in ultraviolet because their eyes have evolved that way.
Food for thought.
Food for thought.
- #7
Bob S
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The "blue" in blue sky is attributed to Rayleigh scattering of sunlight. The frequency (wavelength) dependence is f4 (lambda-4). Purple is an admixture of red and blue. There is very little "red" in "blue" sky. Have you noticed that at 90 degrees to the sun, the blue sky light is nearly completely polarized (only when the air is cloudless and really pollution free). Why polarized?
- #8
tiny-tim
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purple stripes
Hi cragar!
Only the stripes are purple …
cragar said:
Hi cragar!
Only the stripes are purple
…Nat King Cole said:
- #9
granpa
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blue is short wavelength light. red is long wavelength light. short wavelength light is scattered more.
purple isn't in the rainbow
purple isn't in the rainbow
- #10
uart
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I'm pretty sure that cragar actually meant violet even though he said purple, that was my interpretation of the question anyway. My understanding of what cragar was asking is basically : given that shorter wavelengths are the most readily scattered - and violet is the shortest wavelength we can see - then why don't we see the sky as violet.
Actually it's interesting that although technically violet (the spectral color at around 380-420nm) and purple (typically a mixture of blue and red) are very different, in terms of human perception they are indeed very similar. Violet is necesarily represented as a shade of purple in RBG color-space on a computer monitor and it isn't all that bad an approximation of what the spectral color actually looks like (in terms of human perception). So in my opinion cragars use of the term purple, in the context of "how should the sky appear to us", really wasn't at all inappropriate (even if he was really referring to violet).
Actually it's interesting that although technically violet (the spectral color at around 380-420nm) and purple (typically a mixture of blue and red) are very different, in terms of human perception they are indeed very similar. Violet is necesarily represented as a shade of purple in RBG color-space on a computer monitor and it isn't all that bad an approximation of what the spectral color actually looks like (in terms of human perception). So in my opinion cragars use of the term purple, in the context of "how should the sky appear to us", really wasn't at all inappropriate (even if he was really referring to violet).
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- #11
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Didn't you ever learn the mnemonic Roy G. Biv? The colors of the rainbow are Red, orange, yellow, Green, Blue, indigo, and violet. Isaac Newton thought the spectrum should have seven items to match the number of days in the year.granpa said:
Some rainbows:
That's exactly how I interpreted his question. The question to be answered isn't "why is the sky blue?" cragar apparently knows the stock answer to this question as talks about scattering in the original post. He is questioning this stock answer, and this stock answer is only partially correct.uart said:
The question to be answered is "If scattering is the sole answer to 'why is the sky blue', why isn't the sky indigo, or even violet? After all, indigo and violet should be scattered even more than is blue." The answer to this deeper question lies not only in the sky but also in our eyes and in the way in which we perceive color.
When there is a lot of scattering the sky can appear to be indigo, or even violet.
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- #12
cepheid
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Why is violet followed by even more green in both of the pictures of rainbows that D H posted?
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I posted three pictures of rainbows, not two. The first two are of supernumerary rainbows. For more, google that phrase, or see
http://www.atoptics.co.uk/rainbows/supers.htm
http://www.jal.cc.il.us/~mikolajsawicki/rainbows.htm
http://www.atoptics.co.uk/rainbows/supers.htm
http://www.jal.cc.il.us/~mikolajsawicki/rainbows.htm
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FAQ: Why is the sky blue and not purple?
Why is the sky blue and not purple?
The sky appears blue during the day because of a phenomenon called Rayleigh scattering. The Earth's atmosphere is made up of gases and particles, which scatter sunlight in all directions. Blue light has a shorter wavelength compared to other colors, making it scatter more easily and giving the sky its blue appearance.
Can the sky ever appear purple?
Yes, the sky can appear purple during certain times of the day, such as sunrise and sunset. This is because the angle of the sun's rays passing through the Earth's atmosphere becomes longer, causing more scattering of blue light and allowing red and purple light to be more visible.
Is the color of the sky the same all over the world?
No, the color of the sky can vary depending on factors such as location, weather conditions, and time of day. For example, in areas with high levels of air pollution, the sky may appear more gray or even brownish. Additionally, the color of the sky can also be affected by the amount of water vapor and dust particles in the atmosphere.
Why does the color of the sky change throughout the day?
The color of the sky changes throughout the day due to the position of the sun in the sky. As the sun rises and sets, the angle of the sun's rays passing through the Earth's atmosphere changes, causing different colors to be scattered and making the sky appear different shades of blue, pink, orange, and purple.
Can the color of the sky affect our mood?
There is some evidence that suggests that the color of the sky can affect our mood. Studies have shown that blue light can help improve focus and increase alertness, while purple light can have a calming effect. However, the overall impact of sky color on our mood may vary from person to person and can also be influenced by other factors such as personal experiences and cultural beliefs.