Science > Physics > Why doesn't the sky go green before it goes red ni the evening?
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Science > Physics |
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"" |
| Date: |
13 Jan 2006 04:41:57 AM |
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Why doesn't the sky go green before it goes red ni the evening? |
I have a question here for anyone who can answer it, it's been
annoying me since Tuesday.
Why is the sky blue
http://www.sciencemadesimple.com/sky_blue.html
What I do understand:
* Light of shorter wavelength (blue) scatters easier than light of
longer wavelength (red).
* The sky is blue during the day because the blue part of the white
light from the sun is scattered as it passes through the atmosphere, so
everywhere we look at the sky we see blue.
* The sky is red in the evening because the sun's light has to
travel through more of the atmosphere. The shorter wavelength blue and
green light is scattered completely before it gets to the observer and
only the longer wavelength red light is making it to his eyes.
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green. Why isn't there a time
where the blue light has scattered completely, and the green light has
scattered enough to make the sky green?
There has to be green light coming from the sun that can be split from
the blue light otherwise we wouldn't see the green line in rainbows.
If you can get an answer on this from anyone I'd appreciate it.
from me, daniel.
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| User: "Hexenmeister" |
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| Title: Re: Why doesn't the sky go green before it goes red ni the evening? |
15 Jan 2006 05:50:56 PM |
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<daniel@braindelay.com> wrote in message
news:1137148917.295052.81800@z14g2000cwz.googlegroups.com...
I have a question here for anyone who can answer it, it's been
annoying me since Tuesday.
Why is the sky blue
http://www.sciencemadesimple.com/sky_blue.html
What I do understand:
* Light of shorter wavelength (blue) scatters easier than light of
longer wavelength (red).
* The sky is blue during the day because the blue part of the white
light from the sun is scattered as it passes through the atmosphere, so
everywhere we look at the sky we see blue.
* The sky is red in the evening because the sun's light has to
travel through more of the atmosphere. The shorter wavelength blue and
green light is scattered completely before it gets to the observer and
only the longer wavelength red light is making it to his eyes.
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green. Why isn't there a time
where the blue light has scattered completely, and the green light has
scattered enough to make the sky green?
There has to be green light coming from the sun that can be split from
the blue light otherwise we wouldn't see the green line in rainbows.
There is, and its been photographed.
http://antwrp.gsfc.nasa.gov/apod/ap040321.html
--
Der alte Hexenmeister ist:
Sorcerer Androcles Dumbledore, Headmaster, hogwarts.physics
school for zauberlehrlings.
"One muggle's magic is another sorcerer's engineering"
http://www.androcles01.pwp.blueyonder.co.uk/how_to_be_as_smart_as_einstein.htm
http://www.androcles01.pwp.blueyonder.co.uk/people_v_Baez.htm
http://www.androcles01.pwp.blueyonder.co.uk/sundials.htm
http://www.androcles01.pwp.blueyonder.co.uk/RR_C7/RelativityRevealed.htm
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| User: "Richard Henry" |
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| Title: Re: Why doesn't the sky go green before it goes red ni the evening? |
15 Jan 2006 05:55:28 PM |
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"Hexenmeister" <vanquish@broom.Mickey> wrote in message
news:AdByf.12753$lL4.9587@fe1.news.blueyonder.co.uk...
<daniel@braindelay.com> wrote in message
news:1137148917.295052.81800@z14g2000cwz.googlegroups.com...
I have a question here for anyone who can answer it, it's been
annoying me since Tuesday.
Why is the sky blue
http://www.sciencemadesimple.com/sky_blue.html
What I do understand:
* Light of shorter wavelength (blue) scatters easier than light of
longer wavelength (red).
* The sky is blue during the day because the blue part of the white
light from the sun is scattered as it passes through the atmosphere, so
everywhere we look at the sky we see blue.
* The sky is red in the evening because the sun's light has to
travel through more of the atmosphere. The shorter wavelength blue and
green light is scattered completely before it gets to the observer and
only the longer wavelength red light is making it to his eyes.
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green. Why isn't there a time
where the blue light has scattered completely, and the green light has
scattered enough to make the sky green?
There has to be green light coming from the sun that can be split from
the blue light otherwise we wouldn't see the green line in rainbows.
There is, and its been photographed.
http://antwrp.gsfc.nasa.gov/apod/ap040321.html
Nice photo of the Green Flash - often seen by California surfers who spend
late afternoons looking to the west along the horizon because that is where
the waves are coming from.
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| User: "tadchem" |
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| Title: Re: Why doesn't the sky go green before it goes red ni the evening? |
17 Jan 2006 03:49:36 PM |
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wrote:
<snip>
* Light of shorter wavelength (blue) scatters easier than light of
longer wavelength (red).
Correct
* The sky is blue during the day because the blue part of the white
light from the sun is scattered as it passes through the atmosphere, so
everywhere we look at the sky we see blue.
Also correct
* The sky is red in the evening because the sun's light has to
travel through more of the atmosphere. The shorter wavelength blue and
green light is scattered completely before it gets to the observer and
only the longer wavelength red light is making it to his eyes.
The sky is never red - at least I have never seed the sky turn red -
only the *clouds*. That is because after the sunlight has passed
through many miles of air, the shorter wavelengths are less abundant in
the sunlight, having been scatrtered along the way. The light that
does penetrate miles and miles of the air is disproportionately redder.
We can see that when this light is reflected off a cloud or contrail
or something *in* the air.
If you look *between* the clouds at sunset you'll see that the _sky_ is
a noticeably darker shade of blue than at mid-day.
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green. Why isn't there a time
where the blue light has scattered completely, and the green light has
scattered enough to make the sky green?
There is a "green flash" (a prismatic effect on the direct sunlight
itself) as others have said. That is not the same thing as a green
*sky*.
There has to be green light coming from the sun that can be split from
the blue light otherwise we wouldn't see the green line in rainbows.
Ever see a rainbow just at sunset? It's almost all red, yellow, and
orange. The green is very faint and the blue is almost totally
imperceptible.
Tom Davidson
Richmond, VA
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| User: "Sam Wormley" |
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| Title: Re: Why doesn't the sky go green before it goes red ni the evening? |
13 Jan 2006 09:33:29 AM |
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wrote:
* Light of shorter wavelength (blue) scatters easier than light of
longer wavelength (red).
* The sky is blue during the day because the blue part of the white
light from the sun is scattered as it passes through the atmosphere, so
everywhere we look at the sky we see blue.
* The sky is red in the evening because the sun's light has to
travel through more of the atmosphere. The shorter wavelength blue and
green light is scattered completely before it gets to the observer and
only the longer wavelength red light is making it to his eyes.
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green. Why isn't there a time
where the blue light has scattered completely, and the green light has
scattered enough to make the sky green?
There has to be green light coming from the sun that can be split from
the blue light otherwise we wouldn't see the green line in rainbows.
Why is the sky blue?
http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
"When we look up at the sky, the red cones respond to the small
amount of scattered red light, but also less strongly to orange and
yellow wavelengths. The green cones respond to yellow and the more
strongly-scattered green and green-blue wavelengths. The blue
cones are stimulated by colours near blue wavelengths which are
very strongly scattered. If there were no indigo and violet in the
spectrum, the sky would appear blue with a slight green tinge.
However, the most strongly scattered indigo and violet wavelengths
stimulate the red cones slightly as well as the blue, which is why
these colours appear blue with an added red tinge. The net effect
is that the red and green cones are stimulated about equally by the
light from the sky, while the blue is stimulated more strongly.
This combination accounts for the pale sky blue colour. It may not
be a coincidence that our vision is adjusted to see the sky as a
pure hue. We have evolved to fit in with our environment; and the
ability to separate natural colours most clearly is probably a
survival advantage".
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| User: "Andy Resnick" |
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| Title: Re: Why doesn't the sky go green before it goes red ni the evening? |
13 Jan 2006 12:16:11 PM |
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wrote:
I have a question here for anyone who can answer it, it's been
annoying me since Tuesday.
Why is the sky blue
http://www.sciencemadesimple.com/sky_blue.html
What I do understand:
* Light of shorter wavelength (blue) scatters easier than light of
longer wavelength (red).
Correct: that is Rayleigh scattering, which predicts the amount of
scattering to be inversely proportional to the 4th power of wavelength.
* The sky is blue during the day because the blue part of the white
light from the sun is scattered as it passes through the atmosphere, so
everywhere we look at the sky we see blue.
Sort of. The blue component is scattered the most (shorter wavelength =
more scattering in Rayleigh scattering), so when we look *away* from the
sun, we see a blue sky.
* The sky is red in the evening because the sun's light has to
travel through more of the atmosphere. The shorter wavelength blue and
green light is scattered completely before it gets to the observer and
only the longer wavelength red light is making it to his eyes.
Again, sort of. The longer wavelength is scattered the least, so we see
red.
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green. Why isn't there a time
where the blue light has scattered completely, and the green light has
scattered enough to make the sky green?
Well, clearly the sky is not a single hue of blue (or red)- there are
considerable amounts of chromatic variation. Not to mention the effects
of water vapor, air density (a sunset whilst in an airplane is
particularly spectacular), and, if you live in New Jersey, the various
amounts of toxic chemicals spewing forth into the atmosphere.
There has to be green light coming from the sun that can be split from
the blue light otherwise we wouldn't see the green line in rainbows.
google "green flash"
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
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| User: "" |
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| Title: It does too. (was: Why doesn't the sky go green before it goes red...) |
17 Jan 2006 01:36:44 PM |
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wrote:
What I don't understand is why there isn't a time, in between day
time and evening, where the sky is green.
That's begging the question. Before you ask *that* question, you have
to first ask the question: *does* it go green?
Though not as widely-known, there is a brief momentary green flash.
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