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Old 06-05-2008, 03:06 PM #17
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Default Re: Why is the sky blue? (Answer)

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Originally Posted by Switch
Meh, "the sky is blue because oxygen is blue" : That's no answer.....why is oxygen blue? :P
I tend to agree.


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Old 06-05-2008, 03:35 PM #18
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Default Re: Why is the sky blue? (Answer)

Yeah, well, the answer is above...Rayleigh scattering.Probably happens in water too.
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Old 06-05-2008, 03:45 PM #19
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Default Re: Why is the sky blue? (Answer)

If the sky is blue because oxygen is blue then why aren't the stars and moon blue? Why are sunsets orange? I think Rayleigh scattering fits better.
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Old 06-05-2008, 03:56 PM #20
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Default Re: Why is the sky blue? (Answer)

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Originally Posted by cmendoza
If the sky is blue because oxygen is blue then why aren't the stars and moon blue? Why are sunsets orange? I think Rayleigh scattering fits better.
By that logic, why isn't the sun blue? It's because the magnitude of the light coming through is so great as to mitigate the effect. The moon doesn't appear blue because it is bright enough that the amount of red and green absorbed is negligible. It's a lot like water, in that if you shine a light, it does get a slight tint to it, but only after an enormous distance does water actually absorb enough other wavelengths to make the light appear blue.

The sky is blue because air in the atmosphere diffuses sunlight, and the oxygen reflects the blue. The sky turns orange at sunset because ice crystals act as prisms, and diffract the blue and green light upwards, into outer space, while orange/red goes straight.
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Old 06-05-2008, 03:56 PM #21
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Default Re: Why is the sky blue? (Answer)

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Originally Posted by cmendoza
If the sky is blue because oxygen is blue then why aren't *the stars and moon blue? *Why are sunsets orange? *I think Rayleigh scattering fits better.
Because oxygen scatters short wavelengths better (violet and blue light) and the rest pass through easier, with less scatter.That's the reason sunsets are orange/red too(which was also explained above).The sunlight has to pass through a way bigger volume of air and ozone so because O[sub]3[/sub] filters a huge amount of the UV and violet, and O[sub]2[/sub] scatters blue around, so red and yellow reach your eyes in higher proportions (and probably IR too).

Oxygen isn't really blue.Well, it is , but not for the same reason a pair of blue glasses are.The glasses filter long wavelengths and lets only blue pass, oxygen however doesn't filter long wavelengths it just let's them pass through , while blue get's scattered all over (including into the eye of the beholder).
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Old 06-05-2008, 03:58 PM #22
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Default Re: Why is the sky blue? (Answer)

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The moon doesn't appear blue because it is bright enough that the amount of red and green absorbed is negligible.
This is where I think you're wrong.Green and red do not get filtered, they just pass right through oxygen , while violet and blue get reflected and scattered off of the oxygen molecules, giving the impresion that the oxygen itself is blue.
Maybe that's the reason why sunlight is slightly yellowish and not white.
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Old 06-05-2008, 04:13 PM #23
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Default Re: Why is the sky blue? (Answer)

I think this argument is arising because of a fundamental misconception. :-[

Objects are not inherently one color or another, but rather they have the appearance of color because of the wavelengths of light that they absorb and reflect respectively; grass is green because it absorbs red light and blue light; hence the green light is reflected. Oxygen is"blue" because it reflects blue light more readily.

So when I say that oxygen is blue, it is because it reflects blue light. Oxygen being blue is then explained through Rayleigh scattering (essentially, an explanation to the explanation).

When I originally posted in this thread, I meant it as a simple explanation. The sky is blue because Oxygen is blue, and we see the blue because of Rayleigh scattering.

The sky turns orange at sunset because water droplets/ice crystals in the upper atmosphere act as prisms.
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Old 06-05-2008, 05:50 PM #24
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Default Re: Why is the sky blue? (Answer)

Interesting discussion.

Actually the sky does not look blue because of oxygen in the air. It looks blue because the amount of scattering is wavelength dependent. Blue scatters more then green or red, hence the sky looks blue. The shorter the wavelength, the more scattering will occur. I'm not sure if our atmosphere contains particles small enough to scatter UV, but if it does and we could see UV, the sky would look UV.

It's true that the color of an object is determined by the way the object absorbs and reflects wavelengths of visible light, but that has nothing to do with rayleigh scattering. If rayleigh scatting would be an explanation for the color of an object, that object would then lose its color in a deep vacuum. After all, rayleigh scatting needs particles < wavelength of light to occur.
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Old 06-05-2008, 06:07 PM #25
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Default Re: Why is the sky blue? (Answer)

Quote:
Originally Posted by Petrovski
Interesting discussion.
It's true that the color of an object is determined by the way the object absorbs and reflects wavelengths of visible light, but that has nothing to do with rayleigh scattering. If rayleigh scatting would be an explanation for the color of an object, that object would then lose its color in a deep vacuum. After all, rayleigh scatting needs particles < wavelength of light to occur.
Atoms are smaller than the wavelength of all visible light, as are molecules. Molecules make up all objects (that we know of).
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Old 06-05-2008, 06:14 PM #26
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Default Re: Why is the sky blue? (Answer)

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Objects are not inherently one color or another, but rather they have the appearance of color because of the wavelengths of light that they absorb and reflect respectively
That was what I tried to say before.


Quote:
The sky is blue because air in the atmosphere diffuses sunlight, and the oxygen reflects the blue. The sky turns orange at sunset because ice crystals act as prisms, and diffract the blue and green light upwards, into outer space, while orange/red goes straight.
But how can you be 100% sure of the orientation of the crystals? They don't have to be ALL facing upwards, so how can they reflect or let thru light on the same direction?
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Old 06-05-2008, 06:36 PM #27
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Default Re: Why is the sky blue? (Answer)

Quote:
Originally Posted by mikewitt
Atoms are smaller than the wavelength of all visible light, as are molecules. Molecules make up all objects (that we know of).
And what atoms or molecules do you expect to find in a deep vacuum, like for instance space?
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Old 06-05-2008, 06:41 PM #28
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Default Re: Why is the sky blue? (Answer)

Quote:
Originally Posted by Petrovski
And what atoms or molecules do you expect to find in a deep vacuum, like for instance space?
Dark matter

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Old 06-05-2008, 06:48 PM #29
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Default Re: Why is the sky blue? (Answer)

Quote:
Originally Posted by daguin
[quote author=Petrovski link=1212608788/24#26 date=1212691002]And what atoms or molecules do you expect to find in a deep vacuum, like for instance space?
Dark matter

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[/quote]

Explain, please, oh guru.
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Old 06-05-2008, 06:50 PM #30
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Default Re: Why is the sky blue? (Answer)

Quote:
Originally Posted by nikokapo
Quote:
Objects are not inherently one color or another, but rather they have the appearance of color because of the wavelengths of light that they absorb and reflect respectively
That was what I tried to say before.


Quote:
The sky is blue because air in the atmosphere diffuses sunlight, and the oxygen reflects the blue. The sky turns orange at sunset because ice crystals act as prisms, and diffract the blue and green light upwards, into outer space, while orange/red goes straight.
But how can you be 100% sure of the orientation of the crystals? They don't have to be ALL facing upwards, so how can they reflect or let thru light on the same direction?
They aren't triangular prisms, they're spherical. It's like a rainbow.

Quote:
Originally Posted by Petrovski
[quote author=mikewitt link=1212608788/24#24 date=1212689265]
Atoms are smaller than the wavelength of all visible light, as are molecules. Molecules make up all objects (that we know of).
And what atoms or molecules do you expect to find in a deep vacuum, like for instance space?
[/quote]
You asked how an object could have color in a vacuum. The object to which you are surely referring is composed of molecules.
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Old 06-05-2008, 06:54 PM #31
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Default Re: Why is the sky blue? (Answer)

Quote:
Originally Posted by nikokapo
[quote author=daguin link=1212608788/24#27 date=1212691264][quote author=Petrovski link=1212608788/24#26 date=1212691002]And what atoms or molecules do you expect to find in a deep vacuum, like for instance space?
Dark matter

Peace,
dave
[/quote]

Explain, please, oh guru.
[/quote]

http://en.wikipedia.org/wiki/Dark_matter

http://cosmicvariance.com/2008/02/27...e-dark-matter/

That should keep you busy for awhile.

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Old 06-05-2008, 07:03 PM #32
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Default Re: Why is the sky blue? (Answer)

"In astrophysics and cosmology, dark matter is a hypothetical form of matter that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter."

Good enough, I have to go finish a History essay
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