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Equality 7-2521 
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 Posted: June 16 2011 at 09:19 |
 Dean wrote:
Equality 7-2521 wrote:
Dean wrote:
Can we kill-off this yellow-sun/deep blue sky thing off once and for all?
Without cloud the sky is deep blue overhead and pale blue to white on the horizon because we are looking through more atmosphere when we look to the horizon:
If we look vertically up we are looking through 100km of atmosphere, when we look to the horizon we are looking through 1,133km of atmosphere (that's very simply geometry based on Pythagoras' theorem - anyone can work it out - I used an Earth radius of 6,378km), therefore the light is scattered 11 times more when we look to the horizon - this reduces the blueness of the sky and increases the yellowness of the sun.
A deep blue sky and a yellow sun is not possible on this planet circling this star- you either have a blue sky and a whitish sun or a whitish sky and a yellow sun. |
Just to be a little technical Dean the sun is slightly yellowish (slightly very key). This and the composition of our atmosphere (and probably our eyes a little bit too but I know much less about the human side) account for a deep blue rather than a violet from the scattering. The white hazy appearance of the sky directly above us is, in addition to what you have been saying, dependent on another type of scattering which is less predominate called Mie Scattering.
I also believe that the light would be scattered 121 times more towards the horizon because I think the Rayleigh equation is inversely proportional to the square of the radius. I don't have any physics textbooks near me to check that. Which is actually a big problem because there's a physics test today and I don't know where the center's textbooks disappeared to 
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Of course. There is a limit to how much technical detail I'm prepared (willing) to go into here firstly because my knowledge is basic, and also because it is unnecessary. The colour temperature of the sun puts the peak in the yellow region, but since it radiates across the whole visible spectrum at such a high magnitude we cannot distinguish this tint with the naked eye. The inverse square relationship would seem logical to me. |
I figured as much. You seemed interested in this since you're devoting a lot of time to this thread so I thought I'd share the little bit I know with you if you wanted some more info.
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"One had to be a Newton to notice that the moon is falling, when everyone sees that it doesn't fall. "
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Dean
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Posted: June 16 2011 at 09:41 |
Equality 7-2521 wrote:
I figured as much. You seemed interested in this since you're devoting a lot of time to this thread so I thought I'd share the little bit I know with you if you wanted some more info.
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That is much appreciated. But yes, more time than it deserves I think.
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What?
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Dean
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Posted: June 16 2011 at 11:01 |
Padraic wrote:
The monostatic 3D RCS in the Rayleigh regime is proportional to the square of the wavelength and the sixth power of the radius of the scatterer.
Edit: whoops, inversely proportional to the 4th power of wavelength. Haven't read my scattering text in a while.
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... R is the distance to the particle doing the scattering, lambda is the wavelength of the light, theta is the scattering angle and d is the diameter of the particle.
Which is facinating stuff and more interesting than contrails considering we are seeing the effect of particles considerably smaller than the wavelength of blue light (~475nm) as seen from 1,100 km away (allbeit billions of particles at ever decresing values of R until the light finally hits our retina).
Edited by Dean - June 16 2011 at 11:40
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What?
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Equality 7-2521
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Posted: June 16 2011 at 11:09 |
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It's amazing how much our life is shaped by the quantum world.
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"One had to be a Newton to notice that the moon is falling, when everyone sees that it doesn't fall. "
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Padraic
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Posted: June 16 2011 at 11:29 |
Dean wrote:
Padraic wrote:
The monostatic 3D RCS in the Rayleigh regime is proportional to the square of the wavelength and the sixth power of the radius of the scatterer.
Edit: whoops, inversely proportional to the 4th power of wavelength. Haven't read my scattering text in a while.
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... R is the distance to the particle doing the scattering, lambda is the wavelength of the light, theta is the radius of scatter and d is the diameter of the particle.
Which is facinating stuff and more interesting than contrails considering we are seeing the effect of particles considerably smaller than the wavelength of blue light (~475nm) as seen from 1,100 km away (allbeit billions of particles at ever decresing values of R until the light finally hits our retina). |
theta is an angle, but otherwise edit: I thought you wrote "radius of the scatterer". My bad.
Edited by Padraic - June 16 2011 at 11:29
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Padraic
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Posted: June 16 2011 at 11:31 |
The classic graph demonstrating scattering regimes: 
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Equality 7-2521
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Joined: August 11 2005
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Posted: June 16 2011 at 11:32 |
Padraic wrote:
Dean wrote:
Padraic wrote:
The monostatic 3D RCS in the Rayleigh regime is proportional to the square of the wavelength and the sixth power of the radius of the scatterer.
Edit: whoops, inversely proportional to the 4th power of wavelength. Haven't read my scattering text in a while.
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... R is the distance to the particle doing the scattering, lambda is the wavelength of the light, theta is the radius of scatter and d is the diameter of the particle.
Which is facinating stuff and more interesting than contrails considering we are seeing the effect of particles considerably smaller than the wavelength of blue light (~475nm) as seen from 1,100 km away (allbeit billions of particles at ever decresing values of R until the light finally hits our retina). |
theta is an angle, but otherwise
edit: I thought you wrote "radius of the scatterer". My bad.
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You just got out engineered son.
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"One had to be a Newton to notice that the moon is falling, when everyone sees that it doesn't fall. "
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Padraic
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Joined: February 16 2006
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Points: 31169
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Posted: June 16 2011 at 11:33 |
Equality 7-2521 wrote:
Padraic wrote:
Dean wrote:
Padraic wrote:
The monostatic 3D RCS in the Rayleigh regime is proportional to the square of the wavelength and the sixth power of the radius of the scatterer.
Edit: whoops, inversely proportional to the 4th power of wavelength. Haven't read my scattering text in a while.
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... R is the distance to the particle doing the scattering, lambda is the wavelength of the light, theta is the radius of scatter and d is the diameter of the particle.
Which is facinating stuff and more interesting than contrails considering we are seeing the effect of particles considerably smaller than the wavelength of blue light (~475nm) as seen from 1,100 km away (allbeit billions of particles at ever decresing values of R until the light finally hits our retina). |
theta is an angle, but otherwise
edit: I thought you wrote "radius of the scatterer". My bad.
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You just got out engineered son.
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I'll hand in my degrees in as I leave.
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Dean
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Joined: May 13 2007
Location: Europe
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Posted: June 16 2011 at 11:34 |
^ oops - copied that down wrong, I can't even read wiki properly - "scattering angle". 
/edit: you can have my degree - it's practically worthless anyway.
Edited by Dean - June 16 2011 at 11:35
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What?
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Padraic
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Posted: June 16 2011 at 11:35 |
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Dean
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Posted: June 16 2011 at 11:40 |
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What?
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Equality 7-2521
Forum Senior Member
Joined: August 11 2005
Location: Philly
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Points: 15784
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Posted: June 16 2011 at 12:02 |
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This thread is now about optics and all ecological discussion will be considered off topic.
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"One had to be a Newton to notice that the moon is falling, when everyone sees that it doesn't fall. "
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Padraic
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Posted: June 16 2011 at 12:04 |
Equality 7-2521 wrote:
This thread is now about optics and all ecological discussion will be considered off topic.
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Yay for actual physics.
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Dean
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Posted: June 16 2011 at 12:04 |
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..unless it's light polution.
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The T
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Posted: June 16 2011 at 12:26 |
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I wonder if birds also ruin our skies...
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Mr ProgFreak
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Posted: June 16 2011 at 12:53 |
The T wrote:
I wonder if birds also ruin our skies... |
For all we know, without birds in the sky the sun might be purple. 
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The T
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Posted: June 16 2011 at 14:26 |
Mr ProgFreak wrote:
The T wrote:
I wonder if birds also ruin our skies... |
For all we know, without birds in the sky the sun might be purple. |
Damn! Suspend all bird traffic now!
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Dean
Special Collaborator
Retired Admin and Amateur Layabout
Joined: May 13 2007
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Posted: June 16 2011 at 14:38 |
Except ostriches, emus, rheas, penguins and kiwis
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What?
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Equality 7-2521
Forum Senior Member
Joined: August 11 2005
Location: Philly
Status: Offline
Points: 15784
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Posted: June 16 2011 at 14:41 |
Dean wrote:
Except ostriches, emus, rheas, penguins and kiwis |
How can we say that those birds wouldn't fly if the sky wasn't so filled with airplanes? We had best ban their flight to be safe.
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"One had to be a Newton to notice that the moon is falling, when everyone sees that it doesn't fall. "
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Dean
Special Collaborator
Retired Admin and Amateur Layabout
Joined: May 13 2007
Location: Europe
Status: Offline
Points: 37575
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Posted: June 16 2011 at 14:57 |
Equality 7-2521 wrote:
Dean wrote:
Except ostriches, emus, rheas, penguins and kiwis |
How can we say that those birds wouldn't fly if the sky wasn't so filled with airplanes? We had best ban their flight to be safe.
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Stop me if I'm wrong, but I think penguins need pretty high humidity to fly.
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