(This isn’t a thing I learned recently, it’s an answer to something cousin_it said he didn’t understand. Though I would not be surprised [1] if in fact he already understands all this and what he’s not-understanding is some deeper more detailed thing that I don’t understand either.)
[1] Merely on the general grounds that cousin_it strikes me as a clever person who knows many things.
The sky is blue for the same reason as the sun is yellow. The actual light from the sun is white (a better way to say this: our idea of what counts as white is derived from the spectrum of the sun), and as it passes through the atmosphere some of it gets scattered in other directions. So if you look at the sky but not directly at the sun, you are necessarily seeing scattered light; and if you look directly at the sun, you are seeing the sun’s light with the scattered light removed.
Shorter-wavelength light scatters more easily than longer-wavelength light. You can do the actual calculations and find exactly how much more easily—perhaps these details are what cousin_it is saying he doesn’t understand—but qualitatively it’s obvious enough: a photon gets scattered when it excites one of the atom’s electrons, which after a while returns to a lower-energy state and re-radiates, and higher-energy photons do that more readily.
When the sunlight’s path through the atmosphere to you is longer, at sunrise or sunset, more scattering happens, which is why the sun looks redder then. More of the shorter-wavelength light is going elsewhere.
That’s the best explanation of Rayleigh scattering I’ve ever seen, thank you!
I guess the interesting questions begin when you try to convert the explanation to a prediction, like “Mommy, was the sky always blue?” or “will it be blue in the future?” That requires knowing a lot more things then just Rayleigh scattering. My knowledge is just enough to tell me that I don’t have a clue. For example, even with just Rayleigh scattering (ignoring all other factors) the sky could also be violet (even shorter wavelength, right?) or orange (if the atmosphere was thicker and most blue light got scattered into space). Then you get into things like the spectrum of the Sun, the composition of the atmosphere, the way water washes out dust, the factors that prevent losing water to space, the role of the biosphere, etc. To answer these innocent questions it seems like you need to know literally all sciences!
As a matter of fact, the nitrogen makes sky blue, but the oxygen makes it green. Had been more oxygen than nitrogen in our atmosphere, they sky would have been green, all else equal.
You can also say, that this blue color is the color of 20000 K, on the Wein’s diagram. Which is the temperature (kinetic energy) of the nitrogen atom hit by an UV photon of the appropriate energy to be absorbed.
And our planet in fact loses water by the hydrogen escaping. 50 kilogram per second.
Well, this I think I know without Googling, You may refine this by—Googling it.
Is this actually true? Do you have a source? I have tried Googling for it.
My understanding is that the sky’s blue color was caused by Rayleigh scattering. This scattering is higher for shorter wavelengths. There’s no broad peak in scattering associated with nitrogen absorption lines (which I imagine would be very narrowband, rather than broadband).
Wikipedia’s article on Rayleigh scatting mentions oxygen twice but makes no reference to your theory.
That’s the best explanation of Rayleigh scattering I’ve seen, thank you!
The really fun questions begin when you try to convert explanation to prediction, like “was the sky always blue?” or “what color will it be in the future?” To answer these, you pretty much need to know all the sciences, from astrophysics to evolutionary history. My education is only enough to tell me that I don’t have a clue. Just look at other planets, they all have differently colored skies due to different factors, which could also affect Earth at other points in time.
That’s the best explanation of Rayleigh scattering I’ve seen in a while, thank you!
The interesting questions start at the next layer. For example, the same Rayleigh scattering could also lead to a violet or purple sky depending on the composition of sunlight. Or it could lead to an orange sky if the atmosphere was thicker and most of the blue got scattered into space. Or it could be all sorts of other colors due to atmospheric gases or dust. At long timescales, all these factors can change a lot. So if I try to convert the simple explanation into a prediction—“Daddy, was the sky always blue? What color will it be in a billion years?”—my mind goes everywhere at once.
(This isn’t a thing I learned recently, it’s an answer to something cousin_it said he didn’t understand. Though I would not be surprised [1] if in fact he already understands all this and what he’s not-understanding is some deeper more detailed thing that I don’t understand either.)
[1] Merely on the general grounds that cousin_it strikes me as a clever person who knows many things.
The sky is blue for the same reason as the sun is yellow. The actual light from the sun is white (a better way to say this: our idea of what counts as white is derived from the spectrum of the sun), and as it passes through the atmosphere some of it gets scattered in other directions. So if you look at the sky but not directly at the sun, you are necessarily seeing scattered light; and if you look directly at the sun, you are seeing the sun’s light with the scattered light removed.
Shorter-wavelength light scatters more easily than longer-wavelength light. You can do the actual calculations and find exactly how much more easily—perhaps these details are what cousin_it is saying he doesn’t understand—but qualitatively it’s obvious enough: a photon gets scattered when it excites one of the atom’s electrons, which after a while returns to a lower-energy state and re-radiates, and higher-energy photons do that more readily.
When the sunlight’s path through the atmosphere to you is longer, at sunrise or sunset, more scattering happens, which is why the sun looks redder then. More of the shorter-wavelength light is going elsewhere.
That’s the best explanation of Rayleigh scattering I’ve ever seen, thank you!
I guess the interesting questions begin when you try to convert the explanation to a prediction, like “Mommy, was the sky always blue?” or “will it be blue in the future?” That requires knowing a lot more things then just Rayleigh scattering. My knowledge is just enough to tell me that I don’t have a clue. For example, even with just Rayleigh scattering (ignoring all other factors) the sky could also be violet (even shorter wavelength, right?) or orange (if the atmosphere was thicker and most blue light got scattered into space). Then you get into things like the spectrum of the Sun, the composition of the atmosphere, the way water washes out dust, the factors that prevent losing water to space, the role of the biosphere, etc. To answer these innocent questions it seems like you need to know literally all sciences!
As a matter of fact, the nitrogen makes sky blue, but the oxygen makes it green. Had been more oxygen than nitrogen in our atmosphere, they sky would have been green, all else equal.
You can also say, that this blue color is the color of 20000 K, on the Wein’s diagram. Which is the temperature (kinetic energy) of the nitrogen atom hit by an UV photon of the appropriate energy to be absorbed.
And our planet in fact loses water by the hydrogen escaping. 50 kilogram per second.
Well, this I think I know without Googling, You may refine this by—Googling it.
Is this actually true? Do you have a source? I have tried Googling for it.
My understanding is that the sky’s blue color was caused by Rayleigh scattering. This scattering is higher for shorter wavelengths. There’s no broad peak in scattering associated with nitrogen absorption lines (which I imagine would be very narrowband, rather than broadband).
Wikipedia’s article on Rayleigh scatting mentions oxygen twice but makes no reference to your theory.
https://en.wikipedia.org/wiki/Rayleigh_scattering
That’s the best explanation of Rayleigh scattering I’ve seen, thank you!
The really fun questions begin when you try to convert explanation to prediction, like “was the sky always blue?” or “what color will it be in the future?” To answer these, you pretty much need to know all the sciences, from astrophysics to evolutionary history. My education is only enough to tell me that I don’t have a clue. Just look at other planets, they all have differently colored skies due to different factors, which could also affect Earth at other points in time.
That’s the best explanation of Rayleigh scattering I’ve seen in a while, thank you!
The interesting questions start at the next layer. For example, the same Rayleigh scattering could also lead to a violet or purple sky depending on the composition of sunlight. Or it could lead to an orange sky if the atmosphere was thicker and most of the blue got scattered into space. Or it could be all sorts of other colors due to atmospheric gases or dust. At long timescales, all these factors can change a lot. So if I try to convert the simple explanation into a prediction—“Daddy, was the sky always blue? What color will it be in a billion years?”—my mind goes everywhere at once.