Colors of the world around us: Difference between revisions
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* '''The sky''' | * '''The sky''' | ||
: ...blue due to the nitrogen and oxygen. Their molecular size just happens to have a significant effect on blue (see [https://en.wikipedia.org/wiki/Rayleigh_scattering Rayleigh scattering]). | : ...blue due to the nitrogen and oxygen. Their molecular size just happens to have a more significant effect on the EM frequency we call blue (see [https://en.wikipedia.org/wiki/Rayleigh_scattering Rayleigh scattering]). | ||
: Since it's scattered, it's a diffuse effect throughout the whole sky. It's bluer when you look primarily at scattered light, as any other effects tend to be less pronounced. | : Since it's scattered, repeatedly, it's a diffuse effect throughout the whole sky. It's bluer when you look primarily at scattered light, as any other effects tend to be less pronounced. | ||
* '''Sunsets''' are red, and more so around the sun, | * '''Sunsets''' are red, and more so around the sun, actually for much the same reason | ||
: that is, when you look at a sunset, you are looking at the horizon, seeing light that has passed through more atmosphere - so has more of its blue scattered out, leaving relatively more red | : that is, when you look at a sunset, you are looking at the horizon, seeing light that has passed through more atmosphere - so has more of its blue scattered out, leaving relatively more red | ||
: it helps that we're looking almost directly along the original light path; that's the direction where mostly the unscattered rays are visible | : it helps that we're looking almost directly along the original light path; that's the direction where mostly the unscattered rays are visible | ||
: pollution also helps | : pollution also helps somewhat | ||
With little background, it is quite sensible to theorize that the reason that the sky is blue might be refraction. | |||
With little background, it is quite sensible to theorize that the reason that the sky is blue might be refraction. Water droplets, perhaps. | |||
It's not, though. | It's not, though. | ||
If it were, direction would matter a lot | If it were, direction would matter a lot more than it does - we would see different colors depending on where we are, | ||
and it would probably be almost entirely dark from behind us, opposite the sun. | and it would probably be almost entirely dark from behind us, opposite the sun. | ||
It's a sensible theory because this is less obvious than it may seem {{comment|((refraction in water droplets is a little more interesting than you might think)}}. | |||
Yet it's blue everywhere, fairly evenly. | Yet it's blue everywhere, fairly evenly. | ||
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Yes, but there's a lot of assumptions in there that | Yes, but there's a lot of assumptions in there that seem to add up to "...but not by much in a lot of practice". | ||
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One question is whether we could survive. | One question is whether we could survive. | ||
Another is whether eyes wouldn't naturally be selective in a similar 'looks like uniform spectrum to me' even though it isn't - | Another is whether eyes wouldn't naturally be selective in a similar 'looks like uniform spectrum to me' even though it isn't - the same is true for us with our sun. | ||
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Different gases might lead to other colors, | Different gases might lead to other colors, | ||
but there are relatively few gases which would have a significantly different effect | but there are relatively few gases likely to be abundant, most will be molecular gases so fairly small, | ||
and relatively few which would have a significantly different effect (TODO: back that). | |||
And if we want to not die from the atmosphere's contents, there's much tighter constraints. | And if we want to not die from the atmosphere's contents, there's much tighter constraints. | ||
Pressure also has an | Pressure also has an influence, but again, not so much in the range where human bodies want to live. | ||
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If we're talking Rayleigh scattering, | If we're talking Rayleigh scattering, | ||
we might get more or less of it of it, | we might get more or less of it of it, | ||
but this is mostly going to give us brighter or darker blues skies, not | but this is mostly going to give us brighter or darker blues skies, | ||
not wild colors within human-visible range. | |||
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Mars looks red, but not because of its atmosphere - the martian atmosphere is so thin that the Rayleigh components is tiny (TODO: figure out | Mars looks red, but not because of its atmosphere - the martian atmosphere is so thin that the Rayleigh components is tiny (TODO: figure out Rayleigh on CO2 - it seems to do the same, but the low pressure makes it less significant{{verify}}), so actually a clear martian sky looks almost black. | ||
But a clear sky is rare. | But a clear sky is rare. | ||
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: '''So is the sea blue for the same reason?''' | : '''So is the sea blue for the same reason?''' | ||
Well, partly it's just that | Well, partly it's just that we almost always look at the sea at such a shallow angle that most of what we see is reflection, | ||
And most of that reflection is from near the horizon | and the sky is blue. | ||
This is also why polarization filters help look into water and | And since most of that reflection is from near the horizon and there's likely some clouds involved, often a lighter blue. | ||
This is also also why polarization filters help look into water, and make any color of the water seem a little more intense. | |||
...because yes, the water is also blue by itself. | |||
Which is how it can appear a deeper blue than just reflected sky could explain. | |||
And indeed, this is basically Rayleigh scattering too. The mechanics are slightly different, e.g. that being a lot more matter, | And indeed, this is basically Rayleigh scattering too. The mechanics are slightly different, e.g. that being a lot more matter, | ||
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Pools of water, and seas near the shore are usually be the color of what's suspended in there, e.g. [http://en.wikipedia.org/wiki/Colored_dissolved_organic_matter dissolved organic matter] or much we put into a nearby river, or just sand. | |||
Very clear and at least moderately deep water will be dominated by, well, the absence of that. | Very clear and at least moderately deep water will be dominated by, well, the absence of that. | ||
Latest revision as of 13:36, 9 October 2023
✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.
The sky
On sunsets
See also
Might other planet's skies be other colors?
The sun
(TEMPORARILY ELSEWHERE)