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  1. #11
    Trask's Avatar
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    Actually, pollution plays a part as well, as particles can affect the color of light in sunsets. Interesting story: the famous painting "The Scream" has a strange set of background colors that look imaginary. But the artist painted it in northern Europe some months after Krakatoa blew and threw tons of dust into the world's atmosphere. This resulted in strangely-colored skies and sunrises/sunsets in many locations around the world, including in Europe.

  2. #12

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    *putting on my atmospheric physicist hat* The previous respondents have all given you bits and pieces of what's happening so, let's summarize for clarity.

    Photons obey Newton's first law just like anything else and travel in a straight line unless forced to do otherwise. However, even when looking straight at the sun, the chance that any photon reaching your eye (or other photosensitive medium) has gone straight from the sun to your eye without scattering off something is incredibly small. After sunset, that chance is zero.

    Describing what happens between the sun and our eyes falls under the study of radiative transfer which ends up being all about the subtleties of what stuff is between the sun and you and how it interacts with electromagnetic radiation. A lot of that subtlety has to do with how large the stuff doing the scattering is compared to the wavelength of light that is being scattered. Light scattering off gas molecules (scatterer size about same as wavelength of light) gives us the blue daytime sky: short wavelengths (blue) scatter more than longer (red) so the red stays in the straight line path away from the sun and the blue gets scattered out of the beam and into our eyes (from virtually all angles away from the sun). At sunrise/sunset, we are looking at the sun so this same effect scatters blue out of the beam and away from our eyes leaving enhanced red color to reach our eyes. Blue daylight and red sunsets are the same phenomenon just viewed from different angles.

    Light scattering off larger particles (aerosols, dust and water droplets) gives rise to scattering that is generally less wavelength dependent. Notable exceptions are fine dust which tends to help redden sunsets and large water droplets (rain) which produces rainbows. Most of what changes here is how the intensity of light is distributed angularly in a beam of light coming from the sun. Large aerosols tend to scatter photons more forward in the beam and less out of the beam (you can think of this like focusing the beam, although that is not really what is happening). This is the source for the bright, white aureole around the sun during the daytime: dust and aerosol in the atmosphere forward scatter the entire spectrum making a white-ish, bright area around the sun. Compare the area of sky near the sun on several different sunny days with different humidity and different air quality forecasts. Cleaner, drier days should show much less whitening near the sun.

    Anyway, this merely scratches the surface. Like I said, it all becomes about the subtleties and that is why we should all spend more time admiring sunrise and sunset.
    "A friend will bail you out of jail.
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  3. #13
    Ian Grant's Avatar
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    Quote Originally Posted by snallan View Post
    It seems the ancient Greeks did not have a great need for naming colours, indeed they often referred to the sky as being "bronze".
    Quote Originally Posted by Edward_S View Post
    Homer (and I don't mean Homer Simpson) thought the Aegean was 'wine dark'. What colour is your wine, just out of interest?

    Well some of the ancient Greek glass-ware in the museums is pale green-blue, so maybe not far off the colour of the Aegean when filled with white wine U usually drink the local Red wine though.

    The sky's often Zone V here, rather deep Blue

    Ian

  4. #14
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    Quote Originally Posted by Edward_S View Post
    Homer (and I don't mean Homer Simpson) thought the Aegean was 'wine dark'. What colour is your wine, just out of interest?
    There is a strong bias toward red in this household, and within that range it varies. It is probably generally darker than the wine Homer drank, though I am not sure whether in 1000 BCE - or whenever he lived; I don't think anybody's really sure - the Greeks practiced watering their wine. They did so during the classical period, when to drink your wine "neat" was apparently considered vulgar. Seems to me I got this from Thucydides. It has been something like 50 years since I studied it.

    Homer also thought (at least as translated by Richard Lattimore) that dawn has rosy fingers.

    Quote Originally Posted by Curt View Post
    The question that follows this one would be: "What color is the ocean?"
    While water has a very slight blue-green color (you'd need a lot of it to really notice it) the main influence on the color of the ocean is the sky, which is reflected by the surface. So, one might ask, further, why is it always darker than the sky? Light from the sky is not polarized, but what's reflected by the surface is. So, the ocean surface is a little less than 1/2 as bright (like your polarizer's filter factor) as the sky.

    Variations occur that may make the surface appear to be markedly different from the reflected sky above it. One reason (I suspect it is the main influence) is that the surface of the ocean is not just like the mirror in your bathroom. It has ever-changing facets, each of which (millions, billions) is reflecting a different location in the sky. To complicate matters further, each of these facets reflects light that is polarized in it's own peculiar plane, so the polarization is, in the aggregate, an extremely complex dance. It could appear that there is a near complete compliment of planes, but that isn't at all the same as the unpolarized light coming directly from the sky.

    Isn't stuff like this fun? Thanks sbuczkowski for the very informative contribution!

    Larry Bullis
    Anacortes, WA: where there's LOTS of water reflecting lots of sky,
    especially covered with clouds much of the time, but when it's sunny
    there's an amazing amount of really gorgeous blue.
    Last edited by bowzart; 06-30-2010 at 10:01 AM. Click to view previous post history. Reason: add thanks

  5. #15

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    Quote Originally Posted by Trask View Post
    Interesting story: the famous painting "The Scream" has a strange set of background colors that look imaginary. But the artist painted it in northern Europe some months after Krakatoa blew and threw tons of dust into the world's atmosphere. This resulted in strangely-colored skies and sunrises/sunsets in many locations around the world, including in Europe.
    Thanks for reminding me of this! If anyone is interested further, you can read the Sky & Telescope magazine article here:

    http://ecommons.txstate.edu/cgi/view...ntext=physfacp

    Quote Originally Posted by Ian Grant View Post
    Well some of the ancient Greek glass-ware in the museums is pale green-blue, so maybe not far off the colour of the Aegean when filled with white wine
    Hmmm... interesting thought!

    Quote Originally Posted by bowzart View Post
    Isn't stuff like this fun? Thanks sbuczkowski for the very informative contribution!
    Yes it's fun; I quite enjoy this kind of thing.

    Edward.

  6. #16

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    Quote Originally Posted by bowzart View Post
    There is a strong bias toward red in this household, and within that range it varies. It is probably generally darker than the wine Homer drank, though I am not sure whether in 1000 BCE - or whenever he lived; I don't think anybody's really sure - the Greeks practiced watering their wine. They did so during the classical period, when to drink your wine "neat" was apparently considered vulgar. Seems to me I got this from Thucydides. It has been something like 50 years since I studied it...
    Homer meant that the sea was dark as the (red) wine. The fine detail is that there were two different words for two related things: οίνος - κράσος (oinos - krasos). Oinos, the word used in Odyssey, is the word for undiluted wine. Krasos (krasi in moder greek) is the word for the diluted.

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