Subject:
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Why the sky is blue (was: Re: Libertarian SPAM (Propaganda))
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Newsgroups:
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lugnet.off-topic.debate
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Date:
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Tue, 19 Jun 2001 20:58:23 GMT
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Viewed:
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1585 times
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In lugnet.off-topic.debate, Shiri Dori writes:
>
> Yep... the molecules in the atmosphere are the ones causing the sky's blue
> appearance. That's also why the sun appears yellow on the background of the
> sky (blue and yellow are complementary/opposite on the RGB scale, which is
> what our eyes use). In outer space, in near-vacuum, nothing reflects the
> light; the sky is black and the sun is white.
Well... the colour of the Sun will be subjective to how each individual
perceives colour, but it's peak output definitely lies in the range
that most people would call yellow. It is a whitish-yellow, because the Sun
also radiates at all other wavelengths.
The Sun (and stars and other celestial objects) really do have colour. If you
look at the night sky, all the little points of light look white. If you
stare long enough, Betelgeuse (which is cooler than the Sun) will appear red
and Sirius (which is hotter than the Sun) will look blueish.
> As for ocean and lake water - they are blue because of the sky's reflection.
> Not the other way around (NOT the sky is blue because water reflects in it).
> Water in itself, if you look at a cup inside your house, is entirely clear.
Ah, but if you look at a cup full of air, it also appears clear. It just
takes a whole lot of air (or water) before it will look blue, because
very little of the blue light passing through the air (or water) is scattered.
If you look at a lake or the ocean on a completely grey day, it will still
appear blue. Here is an experiment: If you fill a white bathtub, you can
usually see a bluish tinge in the water. (caveat: this experiment is not
guaranteed to work with heavily fluoridated water)
Another experiment: Look at a tree-covered hill off in the distance. Now
look at another tree-covered hill even further off in the distance. If the
air is fairly clean, the more distant hill will appear bluer because of the
larger amount of air between it and the observer.
Jeff J
(Self-annointed anal-retentive king of radiative transfer)
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Message has 2 Replies:
Message is in Reply To:
 | | Re: Libertarian SPAM (Propaganda)
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| (...) Yep... the molecules in the atmosphere are the ones causing the sky's blue appearance. That's also why the sun appears yellow on the background of the sky (blue and yellow are complementary/opposite on the RGB scale, which is what our eyes (...) (23 years ago, 19-Jun-01, to lugnet.off-topic.debate)
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