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[–] 135 points 3 weeks ago (19 children)

I liked a version of this (I believe) XKCD said once.

A perfectly valid response to the question, "why is the sky blue?" is simply, "because air is blue."

Yes, you can give a lot of explanation about refractive index and Rayleigh scattering. But all this does is provide details of how light interacts with air. And the same reason anything is the color that it is is due to the way it reflects, transmits, or absorbs light. You're citing real scientific principles, but you're ultimately just explaining why air is blue.

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  • [–] 79 points 3 weeks ago

    It's a very good relevant XKCD.

    The title text is more directly applicable: If you ask "why are leaves green?" the usual answer is "because they're full of chlorophyll, and chlorophyll is green," even though "why does chlorophyll scatter green light?" is a great question too.

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  • [–] 22 points 3 weeks ago (4 children)

    "Don't breathe air, it has sharks in it! BLUE HAS SHARKS IN IT!" -The funny purple man

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  • [–] 17 points 3 weeks ago* (10 children)

    But it's an incomplete answer.

    "air is invisible at short distances, blue at longer distances, and takes on red green and orange at sunset" would be better

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  • [–] 28 points 3 weeks ago (9 children)

    The same is true for all colors. Tell me the color of a single atom.

    Yes, air can be colors other than blue at unusual light conditions, like sunset. But the same is true for any material.

    You're stuck on the urge to explain. You call "the air is blue" incomplete. But all answers are incomplete. When someone asks what color an object is, they mean under ordinary distances and conditions. Air is blue even in an ordinary room. It just takes miles worth of air for its slight blue color to be noticeable.

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  • [–] 98 points 3 weeks ago* (14 children)

    The crazy part is the exact science behind why plants reflect green specifically is still debated. One theory is that, because much of the sun's energy is released on that wavelength, controlling for it specifically allows the plant to better manage energy fluctuations (highly simplified but you get the idea)

    longer explanation and sourcePlants are green specifically because the red and blue wavelengths of light are useful for breaking specific chemical bonds necessary for photosynthesis and as such are readily absorbed by the plant. The plant makes efficient use of the energy provided by only absorbing the wavelengths necessary for its processes. However, plants still absorb 90% of green light and green light holds the highest proportion of the energy radiated by the sun.

    To be more clear, green light has too much energy. When plants absorb light it first enters a protein mesh containing pigments such as chlorophyll that function like an antenna or receiver for a range of wavelengths. The pigments then transfer the energy to a "reaction center" where it turns this electromagnetic energy into chemical energy (photosynthesis). This process is exceedingly efficient; almost all of the absorbed energy is converted into electrons the plants can use. However, this protein mesh antenna is not solid and is constantly moving. These movements affect how energy is absorbed and how it flows through the pigments. Think of diffraction in water. Fluctuation in the intensity of light can create noise in this process; a quick brush of shade or sudden increase of light intensity can decrease the efficiency of photosynthesis. For plants and really everything that lives, a steady input and output of energy is desirable. Not enough electrons making it to the reaction center causes energy failure while too much will cause general overcharging effects that can damage tissue. When the noise of this system fluctuates it makes it difficult for the plant to self regulate it's energy flow and could cause the plant to kill it's own tissue or essentially starve. So essentially, while absorbing all green light would provide the plant with more energy, it's not capable of handling this energy so plants evolved to limit their intake of green light.

    However, this is not to say that green lights ability to efficiently evaporate water is not a factor in this evolutionary development, hell it's probable that these two things are heavily related. Green light might evaporate water so well because of some combination of its relatively high energy mixed with the size of its wavelength interacting with the hydrogen bonds between water molecules in a more efficient manner than other wavelengths of electromagnetic radiation.

    source for those interested

    this is a copy pasted comment from this post and as such not every part of it has context

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  • [–] 16 points 3 weeks ago (8 children)

    So why are some plants purple?

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    [–] 66 points 3 weeks ago (3 children)

    “Incandescent rage” is one of those phrases I have pocketed for a future conversation.

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  • [–] 39 points 3 weeks ago (12 children)

    Except the sun isn't yellow, it's white with a slight bias towards green.

    Want to check, put something white outside, it looks white, not yellow.

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  • [–] 50 points 3 weeks ago (5 children)

    The reason the sun appears to be yellow is the same reason that the sky appears to be blue.

    Blue light is scattered more by the air in the atmosphere than other wavelengths. Remove blue from white light and you get yellow. So the light coming from the sun that isn't scattered and dispersed through the sky (making the sky look blue) is yellow.

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    [–] 36 points 3 weeks ago (11 children)
  • [–] 77 points 3 weeks ago (3 children)

    That's from plants that get their air mostly from the shade and sunsets, so obviously they'd be less yellow and more dark and red.

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  • [–] 6 points 3 weeks ago (5 children)

    There's also an extremely tiny percent of plants that are entirely white, they don't get their energy through photosynthesis but instead a parasitic relationship of fungi and other plants.

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  • [–] 6 points 3 weeks ago (3 children)

    Mycoheterotrophs! Love them, such bizarre little plants

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    [–] 14 points 3 weeks ago (20 children)

    Whinging about a fact being wrong without providing a correction is worse than the one being wrong.

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  • [–] 10 points 3 weeks ago (3 children)
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    [–] 5 points 3 weeks ago

    Science is making mistakes towards to the truth

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  • [–] 5 points 3 weeks ago (11 children)

    I'm still not following. What part of "blue air" imparts chlorophyll with its color? I get the sun. I understand how light works (reflection, refraction, and scattering). I understand our perception of light on a neuological level (including post-processing) to an extent that most people haven't studied. Why "blue" air make green plant?

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