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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.
Better question: “Why is the sky usually blue but sometimes red?”
Talking specifically about sunsets, not apocalyptic wildfire smoke
Incidentally it’s the same reason between a sunset and smoke - more scattering.
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 source
Plants 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
“Incandescent rage” is one of those phrases I have pocketed for a future conversation.
I mean, technically they weren’t wrong.
Purple leaves are a thing.
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.
Mycoheterotrophs! Love them, such bizarre little plants
I was so disappointed when I learned how hard (I mean I haven’t actually tried it) to culture them, but it makes sense given how they occur.
Yeah I wouldn’t try that in a million years, you need, like, an actual functioning ecosystem for them to flourish
As is purple rain.
Whinging about a fact being wrong without providing a correction is worse than the one being wrong.
The thing is it’s kinda right, just lacking detail
Cab you help explain it? I thought that the sky was blue because it reflects the ocean and because of rayleigh scattering, but do either of these affect the color of plants?
You’ve got it partially backwards. The sky is blue because of Rayleigh scattering, but it doesn’t reflect the ocean; the ocean is blue because it reflects the sky.
Incidentally, I’ve heard it said (I think it was xkcd) that we use the term “Rayleigh scattering” because it sounds silly to say that the air is blue (via the mechanism of Rayleigh scattering); so maybe that’s part of it?
The bit about the ocean being blue because it reflects the sky is unfortunately mostly wrong. Water is slightly more blue than ozone, so the more of it there is (big water in big ocean) the more blue it will look. The fact that it’s also reflecting the blue sky adds to the color, but on a cloudy day the ocean is still blue.
I’m about a kilometer from the ocean right now (I’m standing in front of the window through which I can see it), and it’s a partly cloudy day. When the sky is clear (as it was five minutes ago), the ocean is a rich, saturated blue or even teal. When it’s cloudy (as it is currently), I can see that it’s a cool gray color. I might call it a very dark, desaturated cyan at most. So from my observation it has to be the opposite: the relative blueness of the ozone and the water must be the less dependent factor, and the color of the sky the more dependent one.
It’s tricky, though. I guess I might be in a place with weird salinity or plankton or something.
This is kinda away from the other replies to your comment. But I took that meme as saying plants get CO2 from the air (blue - scattering) and use sunlight (yellow - not really but meh) to produce many things with it, including chlorophyll which is the green pigment in plants.
Plants are green because they absorb all other wavelengths of light. And bounce the green into your eye. In actual fact, color only exists in your brain as a way to understand the world around us. Our eyes are just sensors that detect light. And color is how we process it. We could have evolved into understanding it in different ways too, like smell. Therefore color doesnt even exist in the natural world. Green is just an illusion of our mind.
Color exists physically as different wavelengths of light. The thing “in your mind” is about non-natural colors which trigger multiple light cones in your eye and your brain interprets them a certain way different than the natural colors. In that sense you do interpret the wavelengths one way or another in your head, but the actual light wavelengths so exist.
Yeah wavelengths exist. But ALL color only exists in your mind as perception. Natural and non natural.
If color existed outside of light touching your eye, you would be able to deduce it without light.
Fun to think about.
Sky isn’t yellow over a cornfield
This is indeed a valid theory, but not very powerful since it can only explain the color of green plants and not for example the color of non green plants or animals.
More powerful theories have been developed which can work on a much broader range of applications. For example the theory that plants are the color they are because God painted them that way.
Plants look green because the green spectrum has a lot of energy, and to stop over heating and leaf burning and messing with the delicate photosynthesis, plants reflect or let green mostly pass through and only use about 20% of green soecturm energy, while mostly use all of red end and blue end… At least that’s what I heard on a science show.
And why does the green spectrum have a lot of energy?
I’d have to go back and find the science article, but it was something about sunrise, sunset which would often provide end of spectrum red or blue, while full daylight provided a lot of green light spectrum. Plants having to balalnce processes in full spectrum would overload/oveheat so they evolved to reflect or transmit through 80% of that spectrum.
They mostly use red and blue for photosynthesis because those seem more steady during daylight hours in various seasons and hours of the day. Cloudy day still gets infrared end through etc.
The green overlaps into red and blue zones. Its not so much that it is higher energy than blue, but a wider amount of spectrum total energy the plant wants to avoid.
Explain this then
Because evolution isn’t actually guided and is really just a process of mutation, reassembly (for sexual species), then checking to see if it works well enough to pass genes on. Apparently red leaves work for that plant
We have diverse geography, and genetic diversity. Obviously this plant worked out a way to use the high energy of the wide green ranhe, without overcooking itself. But if you compare all plamt leaves and grasses of plant life green is the most common.
Science is making mistakes towards to the truth
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?
Mix blue and yellow paint and you end up with green paint.
Oh, damn. Reductionist.
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