[Artifexian]: Good morning, Interweb! Question: do skies have to be blue and plants green? [Artifexian]: Answer: not even slightly [Artifexian]: Quick recap: starlight is a mixture of various different wavelengths of light. [Artifexian]: When light hits stuff in an atmosphere, these wavelengths get scattered. [Artifexian]: If that stuff is really small, shorter wavelengths of light are scattered more efficiently. [Artifexian]: We call this Rayleigh Scattering. If that stuff is relatively big, all wavelengths of light gets scattered equally. [Artifexian]: We call this Mie Scattering. Our sky is blue because of Rayleigh Scattering and our clouds white, [Artifexian]: because of Mie Scattering. [Artifexian]: The warm-coloured skies of Twilight occur because the more atmosphere light passes through, [Artifexian]: the more the shorter wavelengths of light are scattered away, [Artifexian]: leaving only the longer, redder wavelengths of light to hit our eyes. [Artifexian]: Oh! And speaking of eyes, unless otherwise stated if I say something is a certain colour, [Artifexian]: I mean that with respected to the human eye in Earth-like, Nitrogen-Oxygen atmosphere. [Artifexian]: Got it? Cool. Let's world-paint. [Artifexian]: Take an earth-like, atmosphere add warm coloured gases to it-- boom! Warm-coloured skies. [Artifexian]: Extremely high concentrations of Methane and Ozone will tend to sky a hazy, orangey-reddish colour. [Artifexian]: Nitrogen-Oxide would produce an orangey brown sky. [Artifexian]: Sulfur gas will make for yellow skies or red skies, depending on the temperature of the atmosphere. [Artifexian]: And there's probably a whole ton more warm-coloured gases out there. [Artifexian]: Unfortunately, most, if not all of them, will be super, super toxic to carbon-based life-forms. [Artifexian]: Alternatively, we could suspend coloured particles in our atmospheres. [Artifexian]: In 2017, Saharan dust and Spanish smoke blew over the UK, turning her skies orange and her sun blood-red. [Artifexian]: Obviously, a temporary phenomenon. [Artifexian]: But for something more lasting, we can look to Mars. [Artifexian]: Winds on Mars continually blow a fine Iron-Oxide dust into its skies. This dust absorbs blue light, [Artifexian]: so the Martian sky is butterscotch each early day and pinky-red at twilight. [Artifexian]: Interestingly, around the setting sun, [Artifexian]: the sky is blue, which is like anti-Earth? Again, a consequence of the dust in the air. [Artifexian]: So there's two methods: coloured gases, coloured particulates. [Artifexian]: But we can also let Scattering alone do the job. [Artifexian]: Take an Earth-like atmosphere, [Artifexian]: make it significantly thicker-- boom! Warm-coloured skies. [Artifexian]: By increasing the thickness of an atmosphere, and by extension the pressure, [Artifexian]: we're essentially taking twilight conditions [Artifexian]: and applying them to the whole sky. [Artifexian]: We can very, very roughly estimate the thickness needed to achieve this [Artifexian]: by doing a bit of trig on the angle subtended by the twilight zone-- don't worry, [Artifexian]: I'm not gonna bore you with the maths. There's a spreadsheet in the description. [Artifexian]: The important point here is that as atmospheric thickness increases, the sky will get redder, [Artifexian]: brightness will go up, and saturation will go down. [Artifexian]: That is to say, very, very thick atmospheres will yield pale, de-saturated, reddish skies. [Artifexian]: Lastly, the easiest solution is perhaps to vary the star. [Artifexian]: A sky colour is also dependent on the standard temperature. [Artifexian]: Cool, low-mass stars will output most of their light in the red, [Artifexian]: Massive, hot stars will output most of their light in the blue. [Artifexian]: So, the bigger the star, the bluer, brighter, and more vivid the sky. [Artifexian]: The smaller the star, the redder and dimmer the sky. [Artifexian]: Basically this: (Music) [Artifexian]: That said, some argue that this is wrong, asserting that regardless of stellar class, skies will always be some shade of blue [Artifexian]: given how dominant blue Scattering is. [Artifexian]: Kind of like this: (Music) [Artifexian]: Basically, choose at your own peril here. [Artifexian]: Assuming the first scenario, the transition zone between K and M stars will yield white-ish skies. [Artifexian]: The denser the atmosphere, the purer that white. [Artifexian]: Oh, and clouds on such a world would reflect any un-Scattered light, [Artifexian]: thus appearing yellowish or reddish. [Artifexian]: A sky full of large, colourless particles will also appear white-ish as Mie Scattering will dominate. [Artifexian]: Heavily polluted planets could have milky whitey, grey skies. Or more obviously, [Artifexian]: planets with large amounts of cloud cover could have permanently overcast white, grey skies. [Artifexian]: Black skies are easy: No atmosphere no colour. [Artifexian]: The star would be a pure white colour and will be bright enough to limit the visibility [Artifexian]: of background stars. The further out the planet orbits, the more background stars would be visible. [Artifexian]: Green is...tricky. [Artifexian]: Remember, high mass stars skew blue, low mass stars skew red. [Artifexian]: Somewhere in the middle then there's a start of peaks in the green. So green skies, right? [Artifexian]: Nope. [Artifexian]: See, in human eyes green will always either combine with red to give yellows and oranges, [Artifexian]: or blue to give cyans. [Artifexian]: Even at peak green, there's enough of the other wavelengths about to prevent a pure green sky colour. [Artifexian]: That said, Alien eyes could work differently. [Artifexian]: Coloured gases are, of course, an option. Chlorine would tint the sky a yellowy-green colour. [Artifexian]: Or at high enough concentrations a yellow-green black colour. See, chlorine is a really good absorber of light, [Artifexian]: so the more chlorine, the darker the surface conditions. [Artifexian]: Oh, and it's super toxic. [Artifexian]: But, it could work. We could do a Mars, invent some green dust, and suspend them in the atmosphere [Artifexian]: If not dust, then maybe airborne plant-life. Think sky-algae or sky-plankton. [Artifexian]: Introduce bio-luminescence, and your sky will be a green-tinted acid trip. [Artifexian]: Think biologically created auroras. [Artifexian]: Auroras provide temporary coloration. When charged solar particles hit the atoms in the atmosphere, [Artifexian]: they excite those atoms and light is given off. M stars are a class of star prone to massive solar flares. [Artifexian]: Solar flares mean more charged particles. More charged particles means more frequent, more vibrant, and more extensive auroras. [Artifexian]: Also, if a planet's atmosphere is packed with Neon or Sodium gas, say, [Artifexian]: these auroras will be orangey-red or yellow, respectively. [Artifexian]: And finally, [Artifexian]: there's the Green Flash. [Artifexian]: When conditions are just right, the Sun flashes green as it sinks below the horizon at sunset. [Artifexian]: On Earth, this effect is really rare and fleeting. [Artifexian]: But if a planet rotate at a much slower rate, this green flash could become more of a nightly green glow. [Artifexian]: Think Pirates of the Caribbean, except way less extra. [Artifexian]: So, shorter wavelengths of light are scattered more right? Then why is our sky blue? [Artifexian]: I mean, violet light has a shorter wavelength than blue light. [Artifexian]: Shouldn't our sky be violet? [Artifexian]: Turns out it kind of is, we just can't see it. [Artifexian]: That's 'cause the Sun emits less violet light then blue light, [Artifexian]: and our eyes are not as sensitive to violet as they are to blue. [Artifexian]: So where we see blue, an alien may well see violet. [Artifexian]: In 1950, the Sun over British Columbia turned to "various shades of blue or violet" The culprit? [Artifexian]: Forest fire smoke. Same shtick happens with literal blue moons. [Artifexian]: Diurnal cycles aside, [Artifexian]: Wouldn't it be cool if sky colour varied regularly [Artifexian]: and predictably? Kind of like our Sulfur atmosphere from before: yellow skies in winter red skies in summer. [Artifexian]: Assuming of course, the correct temperatures are hitched. But another cool solution is to have an Earth-like world orbit close, binary stars, [Artifexian]: where each star differs significantly in mass, A.K.A., temperature. [Artifexian]: So as they eclipse one another, the sky would suddenly change colours. [Artifexian]: Perhaps pale blue [Artifexian]: to white [Artifexian]: to pale orange. [Artifexian]: Anyways, onto plants. [Artifexian]: Remember, stellar output peaks in certain frequencies and colours, [Artifexian]: so we have two floral options: plants that are the same colour as a star's peak output [Artifexian]: or the complement to that colour, like if a star outputs predominantly in the blue, plant life could either be bluish or [Artifexian]: yellowish. Yellow plants are kind of saying "Okay. I need starlight to live, [Artifexian]: so let me take in the most starlight I can in the most efficient manner possible." [Artifexian]: Whereas blue plants are saying "Look, all that peak radiation may be damaging to me, [Artifexian]: so I'm going to block it and just feed off the other wavelengths instead." [Artifexian]: Both strategies could potentially work. [Artifexian]: Here's a rundown of strategy A: (Music) [Artifexian]: And here's a rundown of strategy B: [Artifexian]: Also, there's a colour calculator in description, so go check that out. [Artifexian]: In both cases, [Artifexian]: I've made the plans whitish around high-mass stars and black around low-mass stars. Very massive stars output [Artifexian]: so much radiation. that a plant will likely want to reflect back as much of it as possible, [Artifexian]: lest it burn. Very low-mass stars output [Artifexian]: so little radiation that a plant will want to absorb as much as possible, lest it starve. [Artifexian]: Unless, of course, those stars are Flare Stars, in which case the low radiation output will be punctuated by [Artifexian]: bursts of massively increased radiation. [Artifexian]: Not good news for plant-life! [Artifexian]: Especially black plant-life: those plants would need to develop an early warning system, [Artifexian]: some sort of UV detector, perhaps. [Artifexian]: and the ability to take cover. That might mean evolving a shell-like structure they could withdraw into [Artifexian]: or maybe burrowing abilities or maybe they literally move, [Artifexian]: blurring the line between plant and animal. [Artifexian]: Or maybe plants in such a world would need to live underwater, the water acting as a shield. [Artifexian]: Basically a dimly lit, orangey-red and black swamp world. Pretty cool, right? [Ewa]: That is pretty cool, [Ewa]: but I really like the idea of a seasonally changing sky. [Ewa]: so let's say we have a large continent with a tall mountain range all along its western and [Ewa]: southwestern flanks. The center of the continent is a giant desert, [Ewa]: and in winter a powerful monsoon wind blows from the interior towards the coasts. [Ewa]: There's a great city in the south and during the winter monsoon, the sand blown from the great desert fills the air [Ewa]: and paints the sky red. The red season is also the dry season and as it continues, [Ewa]: rivers and watering holes start to dry up, [Ewa]: so the people of the city bring outeverything blue they own into their courtyards and into the streets [Ewa]: to change the colour of the sky. And in the city center atop the main temple, [Ewa]: they turn the sacred bellows north to reverse the direction of the wind [Ewa]: Summer comes eventually and the monsoon winds start to blow from the sea to the interior, [Ewa]: bringing with them a blue sky as well as clouds and rain. [Ewa]: Rivers fill with water, people plant their crops, and cows give birth to calves. [Ewa]: But along with renewing, life the southern winds also bring death. [Ewa]: stagnant pools of rainwater turn into breeding grounds for mosquitoes, [Ewa]: and the insects transmit malaria and dengue fever, killing many people. [Ewa]: And so everyone brings out their red clay pots and puts on their red clothes to banish the blue sky and its clouds [Ewa]: while the sacred bellows are turned to point south to call upon the desert winds. [Ewa]: And with time, the winter monsoon comes and fills the air with sand, [Ewa]: painting the world red until it's time to turn the bellows again. [Artifexian]: Good morning interweb! A massive, massive, massive [Artifexian]: Thanks goes out to Ewa of WorldbiuldingNotes for collaborating with me on this video. [Artifexian]: She is an amazing creator and deserves so many more views than she currently has, [Artifexian]: so, please, please, please go over there and blast her page. I promise you, you'll love her content. [Artifexian]: Also a massive thanks goes out to Simon Clark, another Youtuber who you will love, [Artifexian]: For helping me out with some of the science in this video. And finally a massive [Artifexian]: Thanks goes out to each and every one of you for watching this video and supporting artifexian. In particular, [Artifexian]: I wanna shout out. Isaac Silbert, Andrew Chehayl, Robin Hilton, World Anvil, Ripta Pasay, John Hooyer, and [Artifexian]: new top-tier patron, A.E. Stephenson. You all are absolutely amazing. Until next time, Edgar Out!
This was a great one! Iām glad to see two of my favourite YouTubers collaborating. I hope I can see more collaborations in the future!
Not really related, but this is where you're most likely to see this- I'm a linguistics major, and my professor in my syntax class showed your "English Has No Future" video when we started talking about tense!
On the twilight point, I'm curious of how a sunset would appear on other worlds. Sun type and atmosphere obviously contribute, but how? What's the science behind sunset colors?
Yay! I made this happen! Meee! :D
The point about flare stars and black plants is interesting, as living worlds around M-type stars are almost certainly tidally locked. Plants would evolve with one side sensitive to the sun and keep facing toward it around the clock, for weeks or years at a time between flares, so they would also have a side that never gets direct light. That side could evolve the components of a protective shell to snap closed at first hint of a flare, or perhaps the entire plant twists, coils, or lays flat to turn its 'dead' side to the light.
ooh gotta watch this after Iām done meeting with classmates.
That was cool. It'd be interesting to go into the relationship between colour and atmospheric composition in a little more detail as well, especially with regards to the Designing Earth-like Atmospheres video from last year.
How do you go about calculating the greenhouse effect of an Earth-like atmosphere? Using your spreadsheets so far, I've got to make my planet's atmosphere quite thick to trap enough warmth in just to get it to an Earth-like temperature: if I make the atmosphere the same as Earth's, the average temperature is a chilly ā35Ā°C.
I'm not sure I buy that the sky under a very thick atmosphere would appear red. If the sun is overhead rather than at the horizon, would the blue light all scatter back into space without reaching the ground? Or would it just be red near the sun, but still blue from scattered light farther away?
What about airborne plants that change color depending on the season?