If I asked an adult why the sky is blue and they answered: "Because the ocean is blue it reflects the light from the sun....": I don't think I would ask them any more questions.
Because god erased the rainbow and is colour blind and forgot the blue, otherwise it'd be dark all day. If it was up to me I'd not ask anyone anything. Look, I know a scientist, super smart guy, he says the sky is blue on a sunny day. He says it's red sometimes in the evening. And it should be purple, but we have trouble seeing violet, which isn't purple and the sky has no colour and purple isn't a colour but two and brains make us see things, not eyes, otherwise you'd be seeing red and blue. I understand that about half of the US is creationist or worse and has the mental capacity of a toddler, but I can assure you, there are grown ups in the world, some even in America. The sun doesn't rise or set, the planet rotates. What you observe isn't necessarily what the thing actually is. Next thing you know Fermilab is making videos of how the Earth is flat from up close and it changes shape if you go up high enough.
The water is the one that reflects. There are forest pools, where the water may be green, brown or almost black, because there is not much sky to reflect. Those other colors are usually far darker than the sky blue. Agaist a brick wall you may find even red water.
Kids are natural philosophers too. As a small kid I was always wondering things like "Why am I real", and "What is nothingness". Things that vex philosophers , and physicsts , to this day. Not that I had an answer, but yeah.
@@shayneoneill1506 Absolutely. Children's minds tend to be open, it's only as adults (as Einstein noted) that we develop the set of prejudices we call 'common sense'.
Isn't it weird how adults are meant to know enough to not ask the questions that could very well provide the answers we were searching for all along... Backward at coming forward, or so the saying goes.
@@_34_Lies Yep. I think it's partly because as adults, we're given to think that imagination is a bad thing, thinking differently is bad, and questioning accepted axioms is foolish. Fortunately, those rare individuals who make the big breakthroughs never lose that childlike wonder that lets them see further, differently, or something that is hidden from the rest of us.
@@Nigelrudyardmusic hopefully, it's not beyond our reach. If we can develop and nurture the courage to ask the right questions, so much more may be available.
I've heard this before, so I listened to see if anything had changed. The biggest change was that the human eye is imperfect at seeing the purple spectrum of light. I was expecting Dr. Lincoln to just walk off the screen with the VERY first explanation. and walk back on from the other side to finish the video!
Excellent, Don! This is the sort of thing I used to head down to the local library to find out in the late 1950s and 1960s. No Internet! When I got my first digital camera around 2002 and had to work out how to stop blue skies going purple. Now I know just why they went purple. Thanks! You should do more of these 'childhood-type' question videos if only to remind us where we came from. One of my earliest memories of working something out was realising aged two or three that wind wasn't caused by the trees waving around.
Same here for me but in the 1990s right before the internet came out. Having been born at he end of the 1980s, I’m the last generation to have known what it’s like to have had to rely on the library for all the answers to questions no one you knew could give you lol.
Wow, I was thinking "maybe digital cameras see the sky purple, but photos on my camera are blue, maybe it's a software correction", now I know some cameras really used to "see" purple, good to know that, thanks for sharing.
some of my earliest memories are of visiting fermi lab (my dad worked there)... floor 15 makes an impression. just found the channel today, but it seems like floor 15 is on youtube now (i mean, has been. the algorithm really failed me this time)... anyway, peter, i too vote for more "childhood-type" questions
...now I'd like to see how you explained Rayleigh Scattering to your daughter (I'm assuming, as your post was a day ago, that you are still explaining that part😉)
@@markzambelli I would say "air is made out small things and light is a bunch of small waves; the smallest waves bounce the most and spread out for us to see"
i think I got the sunset thing, but it is quite confusing at first (scattering blue light makes a blue sky, except for sunset, then scattering even more blue light makes the sky orange. what?). If you can see a picture from space, it helps. The blue being scattered means it can't penetrate as deep, as it goes in all kinds if directions rather than away from the sun.
at the low angle in the morning and in the evening, the light has to pass through more atmosphere. The light always scatters randomly in all directions. When it reaches you, most of the blue light has already scattered away from you. When the sun is higher, the light doesn't have to travel much to reach your eye. More scattered blue light reaches your eye.
Night stars appear then disappear Sun appears domineers our sphere Reflective light of day does appear Blue sky molecules in atmosphere No other planet so lucky is near
Thanks Doctor Lincoln. I remeber from school that critical opalesence was mentioned but cannot remeber what it is and if it plays a role here. I am sure you know. Keep up the good work
Fun fact, the sky is *not* blue, it is cyan. What you call "indigo" in the video is the actual color blue. Cyan sits somewhere between blue and green. The arrows at 3:37 should therefore read "red, orange, green, cyan, blue and violet".
There was one detail that slipped through. During those spectacular sunsets, what looks red-orange is the light reflected from the clouds and the sun itself. But the actual sky still looks blue. You can see it at 6:21.
Actually the red, orange and yellow colors appear in the clouds before they appear in the sky. If you pay close attention to the sky after sunset on a clear day the sky will glow yellow, orange and red before the darkness settles in.
I always feel there's a step missing in the explanation of Rayleigh scattering. If blue (and violet) light is being scattered more, then wouldn't it be scattered away from the observer? This would suggest that the sky should always be orange/red not just at sunrise and sunset. I've never found a decent explanation to fill in that gap between blue light scattering and more blue light reaching the observer.
I think you have to think of it as being scattered toward you and not being scattered away from you. Because if the other colors just go straight down while blue is coming to you from all directions because of the scattering, then naturally you're gonna see more blue than the other colors, but only if the medium is short enough. If the medium is getting longer then you start having less and less blue light left to be scattered around and the other colors overtake. But I might be wrong, please restate Marco Solo's reply. It's deleted (for me). And the green light is a good point. Maybe because the curve starts to flatten, the volume of red/orange/yellow present is always a bigger mix than just green could provide to be seen as dominant.
@@martinleduc yeah it's weird that Marco's reply disappeared. The gist of his reply was that all light is scattered but blue/violet gets scattered more. when the sun is overhead, more blue light reaches the observer because it's scattered towards the observer from all over the sky. However, because of the low angle of the sun at sunrise and set, greater scattering of blue light means that more is scattered away than towards the observer.
Also, there is no "physics" color purple, as in a monochromatic frequency. It is a 'color sensation' caused by the cones in the eye receiving both red and blue light and how the brain processes it. In the CIE 1931 color diagram, it is a line drawn between red and blue and aptly named "the line of purples," the various shades being proportions of red and blue light mixed.
There is actually is monochromatic violet. "Red" cones are slightly sensitive to the shortest visible wavelengths, which is what allows us to perceive those wavelengths as violet. The same hue can be achieved with a mixture of blue and red light, as with other purples, although it would be slightly less saturated. Technically the line of pure purples extends between red and violet, not red and blue. Whether "violet" counts as "purple" is a semantic question, I suppose.
@@fwiffo This also leads to an interesting phenomenon. Taking a photograph of a violet flower can result in a blue image in a photograph. I have been somewhat surprised at a few flower photos when the film dries (I use slide film so you can see the positive image as soon as it dries).
Best explanation I've heard so far for this common question. Can you make a video answering a question from a 50-year old: "why the earth is flat?". It would be a good challenge for you :-)
what do you even mean by why? and how do you expect it to be answered? Would you like to be told it's because that's how God made it? There is no purpose behind it, there is no conscious decision behind why things are the way they are.
Fantastic video, just a couple of things which I think might be a little bit misleading 1. "Infrared is heat" - at everyday temperatures, sure. But all the rest of the spectrum for other temperatures. Including the sun's light. 2. "If you look at the sun, it's white" - At what time? At certain times of the day it can look yellow, orange or red. I mention this just because there is a common factoid that the sun is really white and therefore it's "wrong" to ever draw it as yellow. But of course, it looks yellow at least some of the time, and all drawings are based on how things appear to us, not their "true" color.
2. That's because you look through the atmosphere. If you were to look at the sun from space, you'd see that it is indeed white, with a very slight tint of green.
@@maythesciencebewithyou That's right, but I'm saying the statement "When you look at the sun, it's white" is at best misleading. When the sun is low enough in the sky to comfortably look at it, it's yellow.
Seems in some cultures the word for "blue" is "sky colored", and it is rarely used to describe other objects because so few other objects where "sky colored" before we had synthetic dyes - basically not many plants or animals are "sky colored", some rare ones are however red/blue - purple - because they strongly absorb green. I find it interesting some people can distinguish between violet and blue, but perceive it as similar somehow to "purple" (I do), perhaps to some "green cones not firing at all" effect in visual processing ?
When we say something IS blue, we usually means it absorbs all non-blue colours, and reflect the blue colours. That is not what is happening with the sky, it is not an object that is absorbing the non-blue and reflecting the blue. The distinction is a scientific one, in common language you probably sound pedantic if you don't simply say "the sky is blue" :-)
And to complement: why we find red sunsets so beautiful? Thats because of human psychology, as we are used to blue skies.. so red/orange being more rare makes it more appealing (if we saw it more.often red blue would be consideres a more beautiful sky 🤔)
One thing I don't understand from this explanation is the effect of Rayleigh scattering and involvement of actual atmospheric chemistry. Our atmosphere is at 79% N2 and ~20% O2, there is a balance of other gases but it has no effect to my question. I think it is such that this mixture of air (in a molecular view) small enough to propagate the Rayleigh scattering effect, and of course, as it propagates in the sky, the spectrum we perceive as blue would "further refine itself". What changes if we change the mixture composition though? How much oxygen would change the perceived spectrum response from scattering? Surely this must be a resolved question because we already study atmospheric gases coming from bodies in the solar system? Anyone know of a paper or book that discusses this basic idea?
I guess I found the answer after googling. It has to do with basically 1)electromagnetic scattering theory, and 2) the behavior of the molecule relative to the electromagnetic waves being propagated in regards to the sphere( mie solution). Things like bond distance , inherent molecular polarization vs simply put the "rearranging the expressions of energy(in terms of math) from electromagnetic waves relative to the geometry in which they have undergone their processing". Basically each variable in those turning points alludes to varying effects. Its pretty interesting to see the behavior at each limit. I'm also glad someone else decided to do this calculation so I can just read their hard work quickly lol.
On a totally different topic: how much matter would have been created by cosmos inflation which would have separated virtual particles that pop in and out of existence due to their quantum nature?
Good question. The answer is going to be that virtual particles are not actual particles, or some such nonsense. The real answer is beyond most physicists and worthy of a video for sure.
Why does air scatter blue light? I recall from George Gamov’s book “One, Two, Three, … Infinity!” that one needs to consider what happens in a cube of air 500nm (green wavelength) on a side. There is significant fluctuation on a fast (MHz) time scale of the distribution of air molecules in the cube, since there just aren’t that many molecules in it, and they are moving fast (the speed of sound). In even smaller cubes (blue wavelength) the fluctuations are even more pronounced and rapid. The density fluctuations correspond to fluctuations in the index of refraction, and the light you see has to pass through lots of these tiny cubes, so air scatters the light you see, and it scatters blue light more than green light, and green light more than red light.
"air scatters blue light more, so sky looks blue". "at sunset, light goes through more air so more air scatters blue light even more, so sky looks orange/red" scratching my head.
@@erikawanner7355 And you didn't notice that the explanation for the color blue of the sky in the beginning of the video (3:13) was that blue light is scattered more too? Why?
But doesn't it make more sense and less complicated to think that the OZONE layer which tends to have a pale blue color is being illuminated by the sun and, some of the blue light is being absorbed in that layer giving it a more blue color. Then as the angle of the sun traverses in it's orbit the blue gets deeper the less light there is. Also the reflection from the oceans bounces off like a mirror and give the whole planet a blue hue from space. isn't That why the sky is blue?
I would like to add that in the Greek times the name (by the existing literature) of the sky colour was purple (like a wine) and the same for the sea. Does that means our vision receptors changed? Or is something else as blue colour was the last one described (found) in the old texts?
Could possibly be vulcanic ash flying in the stratosphere scattering red light. Purple comes from mixing blue and red. I'm not sure if there were big eruptions in those days.
The hues associated with colour names have changed over time. For example, in Newton's "Opticks" the colour he calls blue is what we typically refer to as cyan today. What you mention is another example of that. It is not that our perception has changed, but rather that different words for various hues have shifted over centuries, just like many other types of words have.
Depends on the biology of their eye. And because water density in clouds is highest near the bottom and because the light scattered up from the top of the clouds can't make it down to the bottom of the clouds.
Watched it twice but something I'm not able to connect is that blue (and purple)light being scattered allows the sky to look blue, but with more air (sunsets) more blue light scattering makes the sky look red (?!)
Yep, there is clearly something missing from this explanation. Otherwise, nearly every sunrise and sunset would result in a fiery red sky, which is not even remotely the case. I believe the explanation for reddish-orange skies at these times is that other particulates in the air, such as smoke and dust, reflect red and orange wavelengths more, so when the light encounters lots of those things in the air, you get a nice fiery sunset.
I thought it was common knowledge that the oxygen and nitrogen in our atmosphere scatters more blue sunlight than any other color, but didn't know the full why until just now 🌞
“Air is blue” is NOT an incorrect answer. In general, the color of ANYTHING is defined by what wavelengths that thing reflects, refracts and absorbs. For a leaf, this adds up to green. For blood, it adds up to red. For sky, it adds up to blue And the explanation of HOW the sky is blue is the pretty much the same explanation of how anything else gets its color.
Thank you! Saying that the air around us isn't blue in answer to that is like telling an astronomer that star's aren't red when he just told you about redshift. You just need more sensitive equipment or enough of the stuff.
@@ZubairAhmed-yw5zg “Air is painted blue with a brush” is also an incorrect answer. Why are you investing intentionally and obviously wrong answer, just to say it’s wrong? You are the first one I hear saying the word “radiate blue”.
So why aren't photos of sky purple? Since RGB photodiodes inside a camera should have better 'vision' than human cone cells. Do manufacturers specifically design RGB diodes to be around the same sensitivity range as human vision?
Most LEDs are designed to be seen by humans, so the materials are picked such that they emit most of the light where human eyes are most sensitive. Thus it takes less power to give the same perceived brightness. The correspondence is not exact, there is also a drive towards using materials that are cheap and abundant, and easy to work with. Sidenote: When Akasaki got the Nobel prize for inventing the blue LED, a lot of people thought "What's the big deal, he simply invented one with a different colour?" But now we see how it has changed colour displays everywhere from the old cathode ray screens to flat ones that are portable and energy efficient.
I realize now that I answered a very different question than the one asked, apologies for not reading it correctly :) Digital cameras are built to portray the world as we humans see it, otherwise people wouldn't buy them because it doesn't look right. So they have filters in front of the sensor that emulate our vision. In science, astronomy for example, that is very different. They may use the same sensor types but without filters or with completely different ones. Typical colour sensor chips have what is called Bayer filters. For each 4 pixels there is 1 with red filter, 1 with blue filter and 2 with green filter. That is because our eyes are more sensitive to details in the green part of the spectrum. The photocell values are then combined into pixels using maths, either in hardware or software. When you shoot in RAW mode, the camera stores those individual values instead, typically also in a higher precision (dynamic range). Some people claim that their photo editor (often Adobe photoshop or lightroom) does a better job at the conversion than the software in the camera, especially when they adjust the process, but it is of course more work.
I'm not an expert in optics, but the basic idea is that the light internally reflects inside the water droplets, and returns at an angle of around 42 degrees. So if you look at the shadow of your own head (which is the shadow of where you're looking from, 0 degrees), the rainbow forms a circle 42 degrees away from that shadow. Double rainbows also exist, and these are when the light internally reflects inside the water droplets TWICE, so it comes in at a different angle. Wikipedia has some great images that help understand this: en.wikipedia.org/wiki/Rainbow I specifically like this one: en.wikipedia.org/wiki/Rainbow#/media/File:Rainbow_principle.svg
@@iveharzing _"...light internally reflects inside the water droplets, and returns at an angle of around 42 degrees."_ Which makes a circle from the perspective of the observer, if nothing is blocking the light like a big-ass planet sized rock they're standing on.
One thing I still want to know that... when we see anything how our eyes distinguish or find out where the light is coming from ...for. e.g here how does our eyes(or better to say brain) knows that the blue light is coming from sky and not directly from sun even thought all light rays are getting mixed and then entering into our eyes?
Starting with the easy part first: your brain knows where your eyes are pointed, so it does just come down to "how do our eyes know". Our eyes, or any camera or lense, gather light rays that are coming directly in. Any light that comes in from the side doesn't land on the retina and so isn't detected. If your lenses were also scattering light, that would be called cataracts, and you would have trouble seeing the world. Look up how a pin-hole camera works and you'll find a simple description of this.
air without clouds consists of oxygen and nitrogen. theses molecules are small compared to water molecules. small molecules interact much better with equally small wavelengths blue and purple. And this interaction means the small molecules absorb and re-emit the blue and purple light-photons in all directions but the red light passes straight through. That is "scattering" blue and blue purple. On the other hand water and dust are big molecules so they absorb and re-emit bigger wavelengths i.e. red light (sunset) or all the light (white clouds).
Thanks alot, after I see some Phd answer about tyndall effect, rayleigh and mie scattering, with confusion between tyndal effect and rayleigh, from this video both is same which have dependen on wavelength , it's same but because Lord Rayleigh publish it first so the blue sky caused by rayleigh scattering not tyndal effect.
I have a question. What if, insted of our eyes, we use a device that has the same sensitivity for all frequencies of visible light. What is de expected result ? The sum emits the same amout of photons for all colors ?
What human eye see is kind of average. We can not tell difference between single orange vs. yellow and red combined. Compare that to ear: 440 Hz and 880 Hz is a tone of music, not similar to a sound of 660 Hz wave. This was not said at all in the video.
Polarization of light is happening in a plane perpendicular to the direction of the light ray, like a piece of card board skewered on a sword. From the tip of the sword that means polarization can be in any angle, but seen straight from the side, it can only appear up-down. At angles between, there is still full up-down, but less of the sideways possible. In detail, a polarized photon absorbed by an electron will make the electron bounce up and down in the polarized direction (conservation of momentum). When another photon is emitted as the electron returns to the previous energy level, it can go in any direction, but will be polarized in the same direction the electron was bouncing. The bounce is not entirely literal, but the result is that 90 degrees from the Sun, you can only get scattered photons that are polarized in one direction, where closer or further (in degrees) from the Sun and further from it, you will get a mixture that increases towards even random distribution at 0 and 180 degrees from the Sun.
@@kimmium Yeah. I wish people would finally learn that everything we see is basically a culmination of physics. Even just one fundamental particle and its properties and effects and history and future and possibly even meaning to someone who stumbles on it and has some kind of beneficial connection to it that they are aware of at some point. All things we know and are are emergent properties of physics, some indirectly, but that doesn't make it _not_ an emergent property of physics. It's not just a thing to say; everything literally is physics.
I have a few questions. 1. How do scientists take measurements of the universe, using light that is not visible to us? You hear all the time stuff like, "using infrared, scientists measured blah blah blah", "using ultraviolet, scientists measured blah blah blah", and "using radio waves, scientists measured blah blah blah". 2. How did we discover that there was electromagnetic radiation outside the range of what humans can see, if by definition we can't see it? I can imagine that would not be easy. 3. How do we measure the wavelengths of electromagnetic radiation received from any given source? That is everything I can think of for now.
2. It was William Herschel that discovered infrared light. He wanted to investigate the spectrum of light from the Sun, so he set up a prism to split the light into a rainbow. His measurement method was to put sensitive thermometers in different parts of the spectrum to see how much energy was arriving of each colour. The story is that he coincidentally placed a thermometer outside the visible rainbow beyond the red end while setting up the experiment, and was surprised to notice that it registered an increase in temperature. Thus he concluded that parts of the spectrum from the Sun was not visible to us, yet clearly still present. 1. Later photosensitive emulsions were developed and photography was invented. Those emulsions were also sensitive to light outside the range that our eyes detect, and thus led to further experiments in the spectrum of the Sun and other light sources (candles, coal fire, etc). When the photo-electric effect was discovered, it became possible to create electric/electronic equipment that can measure much more accurately how much light falls on them. This eventually lead to the invention of CCD (Charge Coupled Device) chips, which were the fore runners of the digital cameras that are so common these days. 3. Light propagates as a wave, which can interfere with itself. So casting light from a narrow part of the spectrum onto two slits placed closely together, it can be calculated what the wave length is, based on the interference pattern formed on a screen (by varying the distance between the slits, and to the screen). The calculation is relatively straight forward, if you search a bit you are likely to find an explanation with details that is accessible from your skill level. Understanding of the spectrum and wavelengths made it possible to develop filters which only pass certain interesting wavelengths. This is often used in astronomy and satellite imagery, and allows satellites to tell the difference between dust clouds and rain clouds for example. So while we cannot see infrared and ultraviolet, we can still directly observe the effect on equipment such as thermometers, CCDs, photographic paper and many more. There is a lot more detail which you might find interesting, if you search around the web for a bit.
@@michaeldamolsen i understood bits and pieces of that. That is cool. Evidently, I have a lot of reading to do to further my understanding of this stuff.
@@alexandertownsend3291 What I find wonderful about reading science history is learning how they figured stuff out :) The history of understanding light spectra is particularly amazing, as it literally caused Planck to invent quantized energy levels, and Einstein showed how that could be used to explain the photo-electric effect, which launched all of quantum mechanics. Just wanted to warn you that it is a truly epic journey you might be embarking on :)
@@alexandertownsend3291 for the history of it see Cathy loves physics channel. Particularly James clerk maxwel. Fwiw your phone camera sees infrared and ultraviolet. It's just that they put red green blue mask over the sub pixels and slap an infrared filter over it so a picture looks similar to how a human eye would sense it. Real science sensors aren't blinded like that. Set your phone to take video and point your tv remote at it. You'll see the flashing ir led even thru a black plastic trash bag which is transparent in infrared. JWST specialises in infrared. The mirrors are gold plated as it works a bit better at those wavelengths.The further something is the more red shifted it is and you can see thru cosmic dust better in infrared. The light passes thru a grism (grating/prism) so where on the sensor it falls is determined by its wavelength. The spectrum tells you how fast it's moving and what it's made of. A prism also works at microwave frequencies of its made of paraphin instead of glass etc.
I'm wondering if we can go a little deeper into this subject of why the sky is blue. In viewing your color graph, I notice that light frequencies in the 500 nm range are depicted as blue. I think this is because when light of 500 nm frequency penetrates our eyes we see the color blue. But why blue? My first thought is that our eyes are sending a signal to our brains that our brains assign a value to that we sense as the color blue. That is, our brains are creating a visual representation of the world that manifests as color. So, is there really such a thing in reality as color or is color just our brain's reaction to a part of the energy spectrum as an evolutionary adaptation to promote survival? If the latter, then do different brains see different sky colors? How do I know that the blue in my brain is the same as the blue in your brain?
You're getting into the concept of qualia, which is something that applies to all types of perception. It can be existentially upsetting if you think about it too hard.
In reality there’s no color. As atom itself has no color. What you see is frequency value assigned color through evolution. We live in a sea of particles but we don’t experience that due to body.
The sky is not orange, that is simply light that reflects off clouds and dust particles in the air. The Sun no longer reaches you at the ground level, but can still shine on things higher up. On a very clear day, the sunset is very boring with not much color at all, except the Sun itself.
4:50 doesnt our eye lense also filter out violett light, that would be detectable by our blue cones? Also that what we percieve violett as color is actually a mix of blue and red, as we can't see true violett.
What we call “magenta” (not violet) is a mixture of blue and red light. Our eyes can detect violet, just not as well as blue. Violet light stimulates the green and red photoreceptors even less than blue light does, so are eyes can distinguish it from blue light.
Ultraviolet is not filtered out by the eye but it is mostly filtered out by most types of glass. As a result the retinas can be burnt by welding, even if its around a corner and reflected and we cannot detect it. Until our eyes get itchy and we spend a couple of days being blind, I guess you could call that detecting. Bottom line: No our eyes do not filter out violet and yes we can see it.
So, do some molecules in the atmosphere scatter light more than others? Is there one type of molecule that is predominantly responsible for the blueness?
And this is the next level deep of the question. If I remember right, I believe it is the oxygen and/or nitrogen in the air that reflects more of the blue light.
It is primarily the nitrogen molecules that are responsible for the scattering, but that is only because there is 5 times as much nitrogen as there is oxygen in the atmosphere. Their molecules are very similar in size (and shape of course, both being formed of 2 atoms limits the possible shapes), so if the atmosphere was simply oxygen the sky would look practically the same. Except there would be huge fires everywhere, so the soot and dust would have a very large impact :) Carbon dioxide and methane are different because the molecules are larger, they reflect more light in the infrared. Since Earth absorbs a lot of energy in visible light during daytime, and emits it again as infrared light at night, this is a bit of a problem. If Earth cannot get rid of all the heat it has accumulated, it will gradually warm up. I am not trying to push a climate agenda here, just mentioning the role scattering and reflection has on energy exchange.
The oxygen would cause stuff to rust. There is a lot of hydrogen around, so thats mostly what would be rusting. (Spoiler alert: It actually happened here on earth)
I Have question not related this topic but I think you can give me that answer The question is can we completely change particle into wave🤔 if yes how and if No then why not
I hope it was not intentional that you didn't even mention the scientist who specifically answered this question(why sky is blue? ) Sir CV raman, who later won the Nobel prize for his discovery of Raman effect.
So, if an alien see the earth, they might be bamboozled by us saying "little blue planet" But they might think that what we mean by blue is actually the color of ultraviolet
Funny, I thought everyone had fond memories of our mothers sitting us down and explaining the quartic scattering cross-section of nitrogen when we were toddlers :D (just joking here, in case that needed to be said)
Thanks for this video! I'd also be interested to learn why (at molecular level) blue light scatters more than other colors. And similarly why the sky on mars is reddish. -Kurt
To say that air molecules favorably scatter short-wavelength light, is just saying that air is blue. Blue paint is blue for the same reason. Blue pigment favorably scatters short-wavelength light. The reason that the sun matters is also for the same reason. You need light to see things. Neither the sky nor blue paint look blue without light. Air does not need to glow on its own to be blue any more than blue paint does. "Why is the sky blue" is not a more complicated question than "why is blue paint blue". They have the same answer. The follow-up question, "why does it favorably scatter short-wavelength light" might have a different answer. But changing the scattering mechanism doesn't change the color, if it doesn't change the spectrum of scattered light. "Why does that spectrum look blue" also has the same answer for both the sky, and for blue paint. Liquid oxygen is pale blue, and liquid ozone is blue-violet, and we don't treat their blueness as a special case. We shouldn't treat it as a special case when they're in the gas phase.
the explanations after 3:30 and 6:00 seem to contradict each other. Is the sky coloring the result of scattered light or non scattered light that reach us?
Blue light gets scattered away from the direction of the Sun, and can reach us from any direction after being scattered many times. This is why the sky looks blue in all directions. At sunrise and sunset the sky itself is still blue. What you see as spectacular sunrises/sets is the light that is NOT scattered, but instead reflected off clouds and dust. On a very clear day sunrises and sets are in fact very bland an boring. When the Sun is low in the sky, its light passes through more atmosphere, and even more scattering can occur. Thus, the Sun itself will appear to have lost the blue colours, and appear orange or red. In other words, if no light arrived to your eyes from an area of the sky which is not right next to the sun, it would appear black. The light that does arrive from the sky far from the Sun has gotten there by scattering. Blue light scatters more, which is why you see mostly blue light from those directions. At sunrise/sunset you are looking in the direction of the Sun (obviously). Thus you are not seeing all the light that is scattered, you see what is left, the light that did not scatter.
Early digital cameras DID have trouble with monochromatic violet. Example, violet plants appeared blue. For unknown reasons, it's rarely mentioned that the red cones in our eyes also have some sensitivity to wavelengths of around 380 nanometers (violet). So monochromatic violet light actually stimulates both blue AND red cones, otherwise we could never see monochromatic violet as a different color. In some early digital cameras, the red sensors had zero sensitivity to violet and could not faithfully reproduce that color. Anything violet would appear blue in the picture.
@@davethedaemon9024 What? So... if I understand this right, because of how our eyes work we _do_ see violet as purple? That is so weird. I was like, why is this guy calling violet purple when there's no red in it. But then purple still isn't a colour that exists in the world and no matter if we see violet or red and blue, we see a purple colour that exists only in our brains. Not that that's not weird XD It still annoys me that he says the sky _is_ blue. Next thing you know he tells us that because we're so low on the surface of this planet that the planet _is_ flat. Maybe to a photon coming towards it it physically is, but I'm pretty sure that relativity doesn't make a curved surface physically flat to massive objects on the surface, just as scattering doesn't alter the physical properties of the sky to make it blue.
No it isn't because there's nothing in physics that can convey what our experience of blue is to someone who's never seen blue before. You can say it's 500 nm light but they still won't know
Given that a lot of ancient literature refers to "wine dark seas" could it be that 2000 years ago humans had a violet detecting cone that we have since lost?
There was a hypothesis that the water commonly used to water down wine in those days might be alkaline due to limestone content, it might change the hue of the wine towards the blueish. However, it is more widely believed that it is simply a poetic expression, perhaps referring more to the darkness rather than the hue. While trying to find references on this, I came across a delightful New York Times article from 1983 of the title "Homer's Sea: Dark Wine?" you should find it easily by searching for that :-)
Also noticed that (according to the graph in the video) the Sun's output in violet is significantly less than its output in blue -- if we were on a planet orbiting in the habitable zone of a class B star, the sky might indeed have a shade of violet in it (although the lesser but still significant scattering of green light would keep the color from being totally in the short wavelength range, as it does on Earth).
No stars can be violet this happens because the peak is in ultraviolet/violet, but a large about of the other colors is emited making the star look whitish-blue
@@HugoFilho. A very hot star wouldn't appear violet (unless viewed through a really weird atmosphere), but the sky could appear violet from scattering the light of a very hot star.
If I asked an adult why the sky is blue and they answered: "Because the ocean is blue it reflects the light from the sun....": I don't think I would ask them any more questions.
Indeed. Anybody who has been to the beach knows that seawater is colorless.
Because god erased the rainbow and is colour blind and forgot the blue, otherwise it'd be dark all day.
If it was up to me I'd not ask anyone anything.
Look, I know a scientist, super smart guy, he says the sky is blue on a sunny day. He says it's red sometimes in the evening. And it should be purple, but we have trouble seeing violet, which isn't purple and the sky has no colour and purple isn't a colour but two and brains make us see things, not eyes, otherwise you'd be seeing red and blue.
I understand that about half of the US is creationist or worse and has the mental capacity of a toddler, but I can assure you, there are grown ups in the world, some even in America.
The sun doesn't rise or set, the planet rotates. What you observe isn't necessarily what the thing actually is. Next thing you know Fermilab is making videos of how the Earth is flat from up close and it changes shape if you go up high enough.
Obviously the sky is blue because they ran out of red paint.
When I taught at a university I asked that question to every class, and only once didn't get the ocean answer.
The water is the one that reflects. There are forest pools, where the water may be green, brown or almost black, because there is not much sky to reflect. Those other colors are usually far darker than the sky blue. Agaist a brick wall you may find even red water.
Could you please make a video on "Why scattering occurs?"
Finally more Don Lincoln good physics content
Congrats for explaining such a common topic and making it sound so simple.
Love all your submissions, Simply put - You are the best at explaining everything from Quantum Mechanics to the scattering of sunlight😀
scattering of sunlight IS quantummechanics😃
@@misterphmpg8106 yeah but he named only Newtonian physicists so... it doesn't count.
For once - I kinda knew this … I’m excited for new uploads. I wish you had a ton of Fermi paradox ones.
Stephen Hawking said something similar: he liked hearing what children asked because they didn't know enough NOT to ask the big questions.
Kids are natural philosophers too. As a small kid I was always wondering things like "Why am I real", and "What is nothingness". Things that vex philosophers , and physicsts , to this day. Not that I had an answer, but yeah.
@@shayneoneill1506 Absolutely. Children's minds tend to be open, it's only as adults (as Einstein noted) that we develop the set of prejudices we call 'common sense'.
Isn't it weird how adults are meant to know enough to not ask the questions that could very well provide the answers we were searching for all along... Backward at coming forward, or so the saying goes.
@@_34_Lies Yep. I think it's partly because as adults, we're given to think that imagination is a bad thing, thinking differently is bad, and questioning accepted axioms is foolish. Fortunately, those rare individuals who make the big breakthroughs never lose that childlike wonder that lets them see further, differently, or something that is hidden from the rest of us.
@@Nigelrudyardmusic hopefully, it's not beyond our reach. If we can develop and nurture the courage to ask the right questions, so much more may be available.
Good video explaining the colors in the sky...but that cute little girl near the end of the video!
I've heard this before, so I listened to see if anything had changed. The biggest change was that the human eye is imperfect at seeing the purple spectrum of light.
I was expecting Dr. Lincoln to just walk off the screen with the VERY first explanation. and walk back on from the other side to finish the video!
Excellent, Don! This is the sort of thing I used to head down to the local library to find out in the late 1950s and 1960s. No Internet! When I got my first digital camera around 2002 and had to work out how to stop blue skies going purple. Now I know just why they went purple. Thanks!
You should do more of these 'childhood-type' question videos if only to remind us where we came from. One of my earliest memories of working something out was realising aged two or three that wind wasn't caused by the trees waving around.
Same here for me but in the 1990s right before the internet came out. Having been born at he end of the 1980s, I’m the last generation to have known what it’s like to have had to rely on the library for all the answers to questions no one you knew could give you lol.
Wow, I was thinking "maybe digital cameras see the sky purple, but photos on my camera are blue, maybe it's a software correction",
now I know some cameras really used to "see" purple, good to know that, thanks for sharing.
some of my earliest memories are of visiting fermi lab (my dad worked there)... floor 15 makes an impression. just found the channel today, but it seems like floor 15 is on youtube now (i mean, has been. the algorithm really failed me this time)... anyway, peter, i too vote for more "childhood-type" questions
My gosh, I told my daughter it was because of Rayleigh scattering. I was sweating a bit during this video but turns out I didn't misguide too much.
...now I'd like to see how you explained Rayleigh Scattering to your daughter (I'm assuming, as your post was a day ago, that you are still explaining that part😉)
@@markzambelli I would say "air is made out small things and light is a bunch of small waves; the smallest waves bounce the most and spread out for us to see"
I love children's curiosity and new ideas!
I must say that that was quite an illuminating video Dr. Don! 👍👍😉😉 Good to see you back!
Off topic but I keep looking for your ‘stache. Thanks for sharing your knowledge, I appreciate you Dr Don
i think I got the sunset thing, but it is quite confusing at first (scattering blue light makes a blue sky, except for sunset, then scattering even more blue light makes the sky orange. what?). If you can see a picture from space, it helps. The blue being scattered means it can't penetrate as deep, as it goes in all kinds if directions rather than away from the sun.
at the low angle in the morning and in the evening, the light has to pass through more atmosphere. The light always scatters randomly in all directions. When it reaches you, most of the blue light has already scattered away from you. When the sun is higher, the light doesn't have to travel much to reach your eye. More scattered blue light reaches your eye.
Night stars appear then disappear
Sun appears domineers our sphere
Reflective light of day does appear
Blue sky molecules in atmosphere
No other planet so lucky is near
Thanks Doctor Lincoln. I remeber from school that critical opalesence was mentioned but cannot remeber what it is and if it plays a role here. I am sure you know. Keep up the good work
Raleigh is a really good argument for nominative determinism
Excellent. I'll make my grandkids watch this instead of mis-explaining it. Thanks!
I LOVE THIS CHANNEL
Thanks Dr. L!!!
Fun fact, the sky is *not* blue, it is cyan. What you call "indigo" in the video is the actual color blue. Cyan sits somewhere between blue and green. The arrows at 3:37 should therefore read "red, orange, green, cyan, blue and violet".
I really enjoy this channel!
THANK YOU PROFESSOR LINCOLN...!!!
There was one detail that slipped through. During those spectacular sunsets, what looks red-orange is the light reflected from the clouds and the sun itself. But the actual sky still looks blue.
You can see it at 6:21.
Actually the red, orange and yellow colors appear in the clouds before they appear in the sky. If you pay close attention to the sky after sunset on a clear day the sky will glow yellow, orange and red before the darkness settles in.
There is a flash of green too, but its a secret. Dr. Becky showed the internet, but nobody else knows about it.
Great just want more
Sir this is a very informative videos. Please make a video on conservation of momentum (field +particle momentum) in classical electrodynamics.
I always feel there's a step missing in the explanation of Rayleigh scattering. If blue (and violet) light is being scattered more, then wouldn't it be scattered away from the observer? This would suggest that the sky should always be orange/red not just at sunrise and sunset.
I've never found a decent explanation to fill in that gap between blue light scattering and more blue light reaching the observer.
@@marcosolo6491 thanks Marco, I assumed that if I posted the question someone would eventually reply🙂
@@marcosolo6491 very good explanation. But it also begs the question, why no green?
I think you have to think of it as being scattered toward you and not being scattered away from you. Because if the other colors just go straight down while blue is coming to you from all directions because of the scattering, then naturally you're gonna see more blue than the other colors, but only if the medium is short enough. If the medium is getting longer then you start having less and less blue light left to be scattered around and the other colors overtake.
But I might be wrong, please restate Marco Solo's reply. It's deleted (for me).
And the green light is a good point. Maybe because the curve starts to flatten, the volume of red/orange/yellow present is always a bigger mix than just green could provide to be seen as dominant.
@@amalieemmynoether992 If you can, could you please rewrite in your words the answer from Marco? It seems to have been deleted.
@@martinleduc yeah it's weird that Marco's reply disappeared. The gist of his reply was that all light is scattered but blue/violet gets scattered more. when the sun is overhead, more blue light reaches the observer because it's scattered towards the observer from all over the sky. However, because of the low angle of the sun at sunrise and set, greater scattering of blue light means that more is scattered away than towards the observer.
4:18 “squishy biology stuff” heh nice poke there, I wonder what biologists say about physics?
Also, there is no "physics" color purple, as in a monochromatic frequency. It is a 'color sensation' caused by the cones in the eye receiving both red and blue light and how the brain processes it. In the CIE 1931 color diagram, it is a line drawn between red and blue and aptly named "the line of purples," the various shades being proportions of red and blue light mixed.
There is actually is monochromatic violet. "Red" cones are slightly sensitive to the shortest visible wavelengths, which is what allows us to perceive those wavelengths as violet.
The same hue can be achieved with a mixture of blue and red light, as with other purples, although it would be slightly less saturated. Technically the line of pure purples extends between red and violet, not red and blue.
Whether "violet" counts as "purple" is a semantic question, I suppose.
@@fwiffo This also leads to an interesting phenomenon. Taking a photograph of a violet flower can result in a blue image in a photograph. I have been somewhat surprised at a few flower photos when the film dries (I use slide film so you can see the positive image as soon as it dries).
Best explanation I've heard so far for this common question. Can you make a video answering a question from a 50-year old: "why the earth is flat?". It would be a good challenge for you :-)
It's nearly impossible to convince religious people ....
My Physics teacher use to say, we only explain "how" not "why". This is How the sky is blue, not why.
what do you even mean by why? and how do you expect it to be answered? Would you like to be told it's because that's how God made it? There is no purpose behind it, there is no conscious decision behind why things are the way they are.
Fantastic video, just a couple of things which I think might be a little bit misleading
1. "Infrared is heat" - at everyday temperatures, sure. But all the rest of the spectrum for other temperatures. Including the sun's light.
2. "If you look at the sun, it's white" - At what time? At certain times of the day it can look yellow, orange or red. I mention this just because there is a common factoid that the sun is really white and therefore it's "wrong" to ever draw it as yellow. But of course, it looks yellow at least some of the time, and all drawings are based on how things appear to us, not their "true" color.
2. That's because you look through the atmosphere. If you were to look at the sun from space, you'd see that it is indeed white, with a very slight tint of green.
@@maythesciencebewithyou That's right, but I'm saying the statement "When you look at the sun, it's white" is at best misleading. When the sun is low enough in the sky to comfortably look at it, it's yellow.
Seems in some cultures the word for "blue" is "sky colored", and it is rarely used to describe other objects because so few other objects where "sky colored" before we had synthetic dyes - basically not many plants or animals are "sky colored", some rare ones are however red/blue - purple - because they strongly absorb green. I find it interesting some people can distinguish between violet and blue, but perceive it as similar somehow to "purple" (I do), perhaps to some "green cones not firing at all" effect in visual processing ?
Please make a video on what exactly charge is, from where does it come!!
Dr. Lincoln, has anyone asked you were you get those snappy t-shirts? Great videos!
It totally makes sense that my cat would see the sky as purple with fluffy clouds.
"The sky looks blue when you shine white light through them" sounds an awful lot like "the sky is blue". What is the difference?
When we say something IS blue, we usually means it absorbs all non-blue colours, and reflect the blue colours. That is not what is happening with the sky, it is not an object that is absorbing the non-blue and reflecting the blue. The distinction is a scientific one, in common language you probably sound pedantic if you don't simply say "the sky is blue" :-)
I love your videos thank you Mister 😊
And to complement: why we find red sunsets so beautiful? Thats because of human psychology, as we are used to blue skies.. so red/orange being more rare makes it more appealing (if we saw it more.often red blue would be consideres a more beautiful sky 🤔)
I think so! You are so amazing! Thank you to watch with me! I love you so much!
@@VikaShaparnaya my pleasure to watch ur eyes changing colors while we watch the sky (internal joke) 😍
"Every child is born an artist. The trouble is keeping them that way." --Pablo Picasso
One thing I don't understand from this explanation is the effect of Rayleigh scattering and involvement of actual atmospheric chemistry. Our atmosphere is at 79% N2 and ~20% O2, there is a balance of other gases but it has no effect to my question. I think it is such that this mixture of air (in a molecular view) small enough to propagate the Rayleigh scattering effect, and of course, as it propagates in the sky, the spectrum we perceive as blue would "further refine itself". What changes if we change the mixture composition though? How much oxygen would change the perceived spectrum response from scattering? Surely this must be a resolved question because we already study atmospheric gases coming from bodies in the solar system? Anyone know of a paper or book that discusses this basic idea?
I guess I found the answer after googling. It has to do with basically 1)electromagnetic scattering theory, and 2) the behavior of the molecule relative to the electromagnetic waves being propagated in regards to the sphere( mie solution). Things like bond distance , inherent molecular polarization vs simply put the "rearranging the expressions of energy(in terms of math) from electromagnetic waves relative to the geometry in which they have undergone their processing". Basically each variable in those turning points alludes to varying effects. Its pretty interesting to see the behavior at each limit. I'm also glad someone else decided to do this calculation so I can just read their hard work quickly lol.
How come cameras also see blue instead of purple?
I came for the t-shirt, stay for the topic
Wow, that WAS AMAZING!
You should have explained why air scatters blue light the most.
Why do air molecules scatter blue light?
I'm not a scientist but i suspect it has something to do with the length of the wavelength.
On a totally different topic: how much matter would have been created by cosmos inflation which would have separated virtual particles that pop in and out of existence due to their quantum nature?
Good question. The answer is going to be that virtual particles are not actual particles, or some such nonsense. The real answer is beyond most physicists and worthy of a video for sure.
Thank you great explanation 🙂
Why does air scatter blue light?
I recall from George Gamov’s book “One, Two, Three, … Infinity!” that one needs to consider what happens in a cube of air 500nm (green wavelength) on a side. There is significant fluctuation on a fast (MHz) time scale of the distribution of air molecules in the cube, since there just aren’t that many molecules in it, and they are moving fast (the speed of sound). In even smaller cubes (blue wavelength) the fluctuations are even more pronounced and rapid.
The density fluctuations correspond to fluctuations in the index of refraction, and the light you see has to pass through lots of these tiny cubes, so air scatters the light you see, and it scatters blue light more than green light, and green light more than red light.
I learned something!
Great video, doc. May I pose a question? Are there any animals living whose eyes are such that the sky would appear violet? Thank you.
Sure. There are even ones that see ultraviolet. Google it.
I've heard that the sky appears violet to owls
@@kruthikaamar3244 Thanks. I'll take a look.
@@drdon5205 incredible; that would be something to see.
His answer is an answer of genius while your question is a question of more genius.
Cameras must have the blue bias also, otherwise photos would look weird.
"air scatters blue light more, so sky looks blue".
"at sunset, light goes through more air so more air scatters blue light even more, so sky looks orange/red"
scratching my head.
So, if the sunset is red because of major scattering of shorter wavelengths of light - then the explanation doesn't really compute.
That was just explained towards the end of his video… blue light is scattered more because of how low the sun is in the sky.
@@erikawanner7355
And you didn't notice that the explanation for the color blue of the sky in the beginning of the video (3:13) was that blue light is scattered more too? Why?
"Wait, is the sky really purple?"
Well, when I get a purple haze in my brain I do need to be excused while I kiss the sky. Make of that what you will.
The video also reminded me of Jimi and this great song.
Turns out he really was onto something... other than acid 😅
I resent being called a toddler cos I asked this question: I'm turning 40 this year! LOL! Great video :)
But doesn't it make more sense and less complicated to think that the OZONE layer which tends to have a pale blue color is being illuminated by the sun and, some of the blue light is being absorbed in that layer giving it a more blue color. Then as the angle of the sun traverses in it's orbit the blue gets deeper the less light there is. Also the reflection from the oceans bounces off like a mirror and give the whole planet a blue hue from space. isn't That why the sky is blue?
Omg I died at 0:02
I would like to add that in the Greek times the name (by the existing literature) of the sky colour was purple (like a wine) and the same for the sea. Does that means our vision receptors changed? Or is something else as blue colour was the last one described (found) in the old texts?
Could possibly be vulcanic ash flying in the stratosphere scattering red light. Purple comes from mixing blue and red. I'm not sure if there were big eruptions in those days.
The hues associated with colour names have changed over time. For example, in Newton's "Opticks" the colour he calls blue is what we typically refer to as cyan today. What you mention is another example of that. It is not that our perception has changed, but rather that different words for various hues have shifted over centuries, just like many other types of words have.
My guy video record the sky with your phone.. what do you see? Blue ? It’s because god made it blue
This might be a little esoteric, Prof... but what are your thoughts about the Koide formula for particle masses? 😁
Do any animals see purple skies then?
And also do dark clouds look white from above?
Depends on the biology of their eye. And because water density in clouds is highest near the bottom and because the light scattered up from the top of the clouds can't make it down to the bottom of the clouds.
Yooooooo mind blown! Thank you
Watched it twice but something I'm not able to connect is that blue (and purple)light being scattered allows the sky to look blue, but with more air (sunsets) more blue light scattering makes the sky look red (?!)
Yep, there is clearly something missing from this explanation. Otherwise, nearly every sunrise and sunset would result in a fiery red sky, which is not even remotely the case. I believe the explanation for reddish-orange skies at these times is that other particulates in the air, such as smoke and dust, reflect red and orange wavelengths more, so when the light encounters lots of those things in the air, you get a nice fiery sunset.
Yes, I came here to say the same thing! I watched the video twice in case I missed something the first time, but I didn't.
I think the reddish sunset because red wavelength also scattered so it appear red.
6
I thought it was common knowledge that the oxygen and nitrogen in our atmosphere scatters more blue sunlight than any other color, but didn't know the full why until just now 🌞
“Air is blue” is NOT an incorrect answer.
In general, the color of ANYTHING is defined by what wavelengths that thing reflects, refracts and absorbs. For a leaf, this adds up to green. For blood, it adds up to red. For sky, it adds up to blue
And the explanation of HOW the sky is blue is the pretty much the same explanation of how anything else gets its color.
Thank you!
Saying that the air around us isn't blue in answer to that is like telling an astronomer that star's aren't red when he just told you about redshift. You just need more sensitive equipment or enough of the stuff.
'Air radiates blue ' is an incorrect answer
@@bjorntantau194 ahahah
@@ZubairAhmed-yw5zg “Air is painted blue with a brush” is also an incorrect answer.
Why are you investing intentionally and obviously wrong answer, just to say it’s wrong? You are the first one I hear saying the word “radiate blue”.
@@juzoli i thought I was right when he said about air in the dark, and clearly it isn't blue then
Would you tell how am I wrong?
All in metric, giving a like, and a comment. :D
In England, where I live, kids ask ‘why is the sky grey?’
So why aren't photos of sky purple? Since RGB photodiodes inside a camera should have better 'vision' than human cone cells. Do manufacturers specifically design RGB diodes to be around the same sensitivity range as human vision?
Most LEDs are designed to be seen by humans, so the materials are picked such that they emit most of the light where human eyes are most sensitive. Thus it takes less power to give the same perceived brightness. The correspondence is not exact, there is also a drive towards using materials that are cheap and abundant, and easy to work with.
Sidenote: When Akasaki got the Nobel prize for inventing the blue LED, a lot of people thought "What's the big deal, he simply invented one with a different colour?" But now we see how it has changed colour displays everywhere from the old cathode ray screens to flat ones that are portable and energy efficient.
I realize now that I answered a very different question than the one asked, apologies for not reading it correctly :)
Digital cameras are built to portray the world as we humans see it, otherwise people wouldn't buy them because it doesn't look right. So they have filters in front of the sensor that emulate our vision. In science, astronomy for example, that is very different. They may use the same sensor types but without filters or with completely different ones.
Typical colour sensor chips have what is called Bayer filters. For each 4 pixels there is 1 with red filter, 1 with blue filter and 2 with green filter. That is because our eyes are more sensitive to details in the green part of the spectrum. The photocell values are then combined into pixels using maths, either in hardware or software.
When you shoot in RAW mode, the camera stores those individual values instead, typically also in a higher precision (dynamic range). Some people claim that their photo editor (often Adobe photoshop or lightroom) does a better job at the conversion than the software in the camera, especially when they adjust the process, but it is of course more work.
A detail explanation about the rainbow would be nice. Why we see one rainbow and not many and why it is circular?
I'm not an expert in optics, but the basic idea is that the light internally reflects inside the water droplets, and returns at an angle of around 42 degrees. So if you look at the shadow of your own head (which is the shadow of where you're looking from, 0 degrees), the rainbow forms a circle 42 degrees away from that shadow.
Double rainbows also exist, and these are when the light internally reflects inside the water droplets TWICE, so it comes in at a different angle.
Wikipedia has some great images that help understand this: en.wikipedia.org/wiki/Rainbow
I specifically like this one: en.wikipedia.org/wiki/Rainbow#/media/File:Rainbow_principle.svg
@@iveharzing _"...light internally reflects inside the water droplets, and returns at an angle of around 42 degrees."_
Which makes a circle from the perspective of the observer, if nothing is blocking the light like a big-ass planet sized rock they're standing on.
One thing I still want to know that... when we see anything how our eyes distinguish or find out where the light is coming from ...for. e.g here how does our eyes(or better to say brain) knows that the blue light is coming from sky and not directly from sun even thought all light rays are getting mixed and then entering into our eyes?
Starting with the easy part first: your brain knows where your eyes are pointed, so it does just come down to "how do our eyes know". Our eyes, or any camera or lense, gather light rays that are coming directly in. Any light that comes in from the side doesn't land on the retina and so isn't detected. If your lenses were also scattering light, that would be called cataracts, and you would have trouble seeing the world. Look up how a pin-hole camera works and you'll find a simple description of this.
Why shorter wavelengths are scattered more than longer ones by air molecules? What's happening?
Great explanation. But why does the air scatter blue more than red?
There is a great science asylum episode about this. Tl;dr it involves quantum physics
air without clouds consists of oxygen and nitrogen. theses molecules are small compared to water molecules. small molecules interact much better with equally small wavelengths blue and purple. And this interaction means the small molecules absorb and re-emit the blue and purple light-photons in all directions but the red light passes straight through. That is "scattering" blue and blue purple. On the other hand water and dust are big molecules so they absorb and re-emit bigger wavelengths i.e. red light (sunset) or all the light (white clouds).
Thanks alot, after I see some Phd answer about tyndall effect, rayleigh and mie scattering, with confusion between tyndal effect and rayleigh, from this video both is same which have dependen on wavelength , it's same but because Lord Rayleigh publish it first so the blue sky caused by rayleigh scattering not tyndal effect.
The Tyndall effect is when you have particulate matter (thin dust) scattering the light, whereas the Rayleigh scattering is a molecular phenomenon.
I have a question. What if, insted of our eyes, we use a device that has the same sensitivity for all frequencies of visible light. What is de expected result ?
The sum emits the same amout of photons for all colors ?
What human eye see is kind of average. We can not tell difference between single orange vs. yellow and red combined. Compare that to ear: 440 Hz and 880 Hz is a tone of music, not similar to a sound of 660 Hz wave. This was not said at all in the video.
Why is it polarized?
Polarization of light is happening in a plane perpendicular to the direction of the light ray, like a piece of card board skewered on a sword. From the tip of the sword that means polarization can be in any angle, but seen straight from the side, it can only appear up-down. At angles between, there is still full up-down, but less of the sideways possible.
In detail, a polarized photon absorbed by an electron will make the electron bounce up and down in the polarized direction (conservation of momentum). When another photon is emitted as the electron returns to the previous energy level, it can go in any direction, but will be polarized in the same direction the electron was bouncing. The bounce is not entirely literal, but the result is that 90 degrees from the Sun, you can only get scattered photons that are polarized in one direction, where closer or further (in degrees) from the Sun and further from it, you will get a mixture that increases towards even random distribution at 0 and 180 degrees from the Sun.
Physics, and Biology, are everything
Life, the culmination of physics
@@kimmium Yeah. I wish people would finally learn that everything we see is basically a culmination of physics. Even just one fundamental particle and its properties and effects and history and future and possibly even meaning to someone who stumbles on it and has some kind of beneficial connection to it that they are aware of at some point. All things we know and are are emergent properties of physics, some indirectly, but that doesn't make it _not_ an emergent property of physics.
It's not just a thing to say; everything literally is physics.
I have a few questions.
1. How do scientists take measurements of the universe, using light that is not visible to us? You hear all the time stuff like, "using infrared, scientists measured blah blah blah", "using ultraviolet, scientists measured blah blah blah", and "using radio waves, scientists measured blah blah blah".
2. How did we discover that there was electromagnetic radiation outside the range of what humans can see, if by definition we can't see it? I can imagine that would not be easy.
3. How do we measure the wavelengths of electromagnetic radiation received from any given source?
That is everything I can think of for now.
2. It was William Herschel that discovered infrared light. He wanted to investigate the spectrum of light from the Sun, so he set up a prism to split the light into a rainbow. His measurement method was to put sensitive thermometers in different parts of the spectrum to see how much energy was arriving of each colour. The story is that he coincidentally placed a thermometer outside the visible rainbow beyond the red end while setting up the experiment, and was surprised to notice that it registered an increase in temperature. Thus he concluded that parts of the spectrum from the Sun was not visible to us, yet clearly still present.
1. Later photosensitive emulsions were developed and photography was invented. Those emulsions were also sensitive to light outside the range that our eyes detect, and thus led to further experiments in the spectrum of the Sun and other light sources (candles, coal fire, etc). When the photo-electric effect was discovered, it became possible to create electric/electronic equipment that can measure much more accurately how much light falls on them. This eventually lead to the invention of CCD (Charge Coupled Device) chips, which were the fore runners of the digital cameras that are so common these days.
3. Light propagates as a wave, which can interfere with itself. So casting light from a narrow part of the spectrum onto two slits placed closely together, it can be calculated what the wave length is, based on the interference pattern formed on a screen (by varying the distance between the slits, and to the screen). The calculation is relatively straight forward, if you search a bit you are likely to find an explanation with details that is accessible from your skill level. Understanding of the spectrum and wavelengths made it possible to develop filters which only pass certain interesting wavelengths. This is often used in astronomy and satellite imagery, and allows satellites to tell the difference between dust clouds and rain clouds for example.
So while we cannot see infrared and ultraviolet, we can still directly observe the effect on equipment such as thermometers, CCDs, photographic paper and many more. There is a lot more detail which you might find interesting, if you search around the web for a bit.
@@michaeldamolsen i understood bits and pieces of that. That is cool. Evidently, I have a lot of reading to do to further my understanding of this stuff.
@@alexandertownsend3291 What I find wonderful about reading science history is learning how they figured stuff out :)
The history of understanding light spectra is particularly amazing, as it literally caused Planck to invent quantized energy levels, and Einstein showed how that could be used to explain the photo-electric effect, which launched all of quantum mechanics. Just wanted to warn you that it is a truly epic journey you might be embarking on :)
invisible light is easily detectable by your a*se, you can see it through your a*s, that's why all astrophysicists have all such huge a*ses
@@alexandertownsend3291 for the history of it see Cathy loves physics channel. Particularly James clerk maxwel. Fwiw your phone camera sees infrared and ultraviolet. It's just that they put red green blue mask over the sub pixels and slap an infrared filter over it so a picture looks similar to how a human eye would sense it. Real science sensors aren't blinded like that. Set your phone to take video and point your tv remote at it. You'll see the flashing ir led even thru a black plastic trash bag which is transparent in infrared.
JWST specialises in infrared. The mirrors are gold plated as it works a bit better at those wavelengths.The further something is the more red shifted it is and you can see thru cosmic dust better in infrared. The light passes thru a grism (grating/prism) so where on the sensor it falls is determined by its wavelength. The spectrum tells you how fast it's moving and what it's made of. A prism also works at microwave frequencies of its made of paraphin instead of glass etc.
I'm wondering if we can go a little deeper into this subject of why the sky is blue. In viewing your color graph, I notice that light frequencies in the 500 nm range are depicted as blue. I think this is because when light of 500 nm frequency penetrates our eyes we see the color blue. But why blue? My first thought is that our eyes are sending a signal to our brains that our brains assign a value to that we sense as the color blue. That is, our brains are creating a visual representation of the world that manifests as color. So, is there really such a thing in reality as color or is color just our brain's reaction to a part of the energy spectrum as an evolutionary adaptation to promote survival? If the latter, then do different brains see different sky colors? How do I know that the blue in my brain is the same as the blue in your brain?
You're getting into the concept of qualia, which is something that applies to all types of perception.
It can be existentially upsetting if you think about it too hard.
In reality there’s no color. As atom itself has no color. What you see is frequency value assigned color through evolution. We live in a sea of particles but we don’t experience that due to body.
Following question is something like: After sunset, the sky comes to blue again beofre it darkens. Why isn't the sky orange all the way till night?
The sky is not orange, that is simply light that reflects off clouds and dust particles in the air. The Sun no longer reaches you at the ground level, but can still shine on things higher up. On a very clear day, the sunset is very boring with not much color at all, except the Sun itself.
4:50 doesnt our eye lense also filter out violett light, that would be detectable by our blue cones? Also that what we percieve violett as color is actually a mix of blue and red, as we can't see true violett.
What we call “magenta” (not violet) is a mixture of blue and red light. Our eyes can detect violet, just not as well as blue. Violet light stimulates the green and red photoreceptors even less than blue light does, so are eyes can distinguish it from blue light.
Ultraviolet is not filtered out by the eye but it is mostly filtered out by most types of glass. As a result the retinas can be burnt by welding, even if its around a corner and reflected and we cannot detect it. Until our eyes get itchy and we spend a couple of days being blind, I guess you could call that detecting.
Bottom line: No our eyes do not filter out violet and yes we can see it.
And what is Rayleigh scattering?
also, when you say air molecules, does that mean mostly nitrogen molecules? Thanks.
So, do some molecules in the atmosphere scatter light more than others? Is there one type of molecule that is predominantly responsible for the blueness?
And this is the next level deep of the question. If I remember right, I believe it is the oxygen and/or nitrogen in the air that reflects more of the blue light.
It is primarily the nitrogen molecules that are responsible for the scattering, but that is only because there is 5 times as much nitrogen as there is oxygen in the atmosphere. Their molecules are very similar in size (and shape of course, both being formed of 2 atoms limits the possible shapes), so if the atmosphere was simply oxygen the sky would look practically the same. Except there would be huge fires everywhere, so the soot and dust would have a very large impact :)
Carbon dioxide and methane are different because the molecules are larger, they reflect more light in the infrared. Since Earth absorbs a lot of energy in visible light during daytime, and emits it again as infrared light at night, this is a bit of a problem. If Earth cannot get rid of all the heat it has accumulated, it will gradually warm up. I am not trying to push a climate agenda here, just mentioning the role scattering and reflection has on energy exchange.
The oxygen would cause stuff to rust. There is a lot of hydrogen around, so thats mostly what would be rusting. (Spoiler alert: It actually happened here on earth)
I Have question not related this topic but I think you can give me that answer
The question is can we completely change particle into wave🤔 if yes how and if No then why not
thx a lot
how did you know something is some color, and who told you to select the interpretation of the labels, colors
I hope it was not intentional that you didn't even mention the scientist who specifically answered this question(why sky is blue? ) Sir CV raman, who later won the Nobel prize for his discovery of Raman effect.
So the atmosphere is one giant prism?
So, if an alien see the earth, they might be bamboozled by us saying "little blue planet"
But they might think that what we mean by blue is actually the color of ultraviolet
Yeah, I have tried explaining this to a 3 year old, it's not so simple for them to understand.
Funny, I thought everyone had fond memories of our mothers sitting us down and explaining the quartic scattering cross-section of nitrogen when we were toddlers :D
(just joking here, in case that needed to be said)
@@michaeldamolsen your kids parties must have been amazing, haha!!
I’m confident I can outsmart a 2 year old… but, I still am uncertain if I’m “Smarter Than A 5th Grader” and that sucks!
Thanks for this video!
I'd also be interested to learn why (at molecular level) blue light scatters more than other colors. And similarly why the sky on mars is reddish.
-Kurt
To say that air molecules favorably scatter short-wavelength light, is just saying that air is blue. Blue paint is blue for the same reason. Blue pigment favorably scatters short-wavelength light.
The reason that the sun matters is also for the same reason. You need light to see things. Neither the sky nor blue paint look blue without light. Air does not need to glow on its own to be blue any more than blue paint does.
"Why is the sky blue" is not a more complicated question than "why is blue paint blue". They have the same answer.
The follow-up question, "why does it favorably scatter short-wavelength light" might have a different answer. But changing the scattering mechanism doesn't change the color, if it doesn't change the spectrum of scattered light.
"Why does that spectrum look blue" also has the same answer for both the sky, and for blue paint.
Liquid oxygen is pale blue, and liquid ozone is blue-violet, and we don't treat their blueness as a special case. We shouldn't treat it as a special case when they're in the gas phase.
This was my impression too
the explanations after 3:30 and 6:00 seem to contradict each other. Is the sky coloring the result of scattered light or non scattered light that reach us?
Blue light gets scattered away from the direction of the Sun, and can reach us from any direction after being scattered many times. This is why the sky looks blue in all directions. At sunrise and sunset the sky itself is still blue. What you see as spectacular sunrises/sets is the light that is NOT scattered, but instead reflected off clouds and dust. On a very clear day sunrises and sets are in fact very bland an boring. When the Sun is low in the sky, its light passes through more atmosphere, and even more scattering can occur. Thus, the Sun itself will appear to have lost the blue colours, and appear orange or red.
In other words, if no light arrived to your eyes from an area of the sky which is not right next to the sun, it would appear black. The light that does arrive from the sky far from the Sun has gotten there by scattering. Blue light scatters more, which is why you see mostly blue light from those directions. At sunrise/sunset you are looking in the direction of the Sun (obviously). Thus you are not seeing all the light that is scattered, you see what is left, the light that did not scatter.
@@michaeldamolsen wonderful explanation!
It is said, to see something, it's size must be greater than wavelength of light. Why is it so?
Does this mean that cameras also have trouble seeing violet?
Early digital cameras DID have trouble with monochromatic violet. Example, violet plants appeared blue. For unknown reasons, it's rarely mentioned that the red cones in our eyes also have some sensitivity to wavelengths of around 380 nanometers (violet). So monochromatic violet light actually stimulates both blue AND red cones, otherwise we could never see monochromatic violet as a different color. In some early digital cameras, the red sensors had zero sensitivity to violet and could not faithfully reproduce that color. Anything violet would appear blue in the picture.
@@davethedaemon9024 What? So... if I understand this right, because of how our eyes work we _do_ see violet as purple? That is so weird. I was like, why is this guy calling violet purple when there's no red in it.
But then purple still isn't a colour that exists in the world and no matter if we see violet or red and blue, we see a purple colour that exists only in our brains. Not that that's not weird XD
It still annoys me that he says the sky _is_ blue. Next thing you know he tells us that because we're so low on the surface of this planet that the planet _is_ flat. Maybe to a photon coming towards it it physically is, but I'm pretty sure that relativity doesn't make a curved surface physically flat to massive objects on the surface, just as scattering doesn't alter the physical properties of the sky to make it blue.
Một mái ấm thật hạnh phúc Chúc thầy ngày càng thành công Luôn theo dõi và ủng hộ thầy lộc ❤❤❤️
Physics is Everything
No it isn't because there's nothing in physics that can convey what our experience of blue is to someone who's never seen blue before. You can say it's 500 nm light but they still won't know
Given that a lot of ancient literature refers to "wine dark seas" could it be that 2000 years ago humans had a violet detecting cone that we have since lost?
No… it is likely just the way they interpreted the dark color of the ocean
There was a hypothesis that the water commonly used to water down wine in those days might be alkaline due to limestone content, it might change the hue of the wine towards the blueish. However, it is more widely believed that it is simply a poetic expression, perhaps referring more to the darkness rather than the hue. While trying to find references on this, I came across a delightful New York Times article from 1983 of the title "Homer's Sea: Dark Wine?" you should find it easily by searching for that :-)
Also noticed that (according to the graph in the video) the Sun's output in violet is significantly less than its output in blue -- if we were on a planet orbiting in the habitable zone of a class B star, the sky might indeed have a shade of violet in it (although the lesser but still significant scattering of green light would keep the color from being totally in the short wavelength range, as it does on Earth).
The amount of violet light is just slightly(5-10%) lower than the amount of blue light
No stars can be violet this happens because the peak is in ultraviolet/violet, but a large about of the other colors is emited making the star look whitish-blue
@@HugoFilho. A very hot star wouldn't appear violet (unless viewed through a really weird atmosphere), but the sky could appear violet from scattering the light of a very hot star.
Why does some people call something that is clearly brown, for red?