 What color is the sky? I am Yamor, I am Yamor What color is the sky? We don't really spend so much time looking at the sky these days I just take a moment to appreciate this vast, deep blue that is always above us Always there, never ending, in finite But what color is the sky? Your reflex answer is probably blue But it's not It's blue, yeah, during the day Right now, during the sunset it's pink, or red, or orange During the night it's black On a misty morning it's white The color of the sky is very much variable And understanding why the sky is a particular color in a particular situation Was one question that plagued a lot of physicists The one who was able to get the best answer was Lord Riley He named a phenomenon called scattering Scattering is the process where light traveling in one direction is picked up by a molecule and is sent off in another direction I am sitting in a slightly darkened room and I have my phone torch with me If I point this torch at you, then you can see the light from the torch If I point it at my hand, my hand lights up because of the torch But say I pointed at this water You see water is beginning to glow up, but water is transparent You would expect the light from the torch go straight through the water to the other side But if that happens, then you should not be able to see this glow you can see here The reason you are seeing this glow is that some of the light goes through the water And then is reflected in a direction perpendicular to the direction of original travel That happens because of tiny dust particles in the water And because of the molecules of the water itself And this absorption of light by the molecules of the water And their transmission in a different direction to the original direction of travel Is called scattering The same thing happens in the sky Which is why you can see the sky in the first place Even though the angle at which you are looking at the sky Is not the same angle at which the sun is at So what does this have to do with color? You see, color of light originates from this thing called frequency Light is a wave That means it's an up and down motion Of some mathematical quantity we call the electric field And this up and down motion happens a certain number of times per second And that number of times per second is called the frequency of light Now light of different frequencies corresponds to different colors For example, higher frequencies are blue and lower frequencies are red When a material scatters light It doesn't really scatter all the frequencies by the same amount Light scatters different frequencies by different amounts Lord Riley proved that usually the light that is of higher frequency is scattered more As a result, if I have blue light going straight through a medium More of it is reflected to the sides or scattered to the sides And less of it is left traveling straighter through the medium If I have red light traveling through a medium Most of it keeps going straight And very little of it is reflected off to the left and right As light makes its way from the sun to the earth There are two ways it can reach my eyes Way number one is start from the sun Pass through the atmosphere and hit my eye Way number two is through scattering It will not go towards my eye initially It will go towards another part of the atmosphere And that part of the atmosphere absorbs the light And then emits it in the direction of my eyes This second way scattering will occur in different amounts or different frequencies The light you see in the sky is the light from the sun Reflecting in a different direction towards travel Basically the light scattered by the sky from the sun And any material scatters blue light more than red And therefore we can see a blue color sky On the other hand, you can also look at the sky during a sunset When you look at a sunset, you usually don't look at a different part of the sky You look towards the sun Which means the light you are seeing is not the light scattered by some part of the atmosphere The light you are seeing is the light that is not scattered And ends up traveling from the sun directly to your eyes Which color of light is scattered from the atmosphere? Blue So which color remains? Of course it's red So that is why sunsets appear red