Why is the sky blue (and the sun yellow)?

Summary

This script delves into the fascinating science behind the colors we see in the sky. It explains why the sky appears blue due to the scattering of blue light by atmospheric molecules, which are more effective at scattering shorter wavelengths. The script also addresses why the sun looks yellow and sunsets red, illustrating how sunlight's colors change as it passes through the atmosphere. An experiment with a flashlight and milk in water visually demonstrates these concepts. The explanation extends to why clouds appear white, as larger water droplets scatter all colors equally. This educational narrative provides a clear understanding of light scattering and its impact on the colors we perceive in the sky.

Takeaways

• 🌏 The sky appears blue because atmospheric molecules scatter blue light more than other colors due to its shorter wavelength.
• ☀️ The sun appears yellow to us because the blue light is scattered away by the atmosphere, leaving the longer wavelengths like green, yellow, and red.
• 🌅 During sunrise and sunset, sunlight passes through a greater thickness of the atmosphere, which scatters shorter wavelengths like blue and green, leaving the longer red and orange wavelengths to dominate.
• 🌈 White light is composed of seven colors (VIBGYOR), each with different wavelengths, with violet having the shortest and red the longest.
• 🔬 The scattering of light by atmospheric particles is more pronounced for shorter wavelengths like blue, which is why we see the sky as blue.
• 🚫 The sun does not produce much violet light, and our eyes are less sensitive to it, so we don't perceive violet in the scattered light.
• 💧 Clouds appear white because they are made up of water droplets larger than the wavelength of light, which scatter all colors equally, resulting in white light.
• 🧪 An experiment with a flashlight, water, and milk can demonstrate how particles in a liquid scatter light, with milk particles mimicking the scattering effect of the atmosphere.
• 🌌 Without an atmosphere, the sky would appear dark except for the white sun, as there would be no scattering of light in other directions.
• 📉 As sunlight passes through more of the atmosphere (as during sunrise/sunset), shorter wavelengths are scattered away, leaving the longer, less scattered wavelengths like red and orange.
• 🌉 The beauty of sunrise and sunset is partly due to the direct visibility of the sun without the intense scattering of light that makes it uncomfortable to look at during the day.

Q & A

Why does the sky appear blue to us?

The sky appears blue because the molecules in our atmosphere, such as nitrogen and oxygen, scatter blue light more than red light due to its shorter wavelength.

Why does the sun, which is actually white, often look yellow to us?

The sun appears yellow to us because when sunlight passes through the atmosphere, the shorter wavelength blue light is scattered more than the longer wavelength yellow light, leaving a yellowish hue.

What causes the red color during sunrises and sunsets?

During sunrise and sunset, sunlight passes through a longer path in the atmosphere, scattering away shorter wavelengths like blue and green, leaving the longer wavelengths of orange and red to dominate.

Why do we not see violet in the sky, despite it having an even shorter wavelength than blue?

We don't see violet in the sky because the sun doesn't produce much violet light, and our eyes are less sensitive to violet, resulting in indigo and blue wavelengths being more visible.

What is the scattering of light and how does it relate to the color we see?

Scattering of light occurs when light hits a tiny particle and reflects in all directions. The color we see is the same as the color of the light that is scattered by the particle.

How does the white light from the sun get separated into different colors?

White light from the sun is made up of seven colors (VIBGYOR). The different colors are perceived due to the varying wavelengths of light, with violet having the shortest and red the longest.

Why do clouds appear white instead of blue, even though they scatter light?

Clouds appear white because they are made up of water droplets larger than the wavelength of light, which scatter all colors equally, resulting in the appearance of white light.

How does the size of atmospheric particles affect the scattering of light?

Particles smaller than the wavelength of light scatter shorter wavelengths more than longer ones. However, particles larger than the wavelength scatter all colors equally.

What would the sky look like without an atmosphere?

Without an atmosphere, the sky would appear dark everywhere except for the direction of the sun, which would appear white, as there would be no scattering of light.

Can we recreate the effect of atmospheric scattering with a simple experiment?

Yes, the effect can be demonstrated using a flashlight, a tank of water, and some milk. The milk particles represent atmospheric particles, scattering blue light and making the water appear blue.

Why does the light appear dull during sunrise and sunset, compared to midday?

During sunrise and sunset, sunlight travels through a greater portion of the atmosphere, scattering more light away from the observer, resulting in a dimmer appearance.

Outlines

00:00

🌌 The Science of the Blue Sky and Sunlight Colors

This paragraph delves into the optical phenomena that give the sky its blue hue and the sun its yellow appearance. It explains how the molecules in Earth's atmosphere, such as nitrogen and oxygen, scatter shorter wavelengths of light (blue) more than the longer ones (red). The concept of light scattering by particles is introduced, along with the idea that different wavelengths of light correspond to different colors. The explanation extends to why violet light, despite having an even shorter wavelength than blue, is not scattered as prominently due to the sun's light composition and human eye sensitivity. The paragraph also uses an experiment with a flashlight, water, and milk to visually demonstrate how an 'atmosphere' scatters light, leading to the perception of a blue sky and a yellow sun.

05:02

🌅 Explaining the Yellow Sun, Red Sunsets, and White Clouds

The second paragraph continues the discussion on light scattering, focusing on why the sun appears yellow and sunsets/red sunrises take on a reddish hue. It describes how the sun's white light, after losing its blue components due to scattering, is left with a combination of green, yellow, orange, and red, which we perceive as yellowish. The paragraph then explains the dramatic color change during sunset and sunrise, which occurs when sunlight passes through a greater depth of the atmosphere, scattering away shorter wavelengths and leaving the longer, redder wavelengths to dominate. This results in the orangeish-red color of sunsets. Additionally, the paragraph addresses why clouds appear white, contrasting them with the smaller atmospheric particles. It clarifies that larger particles, like water droplets in clouds, scatter all colors equally, reflecting white light, which is why clouds, fog, and mist all appear white to us.

Keywords

💡Atmospheric Molecules

Atmospheric molecules refer to the microscopic particles present in Earth's atmosphere, including nitrogen and oxygen. These molecules play a crucial role in the video's theme by participating in the scattering of light, which affects the colors we see in the sky. For instance, the script explains that these molecules scatter blue light more than red, leading to the blue sky we observe.

💡Scattering of Light

Scattering of light is a physical phenomenon where light is dispersed in multiple directions when it interacts with particles. In the context of the video, scattering is key to understanding why the sky appears blue and the sun appears yellow. The script describes how light hitting atmospheric particles scatters shorter wavelengths like blue more than longer ones like red.

💡Wavelength

Wavelength is the distance between two consecutive points in a wave that are in the same phase. The video script uses the concept of wavelength to explain the different colors of light. It states that shorter wavelengths (like violet and blue) are scattered more by the atmosphere, while longer wavelengths (like red and yellow) are scattered less, affecting the colors we perceive.

💡VIBGYOR

VIBGYOR is an acronym representing the seven colors of the rainbow: Violet, Indigo, Blue, Green, Yellow, Orange, and Red. The script introduces VIBGYOR to explain that white light is composed of these seven colors, and how their scattering by the atmosphere contributes to the colors we see in the sky and the sun.

💡Sunrise and Sunset

Sunrise and sunset are the times of day when the sun appears above or below the horizon, respectively. The video script discusses the colors seen during these times, explaining that the longer path sunlight travels through the atmosphere at sunrise and sunset scatters shorter wavelengths, leaving primarily the longer wavelengths like red and orange to create the red sky.

💡Experiment

In the script, an experiment is proposed to demonstrate the scattering of light using a flashlight, water, and milk. This experiment serves to illustrate the concept of light scattering by atmospheric particles, likening milk particles in water to the molecules in Earth's atmosphere that scatter light and create the blue sky.

💡White Light

White light is a term used to describe the composite light that includes all the colors of the visible spectrum. The script mentions that white light is made up of the seven colors of the rainbow (VIBGYOR), and it is the scattering of this white light by atmospheric molecules that results in the blue sky.

💡Indigo

Indigo is a color between blue and violet in the spectrum of visible light. The script explains that although indigo is part of the white light spectrum, it is scattered along with blue light, but we perceive the sky as blue because our eyes are less sensitive to violet light, and the sun doesn't produce much violet light.

💡Clouds

Clouds are collections of tiny water droplets or ice crystals that form in the Earth's atmosphere. The video script addresses why clouds appear white, explaining that because these water droplets are larger than the wavelengths of light, they scatter all colors equally, resulting in the white appearance of clouds.

💡Fog or Mist

Fog and mist are atmospheric conditions where tiny water droplets are suspended in the air, reducing visibility. The script briefly mentions fog and mist in the context of light scattering, stating that like clouds, they scatter all colors of light equally due to the size of the water droplets, thus appearing white.

Highlights

The sky appears blue due to the scattering of blue light by atmospheric molecules more than red.

Sunlight looks yellow because blue light is scattered away, leaving a combination of green, yellow, orange, and red.

Sunrise and sunset appear red due to the scattering of shorter wavelengths, leaving the longer wavelengths of orange and red.

White light is composed of seven colors, 'VIBGYOR', each with different wavelengths.

Light is perceived as a wave, with shorter wavelengths appearing as violet and longer as red.

Atmospheric particles scatter shorter wavelengths more than longer ones due to their size relative to light wavelengths.

Violet light is not seen in the sky because the sun emits less violet and our eyes are less sensitive to it.

Blue light is scattered most by the atmosphere, leading to the perception of the sky as blue.

Without an atmosphere, the sky would appear dark except for the white sun.

An experiment with a flashlight, water, and milk demonstrates how atmospheric particles scatter light.

Clouds appear white because water droplets scatter all colors equally, resulting in white light.

Fog and mist also appear white for the same reason as clouds.

The scattering of light is a complex physical phenomenon involving particle size and light wavelengths.

The experiment shows that as milk particles mimic the atmosphere, the tank glows blue due to scattered light.

During sunset, the light passes through a longer part of the atmosphere, scattering away most colors except red.

The red color of sunset is due to the minimal scattering of longer wavelengths like orange and red.

Transcripts

- Have you ever wondered why the sky is blue?

Why is it that the sun, which is actually

white in color, looks yellow to us?

Why does the sunlight usually look yellow to us?

And why is it that the sunrise

or the sunsets are usually red in color?

Well, the short answer for this

is because the molecules of our atmosphere,

like the nitrogen molecules or the oxygen molecules,

tend to scatter blue light more than red.

So let's explore this in a little bit more detail.

We've talked about scattering of light in previous videos.

Basically, when light hits a tiny particle,

it reflects light in all the direction,

and that's what we call a scattering.

When this scattered light enters our eyes,

we see that particle glowing the

same color that it ends up scattering.

So if it scatters, let's say yellow light,

then the particle will glow yellow to us.

Now, the important thing is that the molecules

of our atmosphere don't scatter

all the colors of light equally.

Now do you understand why that's a little complicated?

Because the physics of scattering

is a little bit complicated.

But in short, what's happening is that

you see, our white light is actually

made up of seven colors: "VIBGYOR,"

the seven colors of the rainbow.

The reason we even see these different colors,

is actually because light is a wave,

or it can be thought of as a wave, like a wave on a string.

And then if you were to look at these waves,

then it turns out that the shorter wavelength then to

hit our eyes, we perceive that as violet.

The longer wavelength then to

hit our eyes, we tend to perceive it as red.

So as the wavelength becomes longer,

the color changes from violet towards the red.

And when we do the physics of scattering,

it turns out that when we're dealing with

particles of the atmosphere which are

much smaller than the wavelength of light,

they always tend to scatter the

shorter wavelength more compared to the longer wavelength.

Okay? We're now going to see why that happens.

As I said, that's a little difficult,

well that's not little, that's actually pretty complicated.

But it turns out that the shorter wavelength,

which we see as violet, so this shorter wavelength,

let's write that down somewhere over here.

So this shorter wavelength scatters the most,

and the longer red wavelength scatters the least.

Therefore, if white light were to come

and hit one of these atmospheric molecules,

then they would tend to scatter blue light

much more than the red light

because blue has a shorter wavelength,

somewhere over here, compared to the red.

Now I'm pretty sure we might be wondering,

"Why blue? Why not the violet itself?"

Because that is an even shorter wavelength, isn't it?

Well, it turns out that the sun doesn't produce

enough of violet in the first place.

So there isn't much violet light

in the incoming sunlight, and therefore

there won't be much violet in the scattered light.

Another reason why we don't see violet

is because our eyes turn out to be

not so sensitive to violet at all.

Combined with these results, we don't tend to see violet,

but we tend to see this indigo blue,

which together we tend to usually call it as blue.

So that's the blue light that

gets scattered the most, and therefore

the atmospheric molecules tend to glow,

they tend to glow blue in color,

when seen from any direction.

Now we are ready to answer all of our questions.

So let's get rid of these pictures.

First, let's look at what we would

have seen if there wasn't an atmosphere.

So let's say it's the daytime,

that means the sun is right above us.

Something like afternoon. Then, the rays of light

would be coming straight down like this.

Now if we were to look in the direction of the sun,

in this direction, then we would see the white sun.

But if we were to look in any other direction,

then there's no light coming towards us

from any of the direction because

all of the light is just falling downwards.

So we would see nothing. Therefore,

all you would be seeing without an atmosphere,

is the white sun and everything else would just look dark.

And you know what? Let's perform an experiment side by side.

All you would need is a flashlight,

a tank of water, and some milk.

When we add milk to this water,

the milk particles are going to

represent our atmosphere.

So if you look at the flashlight directly,

without any milk particles in between,

then all we see is the white light.

And look at the sky, the whole thing has become dark.

Exactly like what we would see

over here without an atmosphere.

But now let's bring in the atmosphere.

When we bring in the atmosphere,

the sunlight strikes all this

atmospheric particles and like we discussed,

they'll end up scattering blue light the most.

They do scatter all the other colors,

but blue light gets scattered the most.

And as a result, almost all these

atmospheric particles will end up glowing blue.

So now, in whichever direction we look,

all we would see is the blue light.

And now in our experiment, if we bring

the tank of water and start adding milk,

the milk particles are going to

mimic our atmosphere. Just like our

atmospheric particles, they are scattering

blue light the most. And as a result

the whole tank is glowing blue.

Because everywhere, the milk particles

are mostly throwing blue light towards us.

Beautiful, isn't it? But did you notice,

as the sky became blue, the sun turned yellow?

Why did it turn yellow?

Well, if you come back over here,

the initial incoming rays are white.

But once it hit the atmospheric particles,

they start scattering blue light.

So from the incoming light, blue got scattered away.

So if you look at the colors that

are remaining now in this incoming light,

violet was never there in the first place, not much,

indigo blue got scattered away,

so now the incoming rays only contain

green, yellow, orange, and red.

Even these are being scattered, but not as much as blue.

So when we combine these colors together,

we get that yellowish glow.

And that's why the sunlight now,

once it has entered the atmosphere,

only retained that yellowish glow.

Because most of the blue has been scattered away.

That's why when we look in the direction of the sun,

the sun starts looking yellow to us.

The same thing is happening in our experiment as well.

All right. Finally, what happens

during the sunset or the sunrise?

Well, the effect or the concept is pretty much the same.

The only difference now is that

the sun is near the horizon.

So let's say the sun is somewhere over here.

Then the rays of sunlight makes its way

through the atmosphere reaching us.

Notice now it's passing through a much longer

part of an atmosphere compared to before.

And so by the time this light reaches our eyes,

not only is the blue light being scattered away,

but pretty much the green and yellow is also gone

because it's hitting so many more atmospheric molecules.

So the only color that survives

are the long wavelengths which get

scattered the least, that is orangeish-red.

Therefore, by the time this light reaches us,

it's going to look pretty much orangeish-red.

We can see the same thing in our experiment as well.

If we look from the top, we can see the light

is passing through the short part

of the tank, only the short part of the atmosphere.

So what we can do, is we can take that tank

and we can turn it so that we make

the light pass through the larger part,

the longer part of the tank.

Now if we see it from the front,

notice the sun turns red, or at least reddish-orange.

Beautiful, isn't it?

Also notice that the light that

is reaching us is pretty dull,

we can hardly see the flashlight now.

That's because most of the light

has been scattered away from us.

That's what makes the sunrise and the sunset so beautiful,

because we can see it directly without hurting our eyes.

To quickly summarize, the reason we see the

blue sky and the red sunset is because when light,

or white light hits these atmospheric particles,

they scatter blue light more

compared to all the other colors.

One last thing I want to talk about before we wind up,

is why are the clouds white in color?

What I mean is that clouds are

made up of tiny drops of water.

So when sunlight hits those drops of water,

shouldn't they also scatter blue light in all the direction?

That means shouldn't the clouds appear blue in color?

Well, it turns out that only those particles

whose size is smaller than the wavelength of light,

only those particles can scatter blue light more

compared to red; or shorter wavelengths

more compared to the longer ones.

They're oxygen, nitrogen molecules.

Now the molecules of the atmosphere

and the milk particles that we find in water,

pretty much fall into that category.

But if the particles become much larger

than the wavelength of light,

in such cases it turns out that

they will scatter all the colors equally.

So drops of water are actually, which are found in clouds,

are much larger than the wavelengths of light.

So when white light falls on them,

they scatter all the colors equally.

As a result they end up scattering just white light.

It is for that reason we will see clouds to be white.

Even fog or mist also fall into that category.

Even they appear pretty white to us.