Why is the Sky Blue in the Daytime?

As sunlight passes through the atmosphere, its light becomes scattered by air molecules. Light with shorter wavelengths such as blue is dispersed more widely than other colors such as red.

Rayleigh Scattering causes this effect and gives the sky its signature blue hue, particularly nearer the horizon.

The Sun

Light travels through Earth’s atmosphere before reaching its surface and is scattered as it travels. Different wavelengths are scattered differently, and because blue light has shorter wavelengths than other colors it tends to spread more widely during daytime – hence why the sky often appears blue during this period.

Violet light has longer wavelengths than blue light, preventing it from scattering as readily. If violet light were to spread evenly around, however, daytime skies would appear as pure violet hues; but as human eyes are more sensitive to blue than violet wavelengths and more of Earth’s atmospheric sunlight contains bluer wavelengths than violet ones, the sky remains bluer.

At sunset and sunrise, the sky turns red due to Tyndall scattering – an effect caused by larger particles than those affected by Rayleigh scattering; more importantly, Tyndall scattering is most prominent at higher altitudes with greater particle accumulation in the atmosphere. As a result, blue and green wavelengths become dispersed more evenly, leaving red wavelengths dominant from Earth’s perspective.

But even at lower altitudes, Rayleigh scattering remains the key factor in determining the sky’s color. When the sun is low on the horizon, most of its blue light has already been dispersed by air molecules; leaving only orange, yellow and red wavelengths of sunlight reaching your eyes; this phenomenon accounts for why sunsets appear reddish-pink.

Science can explain how an astronaut in space can see the moon clearly despite its blue tint, although its true hue is white. Because the Sun and Earth’s atmosphere cast strong blue lights onto its surface, we perceive it as blue – and similarly for distant stars illuminated by Sunlight.

The Atmosphere

As the Sun passes through Earth’s atmosphere, its light is broken down into different hues by Rayleigh scattering. As sunlight travels through, molecules in the air scatter shorter blue wavelengths more efficiently than longer red ones; as a result, most of what reaches your eyes is blue light.

Without an atmosphere, Earth would appear completely black; similarly, as there is no atmosphere surrounding the Moon it remains entirely dark during both daytime and nighttime hours.

Sky appears blue because our atmosphere contains gas molecules. White light from the Sun passes through this layer and hits these gas molecules, where it gets refracted in all directions; shorter wavelengths like blue and violet light get refracted most intensely, giving rise to scattered lighting that your eyes perceive as blue hue.

The atmosphere consists of several distinct layers with their own temperatures, pressures and phenomena. The troposphere lies close to Earth’s surface and is where most weather occurs; above it lies the stratosphere with its protective ozone layer and jet aircraft flight paths.

At higher elevations in the atmosphere, fewer molecules scatter light; this allows only short wavelengths of sunlight through. Therefore, skies at these heights tend to appear dark blue or bluish-violet.

As the Sun rises and sets each day, its path passes through most of the troposphere resulting in its light being filtered by various layers into blue when approaching the horizon and red again when disappearing below it.

The thermosphere’s upper edge – often associated with outer space – extends 550 to 1,000 kilometers (341 to 621 miles). Unfortunately, not much is known about this layer but solar radiation heats it and contains some of the largest particles found within our atmosphere.

Clouds

The sky’s beautiful hue results from its abundance of air molecules. When sunlight passes through its atmosphere, these air molecules scatter it, altering both its direction and intensity. Light with shorter wavelengths like blue is scattered more than red light due to the presence of shorter molecules; as a result, blue lights dominate during daytime hours in the sky.

Rayleigh scattering was named for Lord Rayleigh who first observed it in 1870’s. He discovered that intensity of scattering depends on fourth power of wavelength with blue light being more scattered than other colors.

Since our eyes are particularly sensitive to blue hues, this could explain why the sky appears so blue. If the Earth were completely transparent and its atmosphere completely transparent it would probably appear white or grey instead of being colored blue by human perception.

At sunset and sunrise, the cause for its vibrant orange/red hue lies deeper within. As the Sun moves lower on the horizon at these times, more of its light must travel through more atmosphere – this causes more blue and violet light to be scattered out of our line of vision, thus allowing longer wavelengths like red to reach our eyes more readily – giving rise to its characteristic hue at these times.

Water droplets within clouds reflect and scatter light, contributing to the blue hue of the sky at dusk and dawn and creating vibrant sunset clouds. We refer to these phenomena as sunset clouds.

The thin atmosphere of the Moon does not feature its familiar blue hue; instead it displays an earth-tone hue due to dust particles in its stratosphere that reflect and scatter sunlight, especially near volcanic eruptions when large amounts of material are lifted into space and dispersed through solar winds.

The blue hue of Earth’s atmosphere is due to water vapor and other gases larger than visible wavelengths in its atmosphere, such as carbon monoxide. These particles scatter and absorb blue sunlight from the Sun while leaving only reddish light for us to perceive; hence why Moon appearance changes from night to day as it moves across sky.

The Rainbow

When the sun is out, our eyes naturally perceive a blue sky due to their construction. Light rays from the sun travel all the way down into our atmosphere where air molecules scatter them; blue wavelengths tend to be scattered more readily than red ones due to how sensitive our vision is for colors other than blue and violet hues. As a result, when exposed to direct sunlight we perceive it as blue because our retinal receptors are more responsive than red and green hues.

Rainwater droplets act like miniature prisms when sunlight passes through them and bends and separates into all the colors of a rainbow, due to having differing densities depending on size and shape of water droplets; violet wavelength has the shortest bend radius while red has longest.

Water droplets reflect back at us at various angles, creating the arc that gives a rainbow its signature look – red is closest to you while blue stretches out to meet the horizon. Since sunrise and sunset bring different angles of sunlight through Earth’s atmosphere into play, this means the rainbow never moves in an exact linear fashion across the sky from one location to the other.

Our eyes have the capacity to detect an array of wavelengths and can distinguish even subtle variations between them – this explains why you can spot someone across a room even with only inches of air between you. However, certain colors are more sensitive than others to our sense of color perception, thus explaining why the sky seems bluer during daylight hours than night.

Eye receptor cells respond more strongly than others to blue and violet wavelengths; as a result, we perceive the sky to be predominantly blue even though there’s plenty of red and orange in it too; other wavelengths tend to be less noticeable, so when clear skies arise it appears bluer than ever.