### Why the colour of sky is blue?

As we know that there are different colours in the world like blue, white, red, yellow and so on but when we see at the sky, a question comes to our mind that why the colour of the sky is blue instead of white, red, yellow or any other colour. It is a complicated concept and before understanding this concept, we have to understand some other things.

## Sunlight

Sunlight is the major casue of the blue color of the sky. We see that the colour of sunlight is yellow but it is not the actual colour of sunlight. The actual colour of sunlight is white and white light is a combination of seven colours. The seven colours of white light are given below;

 Sr. Number Color Name 1 Violet 2 Blue 3 Indigo 4 Green 5 Yellow 6 Orange 7 Red

## Wavelengths of different colours of light

The wavelengths of these seven colours of light are also different from each other. The wavelength of violet colour is 380-450 nanometers. The wavelength of blue colour is 450-485 nanometers. The wavelength of indigo colour is 485-500 nanometers. The wavelength of green colour is 500-565 nanometers. The wavelength of yellow colour is 565-590 nanometers. The wavelength of orange colour is 590-625 nanometers. The wavelength of red colour is from 625-740 nanometers.

 No. Color Wavelength 1 Violet 625-740 nm 2 Blue 625-740 nm 3 Indigo 625-740 nm 4 Green 625-740 nm 5 Yellow 625-740 nm 6 Orange 625-740 nm 7 Red 625-740 nm

Related post: Why Is Milk White?

## Scattering phenomenon

The scattering of the sunlight is becoming the main cause behind the blue color of the sky. According to the Rayleigh scattering formula, the light which has smaller wavelength scatters more and the light which has larger wavelength scatters less. In the above seven colours of sunlight, the violet colour scatters more. After that, the blue colour scatters and so on.

# The visible wavelength of the light

The portion of the electromagnetic spectrum that is visible to a human eye is known as the visible spectrum. The electromagnetic radiation in this range of the wavelengths is known as the visible light. A human eye can see only that light whose range is in between 400-740 nanometers.

# Why the colour of the sky is blue?

When the sunlight which is a combination of seven colours (Violet, blue, indigo, green, yellow, orange and red) enters into the atmosphere of our earth, it is scattered by the gasses and other particles that are present in the atmosphere of the earth. According to the scattering phenomenon, the violet light scatters more but the scattering wavelength of this light is less than 400 nanometers which is invisible for a human eye. After that blue light scatters and the wavelength of blue light is from 450-485 nanometers and this wavelength of the light is easily visible for a human eye. After that other colours of light are scattered. Due to the scattering dominance of the blue light over the other colours of light, the colour of the sky seems blue to us.

## Why the colour of the sun is yellow?

As we have discussed earlier that actual colour of the sun is white instead of yellow. According to the scattering phenomenon, violet, blue, indigo and green colours of light have smaller wavelengths, therefore, these colours of light are easily scattered. On the other hand, other colours of light like yellow, orange and red are not easily scattered. That’s why the colour of the sun is yellow.

# Is the sky blue because of the ocean?

Most of the people think that the blue colour of the sky is due to the blue colour of the ocean. It is totally a misconception because the blue colour of the sky is due to the scattering of the sunlight. Now, another question comes to our mind that why the colour of the ocean is blue? NOAA (National Oceanic Atmospheric Administration) has provided the answer to this question. According to NOAA, the water can easily absorb the shorter and longer wavelengths of light. Therefore, when sunlight hits the ocean, it absorbs its longer wavelengths like red, yellow, green and orange along with its shorter wavelength like violet. Therefore, there remains only a blue wavelength of light. This blue wavelength of the light is reflected by the ocean that gives blue colour to the ocean.

# Why is the Mars sky red?

The Viking Mars Landers has sent some photos of Mars sky. It is clearly seen in these pictures that the colour of Mars sky is red instead of blue. According to scientists, the red colour of the Mars sky is due to the dust storms which occur from time to time on Mars. These dust storms throw iron-rich dust particles into the atmosphere of Mars. These iron-rich dust particles are the main cause of the red colour of Mars sky. The scientists have also predicted that the colour of the Mars sky also changes with the changes in the weather conditions. If there are no storms for lots of time, the colour of the sky will be blue.

# Why are clouds white?

As we know that there are some particles of water in the atmosphere of earth. These particles of water are bigger than other particles of the atmosphere. When the white light of the sun strikes with these water particles, these water particles scatter all the wavelengths of light in equal amount. This combination of all the wavelengths of light provides white colour to the clouds.

# Why are rain clouds dark?

It is a fact that most of the clouds are white but the rain clouds are darker shade of grey. The water on our earth changes into water vapours due to warmer earth and these water vapours are less in weight and they rise up. When these water vapours enter into the higher atmosphere of earth, they have to come across with cooler air. The cooler air condenses these water vapours. As a result, they form clouds. No doubt, these water droplets reflect all the colours of sunlight and these are white in colour but when lots of water droplets are gathered, they become thicker and denser. The upper side of these thicker and denser clouds reflects all the colours of light and they don’t allow the light to penetrate through. That’s why the lower side of the rain clouds has a darker shade of grey.
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