Why are clouds white?

We all have spent time trying to find faces and create shapes in the fluffy, white clouds that float in our skies.

Clouds are those gaseous bodies that we see in our sky, often a deciding factor of the weather. 
 
In meteorology, a cloud is an aerosol consisting of a visible mass of minute liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space.

We can breakdown down this definition to understand them more thoroughly.

Aerosols can be defined as a suspension of fine solid particles or liquid droplets in air or another gas. Clouds contain a visible mass.

This mass can vary and can be in multiple forms such as rain, snow, etc.

Water or various other chemicals may compose the droplets and crystals. 
 
Clouds are very significant in moderating and changing the temperatures of a particular region. Droplets of water or ice particles suspended in clouds, as well as bits of dust and other particles floating in the air, called aerosols, reflect and absorb light and heat coming into and leaving our planet.
 
One common question that many people have is why are clouds white? 

Clouds are white because the light from the Sun is white.

As this light passes through clouds, it ends up interacting with the water droplets inside.

These are much bigger than the atmospheric particles that exist in the sky. 
 
When this sunlight reaches an atmospheric particle present in the sky, blue light is scattered away more strongly than any other color.

This gives the sky the color blue. 

This same phenomenon occurs in clouds with a variation. In clouds, sunlight is scattered by much larger water droplets.

These end up scattering all the colors present in the spectrum equally.

This sunlight continues to remain white and so making the clouds appear white against the background of the blue sky.
 
Sunlight or 'visible light' can be thought of as a wave and a part of the electromagnetic spectrum.

We can witness the full spectrum when it is split up and spread out as a rainbow.

This spectrum is also shared with other types of waves.

For example; short x-rays and gamma rays to long radio waves.
 
Each visible color has a different wavelength.

Blue light has the shortest wavelength at 400 nanometres and red light the longest at 700 nanometres.

Smaller particles can scatter the shorter wavelengths more effectively and easily.

Especially those that are invisible to our eyes in the atmosphere, making the sky blue.
 
Bigger particles like water droplets within a cloud scatter all wavelengths with roughly the same effectiveness.

If we consider that there are millions of water droplets in a cloud, the scattered light interacts and combines to generate a white color.
 
Cloud bases are often grey as a result of the same scattering that makes them white.

When light is scattered in a cloud, it is usually sent back upwards.

The other possibility is that the light scattered is sent out to the sides of the cloud, making the tops and sides of the cloud whiter than the base which receives less light.
This occurrence is more prominent in the clouds that bring rain because in this situation the cloud droplets are bigger.

This leads to them scattering more light.

Furthermore, this means that even less light from the Sun reaches the bottom of the cloud, giving rain clouds their intimidating appearance.
 
This is because the tops of clouds have a constant source of white light, they are always white.

While traveling on an airplane, when one looks out of the window and observes that they are above the clouds, one will notice that the tops of all the clouds will be a brilliant white.
 
At sunrise or sunset, clouds can take on a red or orange color.

This happens because at this time the Sun is very low in the sky and so light has to travel through more of the atmosphere.

This causes a larger scattering of the blue light. This deflects away allowing more red and yellow light to reach the Earth.