THINGS AROUND US
3. COLOR OF CLOUDS
A single and distinct luminous body causes stronger relief in the objects than a diffused light; as may be seen by comparing one side of a landscape illuminated by the sun, and one overshadowed by clouds, and illuminated only by the diffused light of the atmosphere.
— Leonardo da Vinci
What is a cloud?
Technically a cloud is an material made up of two or more substance consisting of fine solid, liquid and gaseous particles (mainly liquid droplets, frozen crystals of water in case of earth) which are suspended in the atmosphere of a planet.On Earth, clouds are formed as a result of saturation of the air when it is cooled to its dew point, or when it gains sufficient moisture (usually in the form of water vapor) from an adjacent source to raise the dew point to the ambient temperature. Dew point is the point at which air must be cooled to become saturated with the water vapor. On earth clouds start forming from 2 km from the ground level.
Cloud literally means "mass of stone" because of its appearance before rain. There are different type of clouds based on their height, pattern and composition.
what is color?
Color is a characteristic of visual perception described by various categories like red, yellow,green etc. Simply is the ability of human to identify a spectrum of electromagnetic wave when it is reflected or refracted. The rainbow is the best example of the spectrum of electromagnetic waves that human can see.
https://phys.org/news/2015-08-resplendent-inflexibility-rainbow.html
Why do clouds have color?
Mostly clouds are white, gray, black, orange, red, yellow etc. Some colors shows up only during evening, some in morning, some in certain climatic condition, some during noon etc. So it can be seen that the color of clouds change with the position of sun.
The light of the Sun is composed of all the colors of the rainbow. But as it makes its way through the atmosphere it scatters in all directions off air molecules and very tiny dust particles (much smaller than a micron, which is 1/250,000 of an inch). This is called Rayleigh scattering.Blue light scatters the most of all colors, about five times more than red light. Thus when you look at the sky during the day in any direction, blue dominates, which is why the sky is blue. If you look at the sky from the surface of the Moon (you may have seen pictures), the sky is not blue—it’s black, like our sky at night. Why? Because the Moon has no atmosphere.
In simple words, The water drops in clouds are much larger than the tiny particles that make
our sky blue, and when light scatters off these much larger particles, all the colors in it scatter
equally. This causes the light to stay white. But if a cloud is very thick with moisture, or if it is in the shadow of another cloud, then not much light will get through, and the cloud will turn dark.
So from this we can see that the size of the particles in the cloud, the position of the clouds and composition of clouds are responsible for the color of the clouds.
Different color of clouds
Photo by J Jude Felix and J John Paul
True color of clouds
Due to larger size of the cloud particles the light are not scattered much so, the cloud looks white. Thick and heavy moist clouds before rain the clouds look dark (i.e. grey and black).During sunrise and sunset, the Sun is very low in the sky and so light has to travel through more of the atmosphere. As a result more of the blue light is scattered and deflected away allowing more red and yellow light to reach the Earth thus the cloud looks red, yellow or orange in color.
In reality clouds are actually colorless, because water and ice are colorless. But there is a catch. The water droplets can absorb and reflect light. This is why they appear white when light is reflected from them. They can also take on a darker gray color when the cloud absorb light or blocks the light to reach one’s eye.
