The sky is blue, Sun is yellow, but the clouds are white! The Sun emits all of the colors in the visible spectrum. When you combine all of those colors, you get white. The Sun is emitting white light, and clouds contain tiny round water droplets. When that white sunlight passes through those tiny droplets, they are scattered in all directions. That’s why clouds are white.
The light from the Sun, which we all know is white, is a mixture of rainbow colors. We see different colors from that braid being split by reflecting part of that light absorption or some of that light or refraction, splitting apart of that weave.
Why clouds are white?
Inside a cloud, there are millions of tiny water droplets, and these act like refraction prisms. They split the light apart into all of the colors of the rainbow. Water droplets are doing the same thing, and they’re sending these different colors into one another, creating a mixture effectively. What happens is that light gets blended back together like mixing colors of paint until you get white.
Clouds are not consistent but do not have the same density. They’re not located at the same height, and above all, they do not have the same color. Why is it that some clouds seem to be darker than others? Two main factors play a significant role in this phenomenon: sunlight and cloud density.
Now besides all the differences of the clouds, they do have one thing in common. They all block sunlight, and sunlight travels through space in different wavelengths. Some of which is reflected into space. Once they hit the Earth’s atmosphere, some others are scattered. Once they entered the atmosphere, many wavelengths eventually make it to the Earth’s surface.
Clouds consist of particles. The diameter is larger than the wavelength of a visible spectrum reflecting in scattering light equally, making them wide. Water vapor floats into the air accumulating masses which are called clouds. Some of them are denser than others because they contain more water. Visible light finds it challenging to pass through those clouds. It means that reflectivity is greater than invisibility. We may see them darker as a result because we are standing beneath them. But if you are on a plane traveling over those clouds, they will appear white.
As a result of the reflective ability, those clouds do not accumulate water vapors forever. They do have a threshold, and once this threshold is breached, water precipitates. That is why we have associated our clouds with rain. Water does not always form clouds, depending on their density and atmospheric pressure. They can create a haze sheet in the troposphere, which is the lower part of the atmosphere.
High levels of humidity are required for this phenomenon. Fog, smoke, and clouds are all formed from water droplets wandering around the atmosphere due to different atmospheric conditions. They all reflect the light of the visible spectrum equally and depending on their density. They sometimes appear white the sometimes darker in various shades of gray. The color is dependent on their opacity.
Why are clouds grey and darker before the rain?
Clouds are formed when air and water vapors near the ground warm up and rise. As it’s getting higher, the water vapors condense, and the droplets join together to form clouds. The more condensation there is, the more droplets there are. When light from the Sun passes through these significant accumulations of water vapors, the droplets scatter the light in all directions.
The droplets are tiny and spread out enough to scatter the entire spectrum of light, which means that they will appear white. The more water droplets gather, and the clouds grow larger. Less light can penetrate through the cloud. What we see from the ground seems grey because less light is being scattered to our eyes as the water droplets within the cloud get larger. This effect is enhanced, which is why clouds appear much darker just before it rains.
Read More: Is The Sky Blue?
Met Office, ed., “Difference Between Mist and Fog.”
World Meteorological Organization, ed., “Nimbostratus, International Cloud Atlas.”
Clouds Online. “Cloud Atlas.”
Koermer, Jim. “Plymouth State Meteorology Program Cloud Boutique.” Plymouth State University.
American Meteorological Society. “Glossary of Meteorology.”
Hatheway, Becca. “Cloud Types.” Windows to the Universe, US National Earth Science Teachers Association (NESTA).