One of the most common sights in nature are clouds- white and fluffy, gray and overcast, or the brilliant colours they turn into at sunset. In terms of weather they are simply visible masses of tiny water droplets and a whole branch of study called cloud physics is dedicated to understanding this cotton candy-looking phenomenon.
But, what are clouds made of?
When the sun shines over rivers, lakes and oceans of the world it heats up the surface of the water. The water turns into gaseous water vapour on being heated and begins to rise into the air. As it goes higher, the water vapour begins to cool down and turns back into water droplets. The temperature at which water condenses is called the dew point. The dew point is not a constant because it depends on the amount of water present in the air.
These water droplets in clouds are so tiny that they hang suspended high up in the earth’s atmosphere. Over a period of time condensed water vapour accumulates to form clouds. The water droplets higher up in the cloud are colder than the droplets below to the extent that some parts of a cloud can even contain small bits of ice. After a while the cloud becomes heavy with water droplets and gravity brings the water droplets back down as rain. So now you know how clouds are formed.
But why do clouds appear white?
Clouds appear white because they allow light to pass through it. Since sunlight is white, the water droplets simply act like a canvas upon which the sun throws its rays. When trillions of water droplets get together in one cloud, they allow less and less light to pass through it thus giving it a dark gray hue. This is also how we know that it is about to rain.
Water vapour is the same ingredient in the atmosphere that is responsible for making rainbows. Can you say why clouds are white and not rainbow coloured?
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