The formation of clouds has always fascinated man. You must be curious to know how the clouds are formed and the various types of clouds. We know that the water of the rivers, ponds, lakes and seas is converted into vapour by the heat of the sun and this vapour mixes with the air. Hot air, mixed with water vapour, being lighter, begins to rise up in the sky. When the air mixed with water vapour accumulates at one place, it gives the appearance of smoke, which we call cloud. Although there are ten different types of clouds, they can actually be divided into four major types. These categories have been created on the basis of the different shape, size and colour of clouds. 1. Cirrus clouds: Cirrus clouds are formed at great heights. They are white in colour and look like birds’ feathers. Their height ranges from 8,000 to 11,000 metres. They are made up of small ice particles. 2. Stratus clouds: Stratus clouds are formed at a height of about 2,438 metres. They look like a smooth even sheet. They predict bad weather and often cause drizzle. 3. Cumulus clouds: Cumulus clouds are formed at a height of 1,219 to 1,524 metres. They are dome-shaped at the top and flat at the bottom. They are layered in appearance and look like white mountains in the sky. 4. Nimbostratus clouds: Nimbostratus clouds are formed at the low heights. They are deep brown or black in colour. These are the clouds, which cause rain. And how do the clouds create rain? If the air below the clouds carrying condensed water vapour is cool, the size of the water droplets present in the clouds keeps increasing till they attain an optimum size, and when that happens they fall down on the Earth in the form of rain. Similarly, if the air below these clouds is not cold, the water droplets present in the clouds will be reconverted into vapour. If this happens then the clouds will float away without raining.