Basic purpose of this lecture is to present on Cloud Formation. Masses of small water droplets or tiny ice crystals that float in the air. Three main types are cirrus, cumulus, and stratus. Other clouds are a mixture of these three main types. Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere.