Clouds are masses that can be seen from droplets of water or frozen crystals suspended in the atmosphere above the surface of the earth or the surface of other planets. Clouds are also visible masses that are attracted by gravity, like the mass of matter in space called interstellar clouds and nebulae. 
Clouds are studied in the science of cloud or cloud physics, a branch of meteorology. On Earth the substance is usually the precipitation of water vapor. With the help of air hygroscopic particles such as dust and salt from the ocean, small water droplets form at low altitudes and ice crystals at high altitudes when air is cooled to saturation by convective local or larger raised non-convective scales. On some issues, high clouds may be partially composed of super-cold water droplets. Droplets and crystals are usually about 0.01 mm (0.00039 in) in diameter.
Most commonly from day-to-day solar heating from the air at the surface level, the frontal lift that forces the warmer air masses to rise further upward and lift the air orographic over the mountain. As the air rises, it expands so that the pressure decreases. This process releases energy that causes cold air. When surrounded by billions of other droplets or crystals they become visible as clouds. In the absence of a condensation core, the air becomes saturated and cloud formation is inhibited. in solid clouds showing high reflections (70% to 95%) across the clouds seen in various wavelengths, making it appear white, above.
Dewdrops (water droplets) tend to efficiently diffuse light, so the intensity of solar radiation decreases with the depth of the direction to the gas, then the gray or even dark colors sometimes appear at the bottom of the cloud. Thin clouds may appear to have acquired colors from their surroundings or backgrounds and clouds illuminated by non-white light, such as at sunrise or sunset, may appear colored accordingly. Clouds appear darker near-infrared because water absorbs solar radiation at wavengths.