Clouds appear grey because they are thick and contain a large number of water droplets or ice crystals (called hydrometeors). When the concentration and size of these particles increase, less sunlight can penetrate through the cloud, leading to multiple scattering and absorption of light inside the cloud. As a result, less light reaches the underside of the cloud, making it look darker or grey from the ground. In contrast, clouds with smaller droplets that allow more sunlight to pass and scatter diffusely appear bright white. This effect is especially noticeable in rain clouds that are dense and heavy with moisture, causing the classic grey appearance before rain falls.
Explanation in detail
- Clouds are made of water droplets or ice crystals that scatter sunlight in all directions.
- Small droplets and fewer particles scatter light diffusely, making clouds look white.
- As clouds grow thicker and denser, they block more sunlight from passing through, causing the bottom parts to receive less light and appear grey.
- Larger droplets in rain clouds absorb more light and scatter less, enhancing the grey or dark appearance.
- The grey color is therefore a result of the cloud's thickness, particle concentration, and the scattering and absorption of sunlight inside the cloud.
This phenomenon explains why clouds can vary in color from bright white to dark grey depending on their composition and thickness.
