What causes the patches of light and dark in the night sky on a full coverage cloudy night sky?

The patches of light and dark in a fully covered cloudy night sky are primarily caused by variations in cloud thickness and density. Thicker clouds may block more starlight, creating darker areas, while thinner or more transparent spots allow some light to pass through, resulting in lighter patches. Additionally, the presence of the moon or artificial lights can enhance these effects, casting illumination that interacts with the clouds. Lastly, atmospheric conditions can also play a role, affecting how light is scattered and absorbed.