Astronomy Question:

Clouds are formed as part of the water cycle. Effectively, warm air rises. Indeed, water vapor rises, as it is lighter than air.

However, as it rises through the sky, higher and higher up, the air is colder.

This causes the water vapor to condense and it turns to liquid droplets. This is what causes a cloud to form and condense.

When the density is high enough, the water escapes from the cloud and falls to earth as a cloud.