Kathy Brown, age 13, of Peoria, I11., for her question:

WHERE ARE THE CLOUDS ON A CLEAR DAY?

Clouds are made of misty moisture, just like the foggy stuff that clings to the ground on a misty morning. This cloud material is mini droplets of liquid water, small enough to hang suspended in the air. A slight change in temperature can change this liquid water into water vapor, which is an invisible gas like the other assorted gases of the air.

The change from liquid water to gaseous water is governed by strict weather regulations. It so happens that the air can contain so much water vapor  and no more. And the amount depends upon its temperature. When the air chills, some of its gaseous vapor becomes misty droplets of cloudy moisture. For example, warm moist air rises and chills, forming clouds aloft.

In warm, sunny weather the thirsty air evaporates cloud moisture   which    becomes invisible vapor and disappears. The same thing occurs when the warm sun burns off the morning mist.