Walter Yenser, age 10, of Whitehall, Pa., for his question:

WHY DO FOGS FORM?

Fogs are really very low clouds, usually resting on the ground. A low lying ground fog and a high flying cloud both are made from tiny droplets of water, small enough to float in the air. These misty droplets are made from water vapor, which is mixed with the other invisible gases of the air. When the air becomes chilly, some of this gaseous vapor is changed into misty fog.

During a summer day, the ground warms up 'and sharessome of its warmth with the air above it. At night, the groundcools off  and so does the air. This chilled air must unload some of its vapor. It does this by changing some of its vapor gas into liquid droplets  and a fog is born.

As the morning sun rises higher, the air becomes warmer. The liquid droplets may change back into vapor  and the fog disappears.