Carol Jannotta, age 11, of Arlington Heights, I11., for her question:

WHERE DOES DEW COME FROM?

Often you'll find dew covering all of the objects that are outdoors over night. Dew forms when moist air is cooled by direct contact with cold objects in the open. The process is called condensation.

Such things as blades of grass, leaves and sometimes the family auto receive heat from the sun during the day by direct radiation. These objects lose the heat at night, also through radiation. Since radiation is more effective on clear nights, objects in the open cool down faster when the sky is clear than when it is cloudy. As the objects cool, the air next to them cools too. when this air reaches the dew point, it can no longer hold all the moisture present. It deposits this excess moisture as dew.

When the temperature falls below the freezing point, frost forms instead of dew.