R.J. Weir, age 15, of Kingston, Ontario, Canada, for his question:

HOW DOES FROST MAKE PATTERNS ON WINDOWS?

Someone once said that Jack Frost is a pixie artist who specializes in drawing lacy ice crystal masterpieces on windows when the nights are clear and frosty cold. No one has seen the pixie, but the work regularly goes on display and wins raves for its lovely, delicate patterns.

Frost is made when air with moisture in it forms water vapor which is cooled to below freezing temperature. The moisture then condenses and collects on windows and trees.

Frost is usually formed at night and in much the same way as dew. During the day the earth soaks up a lot of heat from the sun. When the sun sets, the earth starts to cool. The surface of the ground cools rapidly, and the moisture which hangs in the air in gas or vapor form begins to condense or change to liquid. If temperatures drop below 32 degrees Fahrenheit, moisture can pass directly from gaseous to solid state and form frost patterns.