Carol Anne Seymour, age 13, of Kingston, Ontario, Canada, for her question:

How can the sun's heat reach us through a vacuum?

From lab experiments, we know that sounds cannot pass through a vacuum. From everyday experience, we know that a thin airless space is sealed be¬tween the walls of a vacuum flask    and that it stops heat from passing through. Then we hear that the abundant heat we get from the sun comes to us through 93 million miles of empty airless space. Naturally we wonder how it gets through this enormous vacuum. Actually, it does not travel as heat. The sun's nuclear furnace pours forth a variety of electromagnetic energies, including light and radio. All of these solar radiations travel at the speed of light in longer or shorter wavelengths. When they strike particles of matter, some of the wavelengths are absorbed and changed to heat. This cannot happen in empty space. But when the sun's energy touches the earth, some of its wavelengths are absorbed and this solar radiation becomes heat.