Michele Lye, age 10, of Peterborough, Ontario, Canada, for her question:

How does the earth stay warm after the sun sets?

This only happens in summer, when the days are long and the noon sun climbs high in the sky. While the sun shines high, the earth uses some of its radiant energy to warm itself. And it holds onto some of this heat after the sun sets. However, it cannot gather any extra heat when the sun stops shining. I That's more, some of its stores seep up into the air and get lost. During the night, the earth always loses a lot of the heat it gathered during the day.

But summer nights are short and when morning comes there is still some left. So the heat stored in the ground builds up day by day. You would expect the hottest days to be in late June, when the days are longest. Instead they come in July and August. This is because the earth has had time to store up enough heat to warm the weather. Things change when the nights grow longer than the days. In winter, the earth loses its day's warmth soon after the sun sets and before it rises again, the world shivers with cold.