Sherry Mahler, age 11, of Tucson, Arizona, for her question:

How can the sun stay up until 10 o'clock in Ireland?

In Arizona, the sun always goes to bed at a respectable time. In Ireland, it stays up until 10 o'clock and maybe later, but only in the summer time. In winter, the Irish days are much shorter than those in Arizona. The sun gets up later and retires much earlier. These variations occur because Ireland is about 1,400 miles farther north than Arizona    and the earth's axis is tilted to make a seasonal difference in the days.

In summer, the North Pole end of the axis bows toward the sun. As the earth turns, the entire Arctic circle remains bathed in daylight and the summer sun does not set at all for weeks. Farther south from the pole, it dips below the horizon and rises again in a few hours. Northern latitudes enjoy very long summer days and short summer nights, as they do in Ireland. But Arizona is very much farther south and as we get closer to the equator, the d;.y~ and nights are more nearly equal throughout the year.