Gary Jones, age 13, of Peterborough, Ontario, Canada, for his question:

Why does the Date Line zip and zap?

This, of course, refers to the International Date Line that divides one calendar day from the next. The spinning earth takes about 24 hours to turn the opposite side of the globe to face the sun. It rotates around in a smooth unbroken operation, hence, there is no natural division between one day and the next. The Date Line and the 24 time zones are man made inventions.

Suppose the International Date Line ran plumb down the middle of Peterborough, Ontario. Right noon, the people living on the west side of the line would be enjoying the relaxation that usually goes with Saturday. Meanwhile the people on the east side of the line would be toiling, through Friday to complete their work a day week. Tomorrow, things would be even more inconvenient. Half the town would be resting up on Sunday, while the other half lags behind through Saturday.

This is the sort of problem that the International Date Line tries to avoid. And to do so, it must zig and zaR around populated places so that neighbors are not divided by the days of the calendar. The world, of course, is densely populated and getting more so. However, so far human population has not occupied the oceans. And the Pacific provides vast uninhabited expanses where it is not necessary for neighbors to leap between Monday to Tuesday when they cross the street. This is one reason why longitude 180 degrees seemed a logical place to place the man made marker that divides one calendar day from the next.

This meridian half circle runs from pole to pole, marking the midnight where yesterday ends and tomorrow is born. It happens to be the opposite half of the Prime Meridian that runs through Greenwich, England, which marks the exact midday of Universal Time. The mid Pacific is a vast expanse of ocean, but nothing, is 100 per cent perfect. Latitude 180 cuts through a few populated land areas and brushes close by several island groups.

Since the marker is man made, adjusting it to suit everybody's convenience was no big problem. In the Arctic Ocean, it bends eastward from the 180th meridian and jogs through the Bering Strait for the convenience of the Alaskans and their Siberian neighbors. The Alaskans enjoy Sunday while the Asians are back to work on Monday.

Some of the Aleutian Islands are west of the 180th meridian. So the line jogs westward to include them with the Alaska mainland. South of the equator, the line bends eastward around most of the Samoa Islands and avoids slicing through the group of Fiji Islands. It remains on the east side of the meridian to include some offshore islands in the date zone of New Zealand.

Hardly anybody lives on the zig zapginp line that divides one calendar day from the next. But the dramatic event certainly is noticed by global travelers. Since the earth rotates eastward, the west side of the line is a day ahead of the eastside. Traveling westward across the Date Line, the calendar leaps ahead to tomorrow. Traveling, eastward the calendar drops back a day    say from Sunday to Saturday.