Andrew Gyure, age 10, of Omaha, Nebraska, for his question:
Why do we have time zones?
The time zones do a rather shaggy job of dividing the globe into 24 sections. They are related to the longitudes that do such a neat job of sectioning the globe with perfectly straight lines, running from pole to pole. There are, however, 360 half¬ circles of longitude, 15 times more than the time zones. Naturally there is a reason for this and also a reason why the time zones zig and zag while the longitudes do not.
As our round world rotates toward the east, the sun rises above the eastern horizon and appears to march westward up and over the sky. As it passes, it takes the time of day along with it and the moment of noon marks the highest point it reaches in the sky. This is how things are in a spinning globe and its rotation is related to the time it takes for the sun to cross the sky. Also remember that the round globe has another side and the same daily routine goes on there, too.
Through each calendar day, as the earth rotates through day and night, the sun appears to complete a circle around the entire globe. It never pauses, even to mark the moment of high noon. Actually, its high noon point is on its way westward around the globe. This means that it arrived earlier in the places east of you and the people living to the west of Omaha must wait for their midday until later. At noon in Omaha, it is midnight in the Himalayas on the far side of the world. It takes the sun about four hours to cross from New England to California.
It seems logical to base our daily routines on morning and afternoon schedules, but the sun carries this time system around the world. The time zones were invented to tag this global whirligig. It would be a nuisance for travelers to change their clocks every minute to keep pace with the moving sun. So 24 time zones were made, on change for each hour of the day.
The longitudes meet at the poles, the two ends of the axis around which the earth rotates. This is why the sun appears to cross them on its westward circuit. Every hour it crosses 15 of our 360 longitude degrees. So each time zone is 15 degrees wide, more or less. However, we had to invent a starting line for the 24 hour circuit. It was decided to mark this with the prime meridian. This is Longitude 0 degrees, the half circle that runs through the time keeping observatory at Greenwich, England.
Based on Greenwich Time, the prime meridian marks the moment of noon. The time zones to the east of this line are each one hour later and those to the west are each one hour earlier. The east and west time meridians meet halfway around the globe in the mid Pacific. The 180th meridian is the Date Line that marks the end of the calendar day and the birth of the next one.
The time zones help stay at homes when making long distance telephone calls to friends in the east or west. But each zone marks the same hour from pole to pole. Their north south dividing lines zig zag to avoid slicing island groups and dense populations. It would be very inconvenient, for example, to divide a city so that westside clocks were one hour behind its eastside clocks.