Welcome to You Ask Andy

David Fisher, age 10, of Tulsa, Okla., for his question:

HOW WERE TIME ZONE BOUNDARIES SET?

The first people on earth to keep time probably were those who counted such natural repeating events as the rotation of star constellations in the sky, sunrises and sunsets and changes of seasons. After a time the pattern of regularity of natural events could be seen. As soon as man began to keep count, he began to measure time.

Clocks in various parts of the world at a given hour do not show the same time. When it is 12 noon in your city, it isn't also 12 noon across the nation.

It is midnight at a spot on the other side of the world when it is 12 noon in your city. Every place on earth, both east and west of where you are living, has a different time. Twenty four different time zones around the world, with clocks set properly, make it possible for the sun to be approximately overhead when 12 noon comes around on the clock each day.

The United States and Canada lie within eight standard time zones. Each zone is one hour different from its neighboring zone. The zones are earlier in the west and later in the east. The boundaries between the zones are irregular so that neighboring communities can have the same time.

As the last century drew to a close there were about 100 different times in the United States. They were called railroad times because they were tied into various railroad schedules. They were standardized into four standard time zones in 1883.

Each time zone around the world is centered on a meridian of longitude 15 degrees apart. In Canada and the United States, the Eastern Time Zone is centered on the 75 degree west meridian while the Central Time Zone is found on 90 degrees west. The Mountain Time Zone is centered on the 105 degree west meridian and the Pacific Time Zone is on the 120 degree west meridian.

As the time zone boundaries cross the nation, they are very irregular so that places near the edge of a zone can have the same time as neighboring communities.

Central meridians of other North American time zones are 60 degrees west for the Atlantic Time Zone, 135 degrees west for the Yukon Time Zone and 750 degrees west for the Alaska Hawaii Time Zone. Western Alaska uses Bering Standard Time, which is centered on the 165 degrees west Meridian.

Worldwide time zones were established in 1884. The meridian of longitude passing through the Greenwich Observatory in England was chosen as the starting point for the world's time zones. Twelve time zones are located west of Greenwich and 12 to the east.

Halfway around the world from Greenwich is the International Date Line. A traveler crossing this line while heading west, toward China, loses a day. If he crosses it traveling eastward, he gains a day.

 

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