Set Your Watches! Kids' Guide to Time Zones

Icon May 23, 2021 1:02 PM

Have you ever noticed while watching television that when a commercial promotes a new episode, they mention different time zones? That's because Earth is divided into 24 different regions that each have a different time. These regions are separated by longitude lines that are roughly 15 degrees apart. So depending on which way you travel, time moves forward or back an hour for each 15 degrees of longitude that you go through.

Why Are Time Zones Used?

We have time zones because it wouldn't make sense for it to be the same time everywhere in the world at once. If that was the case, noon might be in the sunniest part of the day for some people but at bedtime or early in the morning for others. Since the sun strikes different parts of the planet at different times, it makes sense to have time zones so that the sun always sets when your clock says it's nighttime and rises when your clock says it's morning.

Time zones are generally separated by longitude lines every 15 degrees. However, it isn't a perfect fit; sometimes, the borders of time zones are moved to align with international boundaries instead of rigidly adhering to the longitude rule. It would be confusing for everybody if the next town over was in a completely different time zone, especially in a small country!

How Many Time Zones Are There?

There are 24 time zones around the world because there are 24 hours in a day. There are 360 degrees of longitude around the globe. Dividing 360 by 24 gives you 15 degrees of longitude, which is why time zones are roughly 15 degrees wide.

A Historical Timeline of Time Zones

In the 1700s, an English clock-maker named John Harrison figured out that you could use a clock with to calculate a ship's longitude at sea. He invented a device called a marine chronometer, which could be used to calculate the difference between the observed local time and the time at Greenwich, England (Greenwich Mean Time). This could then be used to determine the ship's longitude. His work connecting time with longitude led to great improvements in marine navigation and safety.

However, many cities around the world still based their clocks based on when the sun rose and set until the American railroads became a commonly used mode of transportation. Train travel could be challenging and even dangerous because every station set its own time; it was difficult to set train schedules and keep multiple trains running over the same tracks safely without consistent clocks. This led to the U.S. adopting four standard time zones in 1883. In the years that followed, the prime meridian was designated as the line of longitude running through Greenwich, England, and global time zones would be calculated from there.

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