Time zones are relatively new phenomena in world history. Prior to the late 19th century, the authoritative source for the official time of day was the town clock. At noon each day, when the sun reached the highest point in the sky, clocks could be set and checked. This system worked well in a world where people rarely traveled more than 20 miles from the place of their birth. Even for those who traveled great distances, it didn’t matter a great deal if the time at one’s destination was off from the time at the origin.

This all changed with the advent of railroads. Not only did trains afford faster transportation, but their efficient operation depended upon a standardized method of determining the time. This necessity was the mother of time zones. Take a few moments in the time zone of your choice to learn about the practice that governs the world’s clocks.

Time Zones Started Because of a Missed Train.

In 1878, Sir Sandford Fleming was indignant because he missed a train. Missing trains was not uncommon — particularly because train schedules relied upon the time in whatever locality a train happened to be. The problem was that the clocks in two adjacent towns might differ by anywhere from 2 minutes to half an hour. Fleming proposed a uniform way of determining the time. He divided the earth into twenty-four time zones, each spaced 15 degrees of longitude apart. Since the earth rotates once every 24 hours and there are 360 degrees of longitude, each hour the earth rotates one-twenty-fourth of a circle or 15 degrees of longitude. Sir Fleming’s time zones were heralded as a brilliant solution to a chaotic problem worldwide.

The United States and the Day of Two Noons.

The United States adopted four standard time zones in 1883 at the insistence of the railroad companies. November 18, 1883, was the day everyone was expected to reset their clocks at noon for that particular time zone. It was known as the Day of Two Noons. Read this New York Times article about how this affected life in New York City.

Though most U.S. states began to adhere to the Pacific, Mountain, Central, and Eastern time zones by 1895, Congress didn’t make the use of these time zones mandatory until the Standard Time Act of 1918.

The Rest of the World Joins In.

After less than a year of using the time zone system in the United States, the other countries were quick to see the benefits. In 1884, Washington, D.C. hosted the International Prime Meridian Conference. The conference selected the longitude of Greenwich, England as zero degrees longitude and established the 24 time zones based on the prime meridian. Although the time zones had been established, not all countries switched immediately.

Classification of the Time Zones.

The official name of the time zone classification system is Universal Time Coordinated (UTC). With Greenwich, England established as the starting point, its time zone is, officially, UTC+0. The “zero” is shortened to “Z” or “Zulu.” The aviation industry is one example of several institutions that do not mess around with time zones and officially use one standard time: Zulu time. When a pilot gets a weather report, he or she is told the weather, at a time, with “Zulu” added to the time. The pilot then knows that weather was reported when it was that time in Greenwich and can make appropriate adjustments, if necessary, by adding or subtracting how many hours his or her time zone is offset from UTC+0.

What About the Poles and Outer Space?

Scientists working at the North and South Poles simply use Zulu time. Otherwise, Antarctica would be divided into 24 very thin time zones. Astronauts also use Zulu time, otherwise, those on the International Space Station would have to adjust their clocks every 3.75 minutes as they pass over one time zone to another.

Each Country Chooses How to Divide Its Time Zones.

While the United States divides itself more-or-less equally by time zones, not all countries follow the same practice. The world’s most populous country, China, for example, is all in one time zone.

The country with the most time zones will probably surprise you. It is France. (Read why this is true.)

Spring Ahead, Fall Back.

Some parts of the world observe Daylight Saving Time, where clocks are moved ahead one hour in the spring and back an hour in autumn. This tends to be observed more in countries more distant from the Equator. The closer one gets to the Equator, the less variance there is in the amount of daylight from season to season. (Read how Daylight Saving Time was proposed as a joke by Benjamin Franklin.)

The Island of Two Times.

Märket, an 8.2-acre island in the Baltic, is divided between Sweden and Finland – and consequently uses two time zones. What do the residents think about this? That question is moot because the island is uninhabited.

You May Have to Adjust Your Watch By More than 60 Minutes.

Generally, when you drive from one time zone to another, you only have to adjust your watch by 60 minutes, one way or the other. That is not always the case. If you go to Afghanistan from China, you will have to adjust your watch by 3 hours and 30 minutes. If you go from China to Pakistan, the adjustment is 3 hours.

A World of Variety in the World’s Time Zones.

Of the 37 time zones, there are 7 that are offset by 30 minutes from the norm:

• UTC +10:30 — Lord Howe Island/Australia
• UTC +9:30 — some regions of Australia
• UTC +6:30 — Myanmar and Cocos Islands
• UTC +5:30 — India and Sri Lanka
• UTC +4:30 — Iran and Afghanistan
• UTC -2:30 — Newfoundland and Labrador/Canada
• UTC -9:30 — Marquesas Islands/French Polynesia

Three are offset by 15 or 45 minutes from the standard:

• UTC +12:45 — Chatham Islands/New Zealand
• UTC +8:45 — Western Australia/Australia
• UTC +5:45 — Nepal

Read about how scientists measure and describe one second.

Read more fun facts about time.