Why Do We Have Different Time Zones? (2024)

Quick, find the nearest clock. What time is it where you are? Have you ever traveled to another place and experienced a time change? Maybe you know someone who lives far away and is a few hours ahead of you. How is that possible? Is it time travel? Of course not! They just live in a different time zone.

To understand time zones, start by thinking about the shape of the Earth. You know our planet is a sphere that spins on an imaginary pole called its axis. Every 24 hours, the Earth makes a complete rotation. We call each full turn a day.

Imagine shining a flashlight at a globe. Only part of it would receive light. The opposite side would be dark. As Earth rotates, different parts of Earth receive sunlight or darkness, giving us day and night. As your location on Earth rotates into sunlight, you see the sun rise. When your location rotates out of sunlight, you see the sun set.

Imagine if the entire Earth had a single time zone. Noon would be the middle of the day in some places, but it would be morning, evening, and the middle of the night in others. Since different parts of Earth enter and exit daylight at different times, we need different time zones.

People have lived in different time zones for a long time, but it hasn’t always been as organized as it is today. Just over a century ago, towns and cities set their own time. One person would make sure the official town clock read noon when the sun was highest in the sky each day. Then, they would go around town and adjust other people’s clocks to make sure they matched.

As the world became more connected, this grew complicated. Especially as people began to travel across North America by train, the many time zones became difficult to follow. At one point, train stations in the United States alone had to keep up with 75 time zones across the country.

In the late 1800s, a group of scientists came up with a new system for time zones. They called it standard time. To build the time zone map, they studied Earth’s movements.

As Earth rotates on its axis, it moves about 15 degrees every 60 minutes. After 24 hours, it has completed a full rotation of 360 degrees. The scientists used this information to divide the planet into 24 sections or time zones. Each time zone is 15 degrees of longitude wide.

Distance between the zones is greatest at the equator. It shrinks to zero at the poles because of the curvature of Earth. Since the equator is about 24,902 miles long, the distance between time zones at the equator is approximately 1,038 miles.

The imaginary dividing lines begin at Greenwich, a suburb of London. The primary dividing line of longitude is called the prime meridian. Longitude is the angular distance between a point on any meridian and the prime meridian at Greenwich.

The time at Greenwich is called Greenwich Mean Time (GMT). As you move west from Greenwich, every 15-degree section or time zone is an hour earlier than GMT, while each time zone to the east is an hour later.

Not everyone accepted the idea of standard time right away. In fact, many countries continue to set their own times today. For example, in China, it’s always the same time all across the country. That’s despite the fact that China stretches across three standard time zones. Other nations adopted systems that change time zones by smaller increments, like 15 or 30 minutes. For that reason, there are more time zones than the standard 24 in use today.

Having different time zones means that no matter where you live on the planet, your noon is the middle of the day when the sun is highest, while midnight is the middle of the night. Let’s take a closer look at how this works.

Let’s say you live in Charlotte, North Carolina, and you have a cousin who lives in Madrid, Spain. Charlotte is five time zones to the west of Greenwich, which is written as GMT -5. Madrid is 1 section east of Greenwich (GMT +1). This means Charlotte and Madrid are six time zones apart.

When your cousin is eating lunch at noon Madrid time, you are probably just getting out of bed to get ready for school. This is because at 12:00 p.m. in Madrid, it’s only 6:00 a.m. in Charlotte. On the other hand, if you wanted to chat with your cousin online after dinner at 6:00 p.m., it would already be midnight in Madrid!

Time zones are further complicated by Daylight Savings Time, which is observed by some countries and not others. Have you ever been surprised by a time change? There’s certainly a lot to keep up with!