Time to Get in the Zone

Contributor: Lindsey Congalosi. Lesson ID: 13119

Why do we have time zones? Wouldn't it be easier if everyone used the same time zone? NO! Read more to find out why.


Earth Science, World

learning style
Auditory, Visual
personality style
Otter, Beaver
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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  • Did you know that you can have two birthdays?
  • Or skip a day entirely?

You can even go back in time to yesterday.

  • How can this be possible?!

Read on to find out.

Time Zones

The earth is divided into roughly 24 time zones. People all over the planet are experiencing a different time of day.

As the saying goes, it's 5:00 somewhere. And four o'clock, three, and all the other times!

world map with time zones

  • Why do we use a system that complicates things?

Time differences cause many issues, from the scheduling of national events to jet lag.

  • So why do it?

Look at this Day and Night World Map, showing where daylight is occurring at this exact moment.

The light-colored area is where daylight is happening, and the dark-colored areas are nighttime. The shades of grey represent sunrise or sunset.

Now imagine that everyone on the map was experiencing the same time of day — noon. The people toward the center of the lighted part are in the middle of their day, so that would make sense.

  • However, what about the people in the dark or the shades of grey?

These people would be experiencing noon at a new time of day, which makes much less sense.

The contiguous United States consists of four separate time zones.

Map of the US Timezones post-2007

These time zones are named Eastern, Central, Mountain, and Pacific from east to west. You may have seen some of these zones on commercials for television shows or events.

For example, the Super Bowl is the National Football League championship game. When kickoff happens, people on the country's east coast see it at 6:30 pm, while those on the west coast see it at the same time, which is 3:30 pm.

If you live in Hawaii, you'd be tuning in at 1:30 pm. In Bangkok, Thailand, you must watch the live game at 6:30 am to see the beginning.

A new time zone begins every 15° longitude.

time zones

The earth is a sphere and, therefore, 360° around. The earth makes one rotation every 24 hours. If we divide 360 degrees by 24 hours, we get 15°. The earth rotates 15° per hour.

However, as you can see from the time zone outlines below, it's not always 15 degrees.

map of actual time zones

Some time zone boundaries have been adjusted so that cities or small countries are not cut in half, and other time zone boundaries are entirely ignored by countries who refuse to follow the system. In the Go! section, we'll return to this.

Time zones are not only named but numbered. If you Google what is my time zone, you'll see GMT and then a positive or negative number.

For example, Eastern Standard Time is also called GMT-5. Move one time zone to the west, and you're in Central Standard Time or GMT-6.

GMT stands for Greenwich Mean Time. Greenwich is an essential city in England for several reasons.

Greenwich is located at 0° longitude. Unlike latitude, longitude has no clear beginning, middle, or end.

The line of longitude passing through Greenwich was established in the mid-1800s when it was first used as a reference point for ocean navigation. Ships would track their distance from the prime meridian to help them find their way.

Greenwich, England

As technology advanced and railway travel became more common, people became less geographically isolated, and the need for a standard system of time developed. Before this, towns and cities determined their times based on the movement of the sun, called local solar time.

Since Greenwich was already the 'starting point' of longitude, known as the home of the prime meridian, and England was a highly influential world power, it was determined that Greenwich would be the starting point for time as well.

Prime Meridian location in Greenwich

  • Back to today; remember the GMT number you saw earlier?

GMT stands for Greenwich Mean Time. The number after this refers to the difference in time relative to Greenwich, England.

Eastern Standard Time is GMT-5, meaning that the eastern portion of the US is five hours behind Greenwich.

Travel in the other direction from Greenwich, and you'll see positive GMT numbers. Paris, France, follows Central European Standard Time or GMT+1, one hour ahead of Greenwich.

  • Need a quick refresher?

Watch the following video.

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Changing Days

  • What happens at the 'end' if the prime meridian is the 'beginning' line of longitude?

If you traveled from the Prime Meridian to the opposite side of the globe, you would reach a longitude of 180°. This line is also called the International Date Line.

map showing the International Date Line

This line marks where one day begins and another one ends. To find out how that works, watch the video below.

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Everyone experiences the same date between 11:00 pm and midnight.

Imagine that you live on the International Dateline (although it runs through the middle of the Pacific Ocean, so very few people actually do), and it's Christmas Eve. When it is 11:45 pm for you, Christmas Eve is almost over. At midnight, Merry Christmas!

But only for you and anyone else in that time zone. The rest of the world is still experiencing Christmas Eve and won't see December 25th for another 1 to 23 hours.

  • How do you use this information to get two birthdays?

You should start your birthday celebration in Samoa, GMT+13.

Samoan Islands

The following day, you would fly to neighboring American Samoa, GMT-11 (about 30 miles away), crossing the International Date Line and landing on your birthday again!

If you wanted to miss a day, you could repeat this process in reverse.

Watch the video below for a more thorough explanation of this oddity.

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  • Have you started to understand how time zones work?

Watch one more video if you need a quick review of what you've just learned.

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Now, move to the Got It? section to see how to use this new knowledge.

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