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, and three, and all the other times as well!

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?

Take a look at TimeandDate.com's Day and Night World Map. The large map at the top of the page is showing where daylight is occurring at this exact moment.

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

Now imagine that everyone on the map was experiencing the exact same time of day - let's say noon (12 pm). The people towards the center of the lighted part are in the middle of their day, so noon would make sense for them.

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

These people would be experiencing 12 pm at a new time of day, one that makes much less sense.

The contiguous United States consists of four separate time zones:

US timezone map

Image by National Atlas of the United States, via Wikimedia Commons, is in the public domain.

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

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

If you live in Hawaii, you'd be tuning in around 1:30 pm. If you happen to be in Bangkok, Thailand, you would have to watch at 6:30 am in order to see the beginning of the live game.

A new time zone begins every 15° longitude.

time zones

Earth is a sphere and, therefore, 360° around. Earth makes one rotation every 24 hours. If we divide 360 degrees by 24 hours, we get 15°. 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 ignored completely by countries who refuse to follow the system. We'll come back to this in the Go! section.

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 important 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 become more common; people became less geographically isolated, and the need for a standard system of time developed. Before this, towns and cities determined their own 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 the present day; 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 Why do we have different time zones? from It's AumSum Time.

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Changing Days

  • If the prime meridian is the ‘beginning' line of longitude, what happens at the ‘end'?

If you were to travel 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 the International Date Line Works, watch this video by shepdi:

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Between 11:00 pm and midnight (12:00 am), everyone on Earth is experiencing the same date.

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.

  • So how do you use this information to get two birthdays?

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

Samoan Islands

The next morning, 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 just repeat this process in reverse.

Watch The longest day ever | The international date line by Maddie Moate to get a more thorough explanation of this oddity:

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  • Have you started to understand how time zones work?

If you need a quick review of what you've just learned, watch Geography Lesson: Time Zones Explained | TWIG from TWIG Education:

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

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