Lesson video

Hello, my name is Mrs. Galava, and I'm so happy that you're joining me to do some geography today.

From our unit on time zones, can we time travel on planet Earth today? Our lesson is called the International Dateline and Time.

By the end of today's lesson, you'll be able to use time and date maps and the international dateline to explore time zones around the world.

Now some of the learning may be a bit tricky, might be a bit new to us today, but it's okay because I'm going to be here the whole way to help you learn.

We've got three key words for our learning today.

So I'll say them first and then I'll give you a chance to say them for your turn.

So the first one, my turn, time zone.

Well done.

Antimeridian.

Great.

And the last one, border.

Brilliant.

Now we'll be finding out about these keywords throughout the lesson, but let's just have a quick look at their meaning.

So a time zone is a region where the same standard time is used.

An antimeridian is the line of longitude opposite a meridian.

Antimeridian forms the basis of the international dateline.

And a border is the dividing line between two countries.

Our lesson is split into two parts today.

Our first part is going be about where does a day begin? To understand where a day begins, we need to look at how we measure time, and where in the world time changes to a new day.

And in our previous lessons we've learned about lines of longitude, which give our position in degrees east or west of the prime meridian.

And these also help us to learn about where new days begin.

Now the prime meridian, which runs through Greenwich in London is located at naught degrees longitude, and places around the world are located at degrees west or degrees east of the prime meridian.

And on the very opposite side of the earth to the prime meridian at 180 degrees is the antimeridian.

And this lies in the middle of the Pacific Ocean and it's where the east and west lines of longitude converge.

They meet at 180 degrees and it's directly opposite the per the prime meridian, which runs through Greenwich.

So if you've got a globe in your classroom, you could have a look and see where that line lies and it runs in a straight line.

It's a line of longitude that runs in a straight line from the North Pole to the South pole.

And the international dateline is also located at 180 degrees east and 180 degrees west of the prime meridian.

And this is the place where the date changes and therefore new days begin.

So we need to remember that location of the antimeridian because it also helps us work out where new days begin and is the basis for the international dateline.

Like we said, while the antimeridian forms the basis for the international dateline, it is not a straight line running completely from the north to the south pole.

You can see on this map that the international dateline does wiggle a bit.

It doesn't follow the straight line of the antimeridian completely from the north to the south poles.

Some of these deviations, these wiggles are to account for national borders, the borders of countries.

Can you spot any places where the international dateline wiggles a bit? Well done.

You can see it wiggles right at the northern hemisphere there and also near the equator.

And the reason for this is to keep whole countries in the same date.

Imagine how confusing it would be if the same country had to cope with two different days.

So half of the country might think it was Sunday and the other half might think it was Monday.

That would be really hard to manage, wouldn't it? We're going have a look at some of these wiggles or deviations in more detail now.

On this map, can you see that the islands of the US state of Hawaii lie almost directly north of the islands of the nation of Kiribati in the Pacific Ocean? So theoretically they should be in the same time zone because they fall within the same lines of longitude.

However, Kiribati is part of the line islands along with Samoa and Tonga.

So the leaders of Kiribati decided to keep Kiribati in the same time zone as the other islands.

As the international daylight marks the start of a new calendar day, it also therefore marks the start of a new year.

And you may know that places all around the world celebrate New Year at different times.

The new day of the new year starts at different times around the world.

Maybe you've seen some of the celebrations on television.

We're going to have a think now about which places will celebrate New Year's Day first.

Do you think it would be the United Kingdom or Australia? Have a think with the person next to you and then we'll have a look together.

Now if the international dateline marks the start of a new day, which places will experience a new day first? Well, because the earth rotates in an anti-clockwise motion, places to the west of the international dateline are the first to experience a new day.

After each full rotation of the earth countries at the edge of the Western hemisphere experience a new day.

Let's have a look at that on our world map.

Here is the international dateline where a new day begins.

And as you can see, all the places directly to the west of the international dateline are the first to experience a new day.

Finally after one full rotation of the earth in 24 hours, places just to the east of the international dateline also experience their new day.

I've got the first check for you today.

I've got Lucas and Izzy who've got two different ideas here.

Lucas says, places to the west of the international dateline are the first to experience a new day and Izzy says, places to the east of the international dateline are the first to experience a new day.

Think about who you think is correct.

Pause the video and we'll come together in a moment to find out.

Well done.

I'm sure you used your learning from this lesson to tell me that Lucas is correct.

Places to the west of the international dateline are the first to experience a new day.

So which places will celebrate New Year's Day first? Well, we learned that it would be places directly to the west of the international dateline.

Therefore the Line Islands, which Kiribati is part of and Samoa and Tonga are in the Pacific Ocean and they're the first places to welcome the new year.

They get a new day and therefore a new year first of all because they are directly west of the international dateline.

Then finally, nearly 24 hours later, American Samoa and Baker Island and Howland Island will also experience their new day and their new year and they are just east of the international dateline.

They will be the last people to celebrate New Year's Day.

Another check for you then.

Which location we'll experience New Year's Day first? Think about what we learned about the international dateline.

Would it be location A, location B, or location C? Have a think and pause the video now.

Well done.

It was that location just west of the international dateline.

So location C would be the first place to experience New Year's Day.

Here's your first task for today, then.

I would like you to use an atlas or a time zone map or a globe to locate these countries, the United Kingdom, New Zealand, Australia, Peru, and India.

Then I'd like you to put them in order based on when they begin their new day, starting with the country that experiences a new day first.

So your list will begin with the country that starts a new day first and then carry on with the country's in order of who experiences their new day next until the last country to experience a new day will be at the end of your list.

Have a go, using all the knowledge that you've learned from this lesson so far, pause the video and we'll come together soon to see how you get on.

I hope you enjoyed having a look at that time zone map and I'm sure that your list looks similar to mine.

And the first place to experience a new day would be New Zealand followed by Australia, then India, the United Kingdom, and finally Peru.

Great job.

We'll move on to the second part of our lesson now.

Now that we know where days begin, we'll have a look at what time it's in different places around the globe.

So this map is showing us the 24 time zones which are based on our longitude meridians.

Those lines that run in straight lines from the north pole to the south pole.

And time zones are designed to guarantee the maximum amount of daylight for people living in each zone.

So why do we need to know what time it is around the globe? When might that be useful? Turn to the person next to you and have a think.

Did you say it might be useful if you want to call family or friends in a different part of the country or if businesses want to talk to each other? There are two ways that it would be useful to know what the time is in different locations.

We also need to know about the time around the world to help international communication.

Like we said, when we want to talk to people in different locations, to help with transport, navigation and businesses.

So it's possible for us to calculate time zones using those lines of longitude.

And when we travel west from the prime meridian, we lose four minutes for every degree of longitude.

And this is because it takes one hour for the earth to turn through 15 degrees.

So 60 minutes, one hour, divided by those 15 degrees means each degree takes four minutes.

So while you don't actually lose any time it's helpful to remember how the time in different time zones is calculated.

Time zones to the west of the prime meridian have a minus or negative sign in front of them to show you that that time is behind the time from the prime meridian.

And then well done, I'm sure you've worked out that time east of the prime meridian, you gain four minutes for every degree of longitude and they've got the plus signs to the east of the prime meridian to show that that time is ahead of time at the prime meridian.

So this means if you know the longitude of a location, then it's possible to calculate the time from the prime meridian.

Now unlike lines of longitude, which are straight, many time zones are not.

Can you see any countries that don't match their geographical time zones? Have a look and pause the video.

Well done.

Did you spot that China should really have had many time zones within it, but it's all just a plus eight hours? Well, many time zones don't follow their meridians exactly to allow for national or state borders.

Let's have a look.

How many time zones does China cover geographically? Well, China should have the plus six hour time zone, plus seven hour time zone, plus eight and plus nine hour time zone.

So it should have multiple time zones within it.

But why might that cause a problem for the people of China if they have four different time zones within the country? Yes, this might make it confusing for people who are working and travelling around the country if the time changed as they moved around the country.

So the country of China has chosen to use UTC plus eight hours for the whole country.

So despite it being a very large country that would normally cover four time zones, the Chinese government decided that the whole country is on the same time as Beijing.

This means that everyone in the country works from the same time, even if they don't receive the same amount of daylight during those hours.

Now, in the United States of America, the time zones don't always follow the meridian lines and this is to allow for some of its state borders rather than national borders so that a whole state within America would stay on the same time zone.

And can you see that there are multiple different time zones within America? And America unlike China has decided to keep multiple time zones within it and typically they try to keep a whole state within the country at within the same time zone.

I've got a check for you.

I'd like you to have a think.

Why do the shapes of some time zones not follow the meridian lines? Think about everything we've learned so far in this lesson.

Pause the video now and we'll come back together shortly.

Well done.

Did you say that some time zones don't follow the meridian lines to allow for national or state boundaries and you might have given the examples of China or the United States of America? Great job.

Your final task for today then.

I would like you to write on the top row of this table where you are in your country and I would like you to write down your current time.

So for me, I might say well, it is 10:00 AM in London as my top line because that's where I'm located and it's 10 o'clock, then I would like you to use a map or an atlas or a globe and find out what the time would be in five other locations around the world in five locations, in different time zones to where you are.

So have fun investigating time zones around the world.

You can pause the video now and we'll come back together to see how you've got on shortly.

I hope you enjoyed having a look at those time zones.

I wonder which locations you chose to investigate.

Here are some examples that I looked at.

So I chose Newcastle.

I said when it's midday in Newcastle, it is 7:00 AM in Orlando, United States of America because they are west of Newcastle.

So they are five hours behind.

It is two o'clock in the morning in Honolulu in America.

It's eight o'clock in the morning in Beijing in China and it's 5:30 in the evening in New Delhi, India.

I hope you enjoyed investigating time zones.

Just to recap our learning for today, the antimeridian forms the basis for the international dateline with some deviations for national borders.

The international dateline is 180 degrees east and 180 degrees west of the prime meridian and is the place where the date changes.

Meridians are the basis for the 24 time zones.

Many do not follow the meridian lines to allow for national or state borders.

West of the prime meridian, you lose four minutes for every degree of longitude and east you gain four minutes for every degree of longitude.

Thank you so much for joining me for this lesson on the international dateline and time, I to see you soon.

Bye.