As we know from previous lessons lines of longitude also known as meridians run from north to south across the globe and meet at the North and South Poles. The starting point for this system (0°) is Greenwich meridian in England. Locations west of this line have a longitude of 179° west; those to the east have a longitude of up to 179°east. The 180th meridian is exactly on the opposite side of the globe, in the middle of the Pacific Ocean and it is known as the International Date Line.

Have you ever travelled to another place and experienced time change? Maybe you know someone who lives far away and is a few hours ahead of you. How is that possible?

If the whole Earth had a single time noon would be in 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 the Earth enter and exit daylight at different times, we need different time zones.
Watch the following short video clip which explains why time zones are necessary.

As Earth rotates on its axis, it moves about 15 degrees every 60 minutes. Thus after 24 hours, it has completes a full rotation of 360 degrees. As a result of this scientists divided the Earth into 24 different sections known as time zones. Each time zone is 15 degrees of longitude wide. The starting point for these time zones is the prime meridian in Greenwich, also called Greenwich Mean Time (GMT). As can be seen from the map below as one moves west of Greenwich, every time zone is an hour earlier than GMT, while each time zone to the east is an hour later.

Let us say you live in Malta, and you have a friend who lives in Tokyo, Japan. Malta is one time zone to east of Greenwich, which is written as GMT+1. Tokyo is 9 sections east of Greenwich (GMT+9). This means that Malta and Tokyo are eight time zones apart. Thus if the time in Malta is 11:00 AM it is 7:00 PM in Tokyo.

As explained, the world time zone map shows the division of the world into 24 time zones of 15 degrees longitude each. However, if you compare this theoretical system with actual time usage throughout the world, you will see there are many variations in how countries actually observe time zones. The reason for this vary but include commerce and transportation.

• Now say if the following statements are true or false. Rewrite correctly the false statements.
– The zero degree longitude is known as the equator.
– The Prime Meridian passes through Greenwich in London.
– The Prime Meridian not only divides the eastern from the western hemisphere, but it is also where longitude and time is measured from.
– In 1884 most nations agreed to standardise time and that Rome would be where all time is measured from.
– Time at the Greenwich meridian is known as Greenwich Mean Time (GMT) or Universal Time (UT).

• Now log on to the website https://24timezones.com/timezone-map#gref

It shows an interactive map of the world divided into time zones. There are 24 different time zones. They are separated by one-hour intervals and there is a new time zone roughly every 15 degrees of longitude. The zones are measured in hours ahead of or behind Greenwich Mean Time, or GMT, which is the time at the Prime Meridian Line.

Remember that because the earth rotates from west to east, the hours grow earlier from east to west. When it is 3:00 p.m. in Moscow, it is noon in London. To determine the standard time for any time zone in the world, add one hour for each time zone each of Greenwich. Subtract one hour for each time zone counted in a westerly direction from Greenwich.

• Now answer the following questions:
a. Name another country that has the same time zone as the UK.
b. Name four countries that are 3 hours ahead of GMT.
c. Which of the following countries are 6 hours behind of GMT. Tick the correct countries?

Brazil         Iceland           Peru           Russia          Columbia        Kuwait          East Canada         Australia         East USA

d. Name one country that is 8 hours ahead of Greenwich.
e. Why do you think that China is not divided into different time zones?
f. Use the map to calculate the time in the following places when it is noon at Greenwich.

Valletta (Malta)       Moscow (Russia)         Beijing (China)         Reykjavik (Iceland)

g. If it is midnight in Greenwich what is the time in Brasilia the capital of Brazil?
h. If the time in London is 2:00 p.m. calculate the time in

Saudi Arabia         New Zealand          Iceland        South Africa         Portugal