Time zones

An overview of the division of the world into the imaginary lines of latitude and longitude. The episode explains how the lines of longitude are used to measure time zones around the world.

This video:

  • details how to calculate time in different parts of the world using lines of longitude
  • explains that the Earth rotates about 15 degrees per hour and each line of longitude represents an hour difference counting east or west from the Prime Meridian
  • contains worked examples explaining how to count forward and backwards estimating the time at different locations around the world.

Watch 'Time zones' (2:26).

An overview of the division of the world into the imaginary lines of latitude and longitude.

[Music playing]

[Screen shows a blue sky with clouds. Text on the screen reads, ‘Curriculum Secondary Learners – HSIE. Teaching geographical skills series. Time zones. Presented by Melissa Ellis.’]

Melissa Ellis

I'm sure that you know that at any given moment, time will be different in different parts of the world.

[Presenter is standing in front of a decorative background. In the bottom right-hand corner of the screen, the text reads, ‘Melissa Ellis. HSIE Curriculum Support Project Officer.’]

This is why it's possible to fly from Sydney to LA and arrive the day before. How does that work?

[Next to the presenter, the screen shows an image of a plane’s wing flying above the horizon.]

Let's take a look. The Earth is divided into 24 different time zones by latitude and longitude lines. There is a time zone for every hour of the day.

[Screen shows an image of a world map with grid lines. The Equator is labelled on the horizontal axis and the Prime Meridian is labelled on the vertical axis. Latitude is shown by the horizontal lines and longitude is shown by the vertical lines.]

As we can see here, the time zones run from east to west, each covering about 15 degrees of longitude. This is because the Earth rotates at about 15 degrees per hour.

[On the left of the Equator, the map is labelled, ‘West’. On the right of the Equator, it is labelled, ‘East’.]

All time zones are measured from the Prime Meridian.

Generally, time zones are one hour behind the time zone to the east of the Prime Meridian, and one hour ahead of the time zone to the west of it.

[Screen shows an arrow pointing to the Prime Meridian on the vertical axis of the map. Text on the screen reads, ‘minus 1 hour’ to the east of the Prime Meridian and reads, ‘plus one hour’ to the west.]

So if we know the time at a given location, we can determine what time it is in another part of the world using longitude.

[The screen shows another world map. The map is marked with vertical lines that divide the countries into time zones. Along the bottom of the map, each time zone is labelled a different colour and the colour matches countries that fall within the time zone. Time zones on the east of the Prime Meridian are labelled, ‘plus’. Time zones to the west are labelled, ‘minus’.]

For example, if the time at Prime Meridian is 1 am, what time is it in New South Wales? Because we are counting in an easterly direction, the time is ahead. So it is plus 1, plus 2, plus 3, plus 4, plus 5, plus 6, plus 7, plus 8, plus 9, plus 10, making it 11 am in New South Wales.

[The map on the screen is cropped to only show Europe and part of Africa. As this area is directly east of the Prime Meridian, it is labelled at the bottom with ‘plus 1’. The presenter refers to the labels at the bottom of the page as additional sections of the map are revealed, travelling east, until reaching the time zone in New South Wales. This area is labelled, ‘plus 10’.]

What about the time in Western Australia if we know it is 11 am in New South Wales? Because we are counting back to the east of the time zone, it is 2 hours earlier. So 9 am.

[The screen shows the world map again in full. The map is marked with lines that divide the countries into time zones. Text at the top right of the screen reads, ‘East, 9 am’. Next to the words is a horizontal arrow that points towards the west on the map.]

So there you have it. Happy travels.

[Text on screen reads, ‘References

  • ‘Flying to Los Angeles from Sydney’ by Alex Proimos. CC-BY 2.0.. Accessed at https://commons.wikimedia.org/wiki/File:Flying_to_Los_Angeles_from_Sydney_(3430995956).jpg
  • ‘Prime meridian’ by KMF164. Work in public domain. Accessed at Wikimedia.org/Wikipedia/commons/c/c6/Primemeridian.jpg
  • ‘World time zones’ by Nelo Esteves, Fotographia.CC-BY 2.0. Accessed at https://www.flickr.com/photos/estevesm/473866656/’

Text on screen reads, ‘Acknowledgements. NSW Geography K-10 syllabus © NSW Education Standards Authority (NESA) for and on behalf of the Crown in right of the State of New South Wales 2015. See the NESA website for additional copyright information. NSW Department of Education Curriculum Secondary Learners. Southern Cross School of Distance Education.’

The screen shows an Indigenous artwork. The artwork features a landscape with native Australian animals. It is titled, ‘Our Country’ by Garry Purchase. Text at the top of the screen reads, ‘Filming of these videos has taken place on Bundjalung land.’ Video concludes by displaying the NSW Government logo.]

[End of transcript]

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