Why are there time zones at all?

Because the Earth turns, so the Sun is overhead in different places at different times. Midday ought to be when the Sun is highest, and it cannot be midday everywhere at once. The world is divided into zones roughly fifteen degrees of longitude wide, because the Earth turns fifteen degrees every hour.

Are these the real times?

They are the standard offsets from Greenwich Mean Time, which is what a lesson on time zones needs. They are not the time right now: this board never reads a clock, so the hour is whatever you set it to. Summer time is not shown either, and it moves half the world's clocks forward by an hour for part of the year.

Do time zones really follow the lines of longitude?

Roughly, and the exceptions are interesting. Zones bend round national borders, because a country with two times in it is inconvenient: China keeps a single time zone across five zones' worth of longitude, India is half an hour out of step, and Nepal is three quarters of an hour out.

What is the International Date Line?

The line down the middle of the Pacific, roughly at 180 degrees, where the date changes. Go west across it and you lose a day, go east and you gain one. It is why this board says the next day or the day before when the sum crosses midnight.

Time Zones

Geography · Year 5–Year 6

Move London's clock, tap a city, and count the hours between.

About the time zones

A world map with a line of longitude every fifteen degrees, because fifteen degrees is one hour. Move London's clock with the steppers, tap one of eight cities, and the board reads both clocks and washes the hours in between so a class can count them.

The counting is the point. Tap Tokyo and nine strips light up and are numbered one to nine, so nine hours is something a class works out from the picture rather than a number the board announces. Delhi is there for the same reason from the other end: its wash is five strips and a narrow one, because India is half an hour out of step with the meridians.

The day changes when it should. Eleven at night in London is nine in the morning in Sydney, the next day, and a board that showed 09:00 with nothing to say which day it was would be teaching the mistake this tool exists for. The day and the hour come out of the same sum.

These are the standard offsets from GMT. Real time zones bend round borders rather than following the meridians: China keeps one time zone across five of them, India is half an hour out, and half the world puts its clocks forward in summer, so British Summer Time is an hour ahead of what this board shows from late March to late October. Nothing here claims to be the time now.

Latitude and Longitude is the tool for reading a position off the same map, and Lines of the Globe is where the prime meridian sits on a ball.

How to use it on your whiteboard

1Tap a city to see what time it is there.
2Tap Earlier or Later to move London's clock an hour at a time.
3Count the numbered strips between Greenwich and the city: each one is an hour.
4Tap Midday to put London's clock back to 12:00.

Questions

Why are there time zones at all?: Because the Earth turns, so the Sun is overhead in different places at different times. Midday ought to be when the Sun is highest, and it cannot be midday everywhere at once. The world is divided into zones roughly fifteen degrees of longitude wide, because the Earth turns fifteen degrees every hour.
Are these the real times?: They are the standard offsets from Greenwich Mean Time, which is what a lesson on time zones needs. They are not the time right now: this board never reads a clock, so the hour is whatever you set it to. Summer time is not shown either, and it moves half the world's clocks forward by an hour for part of the year.
Do time zones really follow the lines of longitude?: Roughly, and the exceptions are interesting. Zones bend round national borders, because a country with two times in it is inconvenient: China keeps a single time zone across five zones' worth of longitude, India is half an hour out of step, and Nepal is three quarters of an hour out.
What is the International Date Line?: The line down the middle of the Pacific, roughly at 180 degrees, where the date changes. Go west across it and you lose a day, go east and you gain one. It is why this board says the next day or the day before when the sum crosses midnight.