earthglobe.app

Time zones explained: a globe lesson

A student has a cousin in another country and asks why the cousin is always asleep when they want to call. This lesson answers that question with a globe that shows where the Sun is shining right now. Students see that the Earth turns, that the Sun can only light half of it at a time, and that clocks are set so that noon is roughly when the Sun is highest.

Suggested age: 9–13 · Time: about 40 minutes · Links: all lessons · for schools

Learning goals

By the end of the lesson students can:

  1. Explain that it is day on the half of the Earth facing the Sun and night on the other half.
  2. Explain that the Earth turns once in about 24 hours, so it turns about 15 degrees each hour.
  3. Work out the time in another country from its difference from UTC (the world's reference time).
  4. Give one reason why time zone borders are not straight lines.

What you need

Step-by-step globe activity

  1. Start with a guess (3 min). Ask: "Is it daytime everywhere in the world right now?" Take a show of hands.
  2. Show day and night now (5 min). Open the globe in Satellite mode. Point out the soft line between the lit half and the dark half. Explain that this line is worked out from the current time, so it matches the real Sun at this moment. Turn the globe so the class can see both sides.
  3. Find home (3 min). Type your town or country into the search box and press Go. Is it on the day side or the night side? Does that match what students see out of the window?
  4. Visit four cities (8 min). Search for Tokyo, New York, London and Sydney one at a time. For each one, students say "day" or "night" and write it in a table. Ask: "Where would you not phone a friend right now?"
  5. Turn the Earth by hand (5 min). Let a student drag the globe slowly from west to east (left to right on the screen when north is up). Explain that the real Earth turns this way once in about 24 hours. A full circle is 360 degrees, so each hour the Earth turns about 15 degrees. That is why places about 15 degrees apart (east to west) have clocks about one hour apart.
  6. Look at two unusual countries (8 min).
    • Tap China. Its card shows how big it is. China stretches far from east to west but uses one clock time (UTC+8) for the whole country. Ask: "What would sunrise be like in the far west?" (Later in the morning by the clock than in the east.)
    • Tap India, then Nepal. India is 5 hours 30 minutes ahead of UTC and Nepal is 5 hours 45 minutes ahead. Not every zone is a whole number of hours.
  7. Show the zones (5 min). Tell students that the world uses 38 different clock offsets, from 12 hours behind UTC to 14 hours ahead, and that the borders mostly follow countries rather than straight lines.
  8. Wrap up (3 min). Back to the opening question: "Is it daytime everywhere?" Students explain the answer in one sentence each.

Why time zones are not straight lines

In a perfect system every zone would be a strip 15 degrees wide, one hour apart. Real zones follow borders, because people in one country or region want to share the same clock. Some large countries choose one zone (China), others use many (Russia has 11). Some places use half-hour or 45-minute offsets, and many countries move their clocks one hour forward in summer (daylight saving time). That is why a real time zone map looks jagged.

Questions for students

  1. Why is it night in some countries while it is day in yours?
  2. The Earth turns 360 degrees in about 24 hours. About how many degrees does it turn in one hour?
  3. When it is 12:00 UTC, what time is it in Tokyo (UTC+9)?
  4. When it is 09:00 UTC, what time is it in India (UTC+5:30)? And in Nepal (UTC+5:45)?
  5. China is very wide but uses one time zone. Give one good thing and one problem about that.
  6. Why don't time zone borders follow straight lines?

Answer key (for the teacher)

  1. The Earth is a ball, so the Sun can only light the half that faces it. The other half is in shadow, which is night. As the Earth turns, places move from the night side into the day side.
  2. About 15 degrees (360 ÷ 24 = 15).
  3. 21:00 (9 pm). 12 + 9 = 21.
  4. India: 14:30. Nepal: 14:45.
  5. Good: everyone in the country shares the same clock, which makes trains, TV and business simpler. Problem: in the far west the Sun is high in the sky much later by the clock; solar noon can be as late as about 15:00 there.
  6. Zones mostly follow country and regional borders so that people who work and travel together share one time. Some countries also pick a zone for practical reasons, and some use daylight saving time in summer.

Optional extension

Plan a video call. In pairs, students pick a city on another continent, find it on the globe, and look up its UTC offset. They find a time between 08:00 and 20:00 in both places when a class could talk. They then check on the globe whether both cities would be in daylight at that time today. For older students, add daylight saving time: what changes in summer?

Frequently asked questions

How many time zones are there?

It depends on how you count. A simple model has 24 one-hour zones, each 15 degrees wide. In real life the world uses 38 different offsets from UTC, from UTC−12 to UTC+14, because some places use half-hours or 45 minutes.

What is UTC?

Coordinated Universal Time, the reference time the world's clocks are set against. A place that is "UTC+2" is two hours ahead of it.

Do big countries have many time zones?

Some do and some do not. Russia uses 11 time zones, while China uses just one for the whole country.

Can you see the time zones on earthglobe.app?

You can see the live line between day and night, which is what time zones are built around. Teacher mode has a time zone layer with the 24 one-hour zones of the simple model; it does not show the real borders.