Time adventure!

Time helps us say when something happens and how long something lasts.

You woke up this morning. You are reading this now. Later you might eat, play, exercise or sleep. Without time, it would be hard to say when something starts, when it ends and how long you have to wait.

A clock does not make time. A clock measures how much time has passed.

We divide time into smaller pieces.

• 60 seconds = 1 minute
• 60 minutes = 1 hour
• 24 hours = 1 day

A second is very short. Say “one-thousand-and-one” at a calm pace. That takes about one second.

A minute contains 60 seconds. When 60 minutes have passed, one hour has passed.

The Earth is always turning. One full turn is called a rotation on its axis.

For our everyday clocks, we look at the Sun. On average, it takes about 24 hours for the Sun to appear in roughly the same place in the sky again. We call this a solar day.

Dividing a day into 24 hours is an agreement people came up with a very long time ago. Nature did not draw 24 giant boxes on the Earth.

The Sun always lights roughly half of the Earth.

The side facing the Sun has daylight. The other side is darker and has night.

Because the Earth rotates, your home moves from the dark side to the light side and later back again.

It looks as if the Sun rises in the morning and sets in the evening. But you are actually standing on a huge globe that is constantly turning.

Imagine that you are eating breakfast at 08:00. At that same moment, a child somewhere else may be sleeping, having lunch or already eating dinner.

That is because the Earth is round and rotates. Not every place on Earth faces the Sun at the same time.

When it is morning in Western Europe, it may already be afternoon or evening in East Asia. Farther west, for example in parts of the Americas, the night may still be going on.

If every town used only its own position of the Sun, clocks in nearby places would already be slightly different. That would be very inconvenient for trains, planes, schools, work and appointments.

So we divided the Earth into time zones. Places in the same time zone usually use the same clock time.

The Earth rotates 360 degrees in about 24 hours.

360 ÷ 24 = 15

That is why one hour of difference in solar time roughly matches 15 degrees of longitude.

Real time zones are not neat straight strips. Countries decide which official time they use, so time-zone borders often bend around countries and regions.

Every point on Earth has a place that is almost exactly opposite it. This opposite point is called an antipode.

If you could draw an imaginary straight line from your feet through the centre of the Earth, you would come out near your antipode.

On this page you can choose your town or city. We can then show:
- roughly where the other side of the Earth is;
- what date it is there;
- what the local time is there right now.

There is often about twelve hours of difference in solar time, but the official clock time can be different because of time zones and daylight saving time.

You can travel to a place where the clock shows an earlier or later time. But that does not take you back to a moment you have already lived through.

If you fly west, for example, you often enter time zones where the clock is set back.

Imagine:
- you leave at 15:00;
- you travel for 8 hours;
- when you arrive, the local time is 17:00.

The clock makes it look as if only two hours have passed. But you really did spend eight hours on the plane.

Yes, in a way you can chase the Sun.

The Earth rotates from west to east. That makes the Sun, Moon and stars appear to move across our sky from east to west.

If you travel very fast to the west, you are travelling in the same apparent direction as the Sun across the sky. This can delay sunset for you.

At the equator, the Earth's surface moves because of rotation at about 1,670 kilometres per hour. At higher latitudes, the speed needed to keep roughly the same position of the Sun is lower.

A normal passenger plane is not fast enough everywhere and in every situation to keep the Sun in the same place forever. But westbound flights can make your day noticeably longer.

If you keep travelling west, local clocks are set back step by step. Travel east and local clocks move forward instead.

If you travelled all the way around the Earth, there has to be somewhere where we make the calendar line up again.

Otherwise, after a trip around the world, travellers would no longer have the same date as people who stayed at home.

That is why there is a special boundary on Earth: the International Date Line.

The International Date Line runs mostly through the Pacific Ocean.

Cross it in one direction and the calendar jumps forward by one day. Cross it in the other direction and the calendar goes back by one day.

That sounds like time travel, but your body does not suddenly become one day younger or older. Only the name of the date changes.

The line is not perfectly straight. It bends so that countries and island groups are not awkwardly split between two calendar dates.

Many European countries use daylight saving time for part of the year.

In spring, the clock moves forward by one hour. In autumn, it moves back by one hour.

This is a human agreement. The Earth does not suddenly rotate faster and the Sun does not change its route.

A simple reminder in English is:

Spring forward, fall back.

While the Earth rotates on its axis, it also travels around the Sun.

One trip around the Sun takes about 365.2422 days.

That is a little longer than 365 days. So usually once every four years we add an extra calendar day: 29 February.

A year with that extra day is called a leap year.

The rule is a little cleverer than simply “every four years”, because otherwise the difference would still become too large over a very long time.

Now things get strange.

According to Albert Einstein's theory of relativity, time does not pass at exactly the same rate under all circumstances.

If you move extremely fast, your time can pass a tiny bit differently from the time of someone moving more slowly. Gravity also affects how quickly time passes.

With ordinary cars, bicycles and planes, the difference is tiny for people. But scientists can measure such differences with extremely accurate atomic clocks.

Have you ever played for an hour and felt as if only ten minutes had passed? And have you ever waited for five minutes that seemed to last forever?

The clock ran normally in both cases. But your sense of time can change.

When you are having fun or completely absorbed in something, you may notice the passing time less. When you are bored or nervously waiting, the same amount of time can feel much longer.

That is why people say:

Time flies!

It does not mean time really has wings.

With every second that passes, you have experienced a little more of your life.

A clock does not make you older. It only shows how much time has passed.

You can turn a clock back. You can even fly to a time zone where the clock shows an earlier time. But you cannot restart a moment you have already lived.

That is what makes time special.

Good moments do not always have to pass as quickly as possible. Sometimes it is nice to look carefully, listen and remember what you are experiencing.

You can measure time, plan it, share it and experience it. But unfortunately, you cannot keep it in a box.

You are almost at the end of your time adventure. Test what you have discovered.

After each question, you immediately get an explanation of the answer. At the end you receive a score: