That's a very good question!

From morning until night,

clocks help us to plan our day.

They tell us when things begin and when they end.

Before clocks, people told time by watching the sun move across the sky.

They started work when the sun came up in the east.

At noon, when the sun was very high,

they ate and rested.

When the sun disappeared in the west, they went to bed.

Today, we know that the sun doesn't move around the Earth.

The Earth turns, or spins, on an imaginary line called an axis.

As the Earth turns, the sun seems to be moving across the sky.

The time it takes for the Earth to make one complete turn

is called a day.

A day is divided into hours, minutes, and seconds.

There are 24 hours in a day.

There are 60 minutes in an hour.

How many minutes are there in a day?

Multiply 24 hours times 60 minutes to get the answer.

24 X 60=1,440.

There are 1,440 minutes in one day!

We measure time by other movements, too.

The Earth travels around, or orbits, the sun.

The time it takes for the Earth to go around the sun once is called a year.

One year is equal to 12 months,

or just over 52 weeks.

To be very accurate,

it takes the Earth 365 days, 5 hours,

49 minutes, and 12 seconds to go around the sun.

We divide the Earth into 24 time zones.

Each time zone is one hour apart from the next time zone.

For example, when it is10:00 a.m. where you live,

it is 10:00 p.m. on the opposite side of the world.

In two hours, it will be noon where you live,

but on the other side of the world, it will be 12:00 at night!

Thanks to clocks and calendars,

we can measure time very easily.

However, it is the movement of the Earth

that really allows us to measure time.