### Units of Time

There are many units used to measure time, here are some to remember:

A year is made up of **12 months**.

It is also made up of **365 days** (366 in a leap year).

And it has **52 weeks**.

A month is made up of either 30 or 31 days or in the case of February 28 days (but 29 in a leap year).

A week is made up of **7 days**.

A day is made up of **24 hours**.

An hour is made up of **60 minutes**.

A minute is made up of **60 seconds**.

To remember the number of days in each month it is worth learning this saying:

“30 days have September, April, June and November. All the rest have 31, except for February alone, which has 28 days clear, and 29 in a leap year.”

A leap year happens once **every 4 years** and the only thing that changes is that **February has an extra day**.

### Telling the time

There are 2 different ways of reading and writing time, the **12 hour clock**, and the **24 hour clock**.

## The 12 hour clock

A typical **12 hour clock** shows **12 hours** around it’s face, like this:

The **short hand** points to the **hours** and the **long hand** points to the **minutes**.

The clock above shows the time to be **half past three**. This can also be written:

3:30

When reading a 12 hour clock it is important to know that each time on the clock is shown **twice every day**. There are 24 hours in a day and just 12 hours on the face of the clock, so the hour hand will go all the way round the clock **twice** every day.

**From 12 midnight to 12 noon**, the morning time, we call

am

**From 12 noon until 12 midnight**, the afternoon and evening time, we call

pm

We don’t know from looking at the picture of the clock above if it is 3:30 in the **morning** or 3:30 in the **afternoon**! But if we were told it was **3:30 pm** we would know it was 3:30 in the afternoon.

## The 24 hour clock

The 24 hour clock shows time like this:

The 24 hour clock does **not stop at 12:00** like the 12 hour clock, it keeps going to 13:00, then 14:00 and so on all the way up to 23:59.

Then at **middnight** it starts all over again at **00:00**.

An hour after 12 midday we go to **1:00 pm** on the 12 hour clock. On the 24 hour clock this looks like this:

The next hour after 13:00 is **14:00** – this is **2 pm**.

In the hours **before 12:00** (midday) an extra ‘0’ is added to the 24-hour clock time at the start, so **8 am** looks like this:

Here is the time 3:30 pm shown on a 24 hour clock:

The **hours are on 15** and the **minutes on 30**. This tells us it is **half past three in the afternoon**.

If you get confused by the hours on a 24 hour clock you can **take away 12 from the hours**:

15:30 – 12 = 3:30

Don’t forget it will always be **pm** if you have used this method of subtracting 12.

**3:30 pm** on the 12 hour clock and **15:30** on the 24 hour clock are the same time.

### Speed

Speed is the measure of distance over time.

Speed is often measured in **miles per hour (mph)**. Or **kilometers per hour(kph)**.

You can think of speed as a measure of how far you can go in an hour.

Imagine that a space ship is flying up in to space, the faster it goes, the further it will get in an hour.