You'll notice that the launch time is written as

and not as

That's because the green time has been written using the 24 hour clock.

Let's look first at the blue time. It's written using am (short for ante meridian) to tell you that this time is before noon. The letters pm are short for post meridian which tells you that the time is after noon. This way of writing the time is called the meridian system.

The 24 hour clock is just another way of telling you whether the time is before or after noon. A time given by the 24 hour clock usually has four numbers with a colon inbetween the the 2nd and 3rd number, like this

The first two numbers tell you the hour. If these two numbers are less than 12 then you know the time is before noon. So

using the 24 clock is the same as

Noon is written as

using the 24 hour clock or,

After noon, the hours in the 24 clock system go from 13 all the way up to 24. Nobody says, however, "it's 17 o'clock, time I was away home!". A time like

is of course

You just take away the number "12" whenever you see an hour in the 24 hour clock system that is greater than 12 to get the hour in the common meridian clock.

Finally, midnight, or

A lot of timetables use the 24 hour clock, as do most European countries and scientists in general.

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