24-hour clock

24-hour clock  12-hour clock  Period 00:00  12:00 AMmidnight  PostmidnightOvernight 01:00  1:00 AM 02:00  2:00 AM 03:00  3:00 AM 04:00  4:00 AM 05:00  5:00 AM 06:00  6:00 AM  Morning 07:00  7:00 AM 08:00  8:00 AM 09:00  9:00 AM 10:00  10:00 AM 11:00  11:00 AM 12:00  12:00 PMnoonmidday  Afternoon 13:00  1:00 PM 14:00  2:00 PM 15:00  3:00 PM 16:00  4:00 PM 17:00  5:00 PM 18:00  6:00 PM  Evening 19:00  7:00 PM 20:00  8:00 PM 21:00  9:00 PM 22:00  10:00 PM 23:00  11:00 PM

The 24-hour clock is a method of telling the time in which the civil day runs from midnight until next midnight.

The following numbers (used once in the same civil day) of hours are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 and 23, without AM nor PM.

This system is also referred to (only in the United States and the English speaking parts of Canada) as military time or  (only in the United Kingdom and now very rarely) as continental time. 

In some parts of the world, it is called railway time. Also, the international standard notation of time (ISO 8601) is based on this format.
Particulars
A time in the 24-hour clock is written in the form hours:minutes (for example, 01:23), or hours:minutes:seconds (01:23:45). Numbers under 10 have a zero in front (called a leading zero); e.g. 09:07. Under the 24-hour clock system, the day begins at midnight, 00:00. The last minute of the day begins at 23:59 and ends at 24:00, which is the same as 00:00 of the following day. This means that "Tuesday at 24:00" and "Wednesday at 00:00" are the same time. Because of this, 12:00 is always noon.

Advantages over the 12-hour clock system:
 Less confusion between morning and evening.
 12:00 is always midday.

Application
Regional
In many African, Asian, European and Latin American countries people use it to write the time. Many people use it in speaking. Many digital wristwatches and clocks can display the time of day using the 24-hour clock.
Military
The U.S. military prefers not to say 24:00 - they do not like to have two names for the same thing, so they always say "23:59", which is one minute before midnight.thumb|right|A 24-hour clock face
24-hour clock time is used in computers, by the militaries, for public safety, and in transport.

Railway
In railway timetables 24:00 means the end of the day. For example, a train due to arrive at a station during the last minute of a day arrives at 24:00; but trains which depart during the first minute of the day go at 24:00. To write shop opening hours until midnight use, for example, "24:00–24:00", "07:00–24:00". v  67

Related pages
Time
Clock
Space
Physics
Spacetime
Kinematics
Radioactivity
Albert Einstein
Atomic physics
General Relativity
Erwin Schrödinger
Classical mechanics
Quantum mechanics
Unit of Measurement
International System of Units (SI units)

References

Category:Time
Category:Clocks