Everything about A M totally explained
| clock system |
| 12-hour |
a href=http://24-hour_clock.totallyexplained.com title="24-hour clock - Totally Explained">24-hour |
midnight
12:00 a.m.* |
00:00 |
| 1:00 a.m. |
01:00 |
| 2:00 a.m. |
02:00 |
| 3:00 a.m. |
03:00 |
| 4:00 a.m. |
04:00 |
| 5:00 a.m. |
05:00 |
| 6:00 a.m. |
06:00 |
| 7:00 a.m. |
07:00 |
| 8:00 a.m. |
08:00 |
| 9:00 a.m. |
09:00 |
| 10:00 a.m. |
10:00 |
| 11:00 a.m. |
11:00 |
noon
12:00 p.m.* |
12:00 |
| 1:00 p.m. |
13:00 |
| 2:00 p.m. |
14:00 |
| 3:00 p.m. |
15:00 |
| 4:00 p.m. |
16:00 |
| 5:00 p.m. |
17:00 |
| 6:00 p.m. |
18:00 |
| 7:00 p.m. |
19:00 |
| 8:00 p.m. |
20:00 |
| 9:00 p.m. |
21:00 |
| 10:00 p.m. |
22:00 |
| 11:00 p.m. |
23:00 |
undefined
(midnight)* |
24:00 |
* See section "Confusion
at noon and midnight" |
The
12-hour clock is a
timekeeping convention in which the 24
hours of the
day are divided into two periods called
ante meridiem (
a.m.,
Latin "before noon") and
post meridiem (
p.m., "after noon"). Each period consists of 12 hours numbered 12 (acting as zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The indication of noon and midnight in the 12-hour system is disputed.
The 12-hour clock was developed over time from the mid-second millennium BC, to the 16th century A.D. and was once popular throughout Northern Europe, but is now used as the dominant system in only a few former
British and
American Colonies. It is also used informally in most of the world. The notion has received much criticism, yet survives out of tradition.
History and use
The 12-hour clock can be traced back as far as
Mesopotamia and
Ancient Egypt, but may also have roots in
Ancient India. The lengths of the ancient hours varied seasonally, always with 12 hours from
sunrise to
sunset and 12 hours from sunset to sunrise. In Egypt the hour beginning and ending each half-day (four hours each day) were considered twilight hours. An Egyptian
sundial for daylight use and an Egyptian
water clock for nighttime use found in the tomb of Pharaoh
Amenhotep I, both dating to c. 1500 BC, divided these periods into 12 hours each.
The
Romans also used a 12-hour clock: the day was divided into 12 equal hours (of, thus, varying length throughout the year) and the night was divided into three watches. The Romans numbered the morning hours originally in reverse. For example, "3 a.m." or "3 hours ante meridiem" meant "three hours before noon", compared to the modern meaning of "three hours after midnight".
The first mechanical clocks in the
14th century, if they'd dials at all, showed all 24 hours, using the
24 hour analog dial, influenced by astronomers' familiarity with the
astrolabe and
sundial, and their desire to model the
apparent motion of the
sun. In
Northern Europe these dials generally used the 12 hour
numbering scheme in
Roman numerals, but showed both a.m. and p.m. periods in sequence. This is known as the Double-XII system, and can be seen on many surviving clock faces, such as those at
Wells and
Exeter. Elsewhere in Europe, particularly in Italy, numbering was more likely to be based on the 24 hour system (I to XXIV), reflecting the Italian style of counting the
hours.
During the 15th and 16th centuries the 12 hour analog dial and time system, with its simpler and more economical construction, gradually became established as standard throughout Northern Europe for general public use. The 24 hour analog dial was reserved for the more specialist applications, such as for
astronomical clocks and chronometers.
Most
analog clocks and watches today use the 12-hour dial, on which the
hour hand (shorter and sometimes thicker) rotates once every 12 hours and twice in a day. They are used even in cultures where the
24-hour notation is otherwise preferred. Some 12-hour dials show the numbers 13 to 23 written inside the primary 1 to 12 ring.
Use by country
» Main article: Date and time notation by country
Although it has largely been replaced today by the
24-hour notation around the world, especially in written communication, the 12-hour notation with a.m. and p.m. suffixes is common in some parts of the world.
It is commonly used alongside the 24-hour clock in: » * Albania
* Brazil » * Greece
* Quebec, Canada » * Ireland
* Singapore » * United Kingdom and other English-speaking regions
* some Spanish-speaking regions of South America
In many European countries, a 12-hour clock is commonly used in informal speech, but a.m. and p.m. are little known. If one wants to unambiguously refer to time in the 12-hour system, one uses descriptive phrases instead, such as in the morning, in the afternoon, in the evening, at night.
Abbreviations
The Latin abbreviations "a.m." and "p.m." (often written "am" and "pm"; "AM" and "PM"; and "A.M." and "P.M.") are used in English and Spanish. The equivalents in Greek are "πµ" and "µµ".
Most other languages lack formal abbreviations for "before noon" and "after noon" and their users use the 12-hour clock only orally and informally.
Criticism and practical problems
24-hour clock may see the 12-hour notation as a less practical and outdated convention, especially in the context of written communication, computers and digital clocks. The arguments for or against a change may be compared to the discussion on metrication. Even people who grew up with the 12-hour clock, however, often have problems indicating midnight and noon. Those who grew up with the 24-hour clock are also confused when they come across situations very common in, for example, Internet forums and email in which a message indicated as posted at "12:46 am" appears unintuitively and seemingly illogically before a message marked "11:05 am" for example.
The disadvantages most commonly voiced by critics in comparing the 12-hour notation to the 24-hour clock are:
confusion about the correct notation for noon and midnight
confusion about the difference between midnight at the start and end of a given date
The rollover from 12 to 1 happens an hour later than the change between a.m. and p.m.
The lexicographical order doesn't match the chronological order.
It's generally more complicated to understand and to implement in software and digital electronics.
Typographically, the a.m. and p.m. terms require more space.
Confusion at noon and midnight
Further Information
Get more info on 'A M'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://12-hour_clock.totallyexplained.com">12-hour clock Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
