We explain what the acronyms am and pm mean and their equivalence to the 24-hour system. Also, how do you indicate 12 noon?
What do the acronyms am and pm mean?
In the twelve-hour time system, the dominant system in the world, The day is divided into two equal segments of 12 hours each, called ante meridiem (from Latin “before noon”), abbreviated am; and post meridiem (from Latin “after noon”), abbreviated pm
In this way, the hours of each period are numbered from 0 to 12, and to distinguish them from each other, these two abbreviations are used. Thus, 8 am is equivalent to 8 in the morning, while 8 pm is equivalent to eight in the afternoon. The only exception to the rule is noon, since at 12 noon the acronym always accompanies m. (from Latin meridiansthat is, “noon”).
These acronyms are always written accompanied by a period and separated by a space. and are often marked on automatic clocks and alarm clocks. They are not used, however, in the 24-hour time system, also known as the military time system, since in this the hours are counted from 00:00 to 24:00, without room for ambiguity. In some countries one system is preferred over the other, although the use of the 12-hour system is much more common.
The following is a table of equivalences between both systems:
| 24 hour system | 12 hour system |
| 00:00 | 12:00 am |
| 01:00 | 1:00 a.m. |
| 02:00 | 2:00 a.m. |
| 03:00 | 3:00 a.m. |
| 04:59 | 4:59 a.m. |
| 06:30 | 6:30 a.m. |
| 12:00 | 12:00 p.m. |
| 13:30 | 1:00 p.m. |
| 14:50 | 2:50 p.m. |
| 17:00 | 5:00 p.m. |
| 22:22 | 10:22 p.m. |
| 23:00 | 11:00 p.m. |
| 23:59 | 11:59 p.m. |
This 12-hour system was the traditional time system inherited from ancient times. classical, and was the only one that existed until the 19th century, when the Canadian inventor and engineer, of Scottish origin, Sandford Fleming (1827-1915) proposed the 24-hour timetable, as part of the creation of universal standard time, that is, of the time zone system to determine the time anywhere in the world, using the Greenwich Meridian as the date change point.
Why is only m used? to indicate 12 noon?
If the logic of the 12-hour time system is to divide the day into two equal blocks, one before noon (am) and the other after (pm), it is normal that the doubt arises as to which of the two blocks noon corresponds to, that is, 12 noon. And the answer is that none, since In this case, the acronym is used m. to indicate that it is precisely noon . Instead, For twelve at night, 12 am is used. since this time takes place at the beginning of the day, twelve hours before the day is halfway through.
References
- “12-hour time system” on Wikipedia.
- “If the abbreviation “am” is used to indicate the hours before noon and “pm” for those after noon, which one is used to indicate 12 noon?” in Spanish up to date from the Royal Spanish Academy.
- “Where do the acronyms AM and PM come from?” in Heraldo (Spain).
