2 times 12 hour count

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24-hour count 2 times 12 hour count
00:00 12:00 a. m. / midnight *
00:01 12:01 a. m. ( ante meridiem )
01:00 01:00 a. m.
02:00 02:00 a. m.
... ...
10:00 10:00 a. m.
11:00 11:00 a. m.
11:59 11:59 a. m. ( ante meridiem )
12:00 12:00 p. m. / noon *
12:01 pm 12:01 p. m. ( post meridiem )
13:00 01:00 p. m.
14:00 02:00 p. m.
... ...
22:00 10:00 p. m.
23:00 11:00 p. m.
23:59 11:59 p. m. ( post meridiem )
24:00 ** 12:00 a. m. / midnight *
*Since 12 a. m. and 12 p. m. are ambiguous, midnight or noon is often preferred in English .
** Rare
Astronomical clock in Ulm
Small clock: outside with long pointer with hand
Large clock : inside with short pointer and sun (instead of 1 to 24 is numbered twice from 1 to 12)

The 2-by-12-hour counting is the two-time counting of the full day, divided into 24 equinoxed hours of equal length , i.e. the light day and night together, with the help of the so-called small clock .

The historical 12-hour count

Until the invention of the mechanical clock and its spread in modern times , day and night were only considered to be part of a period of time by astronomers . This happened in Greek astronomy at least since Hipparchus , it was spread over the ancient world by Hellenism and also adopted by Arab astronomy.

In public life, day and night were treated as separate periods of time and divided into hours. A subdivision into twelve temporal hours each (varying in length over the year) has been made in the Mediterranean region since around classical Greek antiquity and then spread throughout Europe. The number 12 relates on the one hand to the sexagesimal system that originated in Babylonia (calculation based on 60) and on the other hand to the 12 lunar months that make up a lunar year . It is also reflected in the 2-by-12-hour counting of the full day, which is still common today.

Appearance of a 2-by-12-hour count

Among astronomically educated people, the 24-hour counting became decisive from the late Middle Ages , when with the advent of mechanical clocks the separate counting of day and night with twelve temporal hours of different lengths each became obsolete. For practical reasons, however, this method of counting did not become established in daily life, even when mechanical clocks spread in the 15th century and the different times of day and night hours depending on the season were abandoned in many places. Instead, the full day was now divided into two equally long twelve-hour intervals and only counted up to a twelfth hour in each of them. The traditional, separate 12-hour counting for day and night times remained, although the mechanically measured hours were now always the same length and the transition from day to night counting no longer coincided with the onset of dusk.

The small clock rotates two times in 24 hours and shows two different ones of the 24 hours of the full day at every point on the dial, which is scaled into twelve segments: 1 o'clock and 1 o'clock with an "I"; 12 noon and midnight with "XII".

The reasons for this development can be named:

  • The first public mechanical clocks were striking tower clocks that did not yet show the time of day . These acoustic clocks never used more than twelve sound signals because so many tower clock strikes were not meaningful to count.
  • The small mechanical watch was easier to construct and lasted longer than the large watch .

Current usage

Almost all wheel clocks currently in use are small clocks with the hour digits 1 to 12. Sometimes the digits 13 to 24 are added to the digits 1 to 12 to simplify the 24-hour count. The latter became the counting officially used in timetables and timetables in most of the world in the 20th century.

The 2-by-12-hour counting, usually with the addition a. m. (for “mornings”) or p. m. (for "afternoons"), is still used in writing in public life in parts of the English-speaking world as well as throughout Latin America and the Philippines . However, it is still dominant in oral use in many European countries. In German, for example, the regionally different expressions for started hours (for example “three quarters four” for 3:45 p.m.) are only associated with 12-hour counting and never with 24-hour counting.

The Latin abbreviations “a. m. ”( ante meridiem = before noon) and“ p. m. ”( post meridiem = after noon) are mainly used in the American region in English, Spanish and Portuguese. In Albania “PD” and “MD” are used, in Greece “πµ” and “µµ” are used, while in Sweden (where the 2-by-12-hour counting is now becoming less important) the abbreviations “fm” ( formiddag ) and "em" ( eftermiddag ) can be used. In many languages ​​and regions, however, abbreviations for “morning” and “afternoon” are not used.

With the advent of digital clocks , the 2 x 12 hour counting has lost its importance in everyday life. Pointer watches with a 24-hour display are rare. In those regions where 24-hour counting is uncommon, digital clocks also show 12 hours twice.

Historical use in timetables

Salzkammergut local railway timetable from 1896 with minute underlining

On the German railway timetables, the minutes to the night times were underlined ( 6 18 pm ), on Tagzeiten the underline accounted ( 6 18 am ). This regulation was in effect at the German Reichsbahn until 1927.

The Prussian State Railways timetable book contained the following information:

"The time of 6 00 evening to 5 59 in the morning , the minute numbers are indicated by underlining."

See also

literature

  • Robert V. Levine : A Map of Time. How cultures deal with time (original title: A Geography of Time , translated by Christa Broermann and Karin Schuler). 16th edition, Piper-TB 2978, Munich / Zurich 2011, ISBN 978-3-492-22978-4 .

Web links

Individual evidence

  1. ↑ AM . In: American Heritage® Dictionary of the English Language . 5th edition. Houghton Mifflin Harcourt, 2011 ( ahdictionary.com ).
  2. ↑ Jörg Meyer: The sundial and its theory. Harry Deutsch, 2008, ISBN 978-3-8171-1824-3 , p. 100.
  3. ↑ Viktor von Röll : Encyclopedia of the Railway System. Second, completely revised edition. Volume 5, Berlin and Vienna 1914, p. 5.
  4. ↑ Overview of the history of the German railways 1835–1999 on railforum.de Walbrach, p. 116.