What time is 17 a clock?

Have you ever wondered how to read military time quickly and easily? Or even wondered what it was, or why it exists? Well, welcome to the Internet’s greatest authority resource on just that! On this page, you will find the answers to that and more in great detail, in other words, everything you will ever need to know about military time (or astronomical time), as well as some quick and easy tips on how to read it.

It is based on a 24 hour clock, and is a method of keeping hours in which the day runs from midnight to midnight and is divided into 24 hour increments. It is the most commonly used interval notation in the world.

Easy to Read Military Time Chart

A side-by-side look at the 12 hour clock times and the corresponding military/24 hour clock times, provided exclusively by Military Time Chart. You may use this as a military time converter, or reference it as a military time conversion chart.
  12-hour am-pm clock24-hour military time

12:00 midnight	00:00
1:00 am	01:00
2:00 am	02:00
3:00 am	03:00
4:00 am	04:00
5:00 am	05:00
6:00 am	06:00
7:00 am	07:00
8:00 am	08:00
9:00 am	09:00
10:00 am	10:00
11:00 am	11:00
12:00 pm	12:00
1:00 pm	13:00
2:00 pm	14:00
3:00 pm	15:00
4:00 pm	16:00
5:00 pm	17:00
6:00 pm	18:00
7:00 pm	19:00
8:00 pm	20:00
9:00 pm	21:00
10:00 pm	22:00
11:00 pm	23:00
12:00 midnight	24:00

How to Read Military Time

When keeping hours in this fashion, the day starts at midnight and is written as 00:00. The last minute of the day is written as 23:59, or one minute before the next midnight. Sometimes you may see 00:00 written as 24:00. Both are acceptable. A usage example showing  the 12 hour clock vs military time would be a time table showing 4:00 pm to 12:00 midnight. This would be written as 16:00 – 24:00. Another example highlighting the difference between the two would be to show that 10:15 am is written as 10:15 in military time but 2:30 pm is written as 14:30.

This method of keeping time is most commonly used by the military, government, public transportation, hospitals, meteorologists, astronomers, those employed in emergency services, and also with computers. When speaking in military time, 07:00 may be stated as “zero seven hundred” or “oh seven hundred”. Also, in the military, these time stamps are often written without the colon, so 07:52 would rather be written 0752.

Time stamps referencing Greenwich Mean Time (GMT for short – often interchanged with Coordinated Universal Time/UTC) is denoted by a “Z” at the end, and is written as 0752Z. The local time is denoted by a “J” at the end, and the eastern time zone is denoted by an “R” at the end. Each of the zones have a corresponding letter and name.

Military Time Converter

For other methods of keeping time, see our article on the lunar calendar, the Mayan Calendar, the Chinese Calendar, the Gregorian Calendar, and All About Sundials.

Other top posts:

• Military Pay Chart
• Military Star Card
• Military Alphabet

References: Wikipedia: 24 hour clock

Timekeeping convention

The modern 24-hour clock, popularly referred to in the United States as military time,[1][2] is the convention of timekeeping in which the day runs from midnight to midnight and is divided into 24 hours. This is indicated by the hours (and minutes) passed since midnight, from 0(:00) to 23(:59). This system, as opposed to the 12-hour clock, is the most commonly used time notation in the world today,[1] and is used by the international standard ISO 8601.[3]

A number of countries, particularly English-speaking, use the 12-hour clock, or a mixture of the 24- and 12-hour time systems. In countries where the 12-hour clock is dominant, some professions prefer to use the 24-hour clock. For example, in the practice of medicine, the 24-hour clock is generally used in documentation of care as it prevents any ambiguity as to when events occurred in a patient's medical history.[4]

24-hour clock 12-hour clock

00:00	12:00 (midnight)[a] 12:00 a.m. (start of the day)
01:00	1:00 a.m.
02:00	2:00 a.m.
...	...
10:00	10:00 a.m.
11:00	11:00 a.m.
12:00	12:00 noon[a] 12:00 p.m.
13:00	1:00 p.m.
14:00	2:00 p.m.
...	...
22:00	10:00 p.m.
23:00	11:00 p.m.
24:00 equals 00:00 next day	12:00 (midnight)[a] (end of the day)
^ a b c See: Confusion at noon and midnight

Description

World map showing the usage of 12 or 24-hour clock in different countries

  24 hours

  24 hours (12 orally)

  Both in common use

  12 hours

24-hour digital clock in Miaoli HSR station.

A time of day is written in the 24-hour notation in the form hh:mm (for example 01:23) or hh:mm:ss (for example, 01:23:45), where hh (00 to 23) is the number of full hours that have passed since midnight, mm (00 to 59) is the number of full minutes that have passed since the last full hour, and ss (00 to 59) is the number of seconds since the last full minute. In the case of a leap second, the value of ss may extend to 60. A leading zero is added for numbers under 10, but it is optional for the hours. The leading zero is very commonly used in computer applications, and always used when a specification requires it (for example, ISO 8601).

Where subsecond resolution is required, the seconds can be a decimal fraction; that is, the fractional part follows a decimal dot or comma, as in 01:23:45.678. The most commonly used separator symbol between hours, minutes and seconds is the colon, which is also the symbol used in ISO 8601. In the past, some European countries used the dot on the line as a separator, but most national standards on time notation have since then been changed to the international standard colon. In some contexts (including some computer protocols), no separator is used and times are written as, for example, "2359".

Midnight 00:00 and 24:00

"23:59" redirects here. For the Christian metal album, see Veni Domine. For the film, see 23:59 (film).

In the 24-hour time notation, the day begins at midnight, 00:00 or 0:00, and the last minute of the day begins at 23:59. Where convenient, the notation 24:00 may also be used to refer to midnight at the end of a given date[5] — that is, 24:00 of one day is the same time as 00:00 of the following day.

The notation 24:00 mainly serves to refer to the exact end of a day in a time interval. A typical usage is giving opening hours ending at midnight (e.g. "00:00–24:00", "07:00–24:00"). Similarly, some bus and train timetables show 00:00 as departure time and 24:00 as arrival time. Legal contracts often run from the start date at 00:00 until the end date at 24:00.

While the 24-hour notation unambiguously distinguishes between midnight at the start (00:00) and end (24:00) of any given date, there is no commonly accepted distinction among users of the 12-hour notation. Style guides and military communication regulations in some English-speaking countries discourage the use of 24:00 even in the 24-hour notation, and recommend reporting times near midnight as 23:59 or 00:01 instead.[6] Sometimes the use of 00:00 is also avoided.[6] In variance with this, as of 2010, the correspondence manual for the United States Navy and United States Marine Corps formerly specified 0001 to 2400.[7] The manual was updated in June 2015 to use 0000 to 2359.[8]

Times after 24:00

See also: Date and time notation in Japan § Time

Time-of-day notations beyond 24:00 (such as 24:01 or 25:00 instead of 00:01 or 01:00) are not commonly used and not covered by the relevant standards. However, they have been used occasionally in some special contexts in the United Kingdom, France, Spain, Canada, Japan, South Korea, Hong Kong, and China where business hours extend beyond midnight, such as broadcast television production and scheduling. The GTFS public transport schedule listings file format has the concept of service days and expects times beyond 24:00 for trips that run after midnight.[9]

Computer support

In most countries, computers by default show the time in 24-hour notation. For example, Microsoft Windows and macOS activate the 12-hour notation by default only if a computer is in a handful of specific language and region settings. The 24-hour system is commonly used in text-based interfaces. POSIX programs such as ls default to displaying timestamps in 24-hour format.

Military time

24-hour clock as seen on the USS Midway.

In American English, the term military time is a synonym for the 24-hour clock.[10] In the US, the time of day is customarily given almost exclusively using the 12-hour clock notation, which counts the hours of the day as 12, 1, ..., 11 with suffixes a.m. and p.m. distinguishing the two diurnal repetitions of this sequence. The 24-hour clock is commonly used there only in some specialist areas (military, aviation, navigation, tourism, meteorology, astronomy, computing, logistics, emergency services, hospitals), where the ambiguities of the 12-hour notation are deemed too inconvenient, cumbersome, or dangerous.

Military usage, as agreed between the United States and allied English-speaking military forces,[11] differs in some respects from other twenty-four-hour time systems:

• No hours/minutes separator is used when writing the time, and a letter designating the time zone is appended (for example "0340Z").
• Leading zeros are always written out and are required to be spoken, so 5:43 a.m. is spoken "zero five forty-three" (casually) or "zero five four three" (military radio), as opposed to "five forty-three" or "five four three".
• Military time zones are lettered and given word designations from the NATO phonetic alphabet. For example, in US Eastern Standard Time (UTC−5), which is designated time zone R, 2:00 a.m. is written "0200R" and spoken "zero two hundred Romeo".
• Local time is designated as zone J or "Juliett". "1200J" ("twelve hundred Juliett") is noon local time.
• Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC) is designated time zone Z, and thus called "Zulu time". (When used as a modern time zone, in practice, GMT and UTC coincide. For other purposes there may be a difference of about a second.[12])
• Hours are always "hundred", never "thousand"; 1000 is "ten hundred" not "one thousand"; 2000 is "twenty hundred" not "two thousand".

History

Paolo Uccello's Face with Four Prophets/Evangelists (1443) in the Florence Cathedral

The 24-hour tower clock in Venice that lists hours 1 to 12 twice

The first mechanical public clocks introduced in Italy were mechanical 24-hour clocks which counted the 24 hours of the day from one-half hour after sundown to the evening of the following day. The 24th hour was the last hour of day time.[13]

From the 14th to the 17th century, two systems of time measurement competed in Europe:[14][15]

• Italian (Bohemian, Old-Bohemian) hours (full-dial): 24 hours system with the day starting after sunset; on the static dial, the 24th hour was situated on the right side. In Italy, it was prevalently modified to a 4×6 hours system, but some 24hour dials lasted until the 19th century. The system has spread especially to the Alpine countries, Czech countries and Poland. In Bohemia, this system was finally banned only 1621 after the defeat on White Mountain. The Prague Astronomical Clock struck according to the Old Bohemian Clock until its destruction in 1945. The variant with counting from dawn is also rarely documented and used, e.g. on a 16th-century cabinet clock in the Vienna Art-History Museum.[16]
• German (Gallic) hours (half-dial): 2×12 hour system starting ad midnight and restarted at noon. It is typical with the 12hours dial with 12 at the top.

The modern 24hour system is a late-19th century adaptation of the German midnight-starting system, and then prevailed in the world with the exception of some Anglophone countries.

Striking clocks had to produce 300 strokes each day, which required a lot of rope, and wore out the mechanism quickly, so some localities switched to ringing sequences of 1 to 12 twice (156 strokes), or even 1 to 6 repeated four times (84 strokes).[13]

After missing a train while travelling in Ireland in 1876 because a printed schedule listed p.m. instead of a.m., Sir Sandford Fleming proposed a single 24-hour clock for the entire world, located at the centre of the Earth, not linked to any surface meridian — a predecessor to Coordinated Universal Time.[17][18] He was an early proponent of using the 24-hour clock as part of a programme to reform timekeeping, which also included establishing time zones and a standard prime meridian.[19] The Canadian Pacific Railway was among the first organizations to adopt the 24-hour clock, at midsummer 1886.[17][20]

At the International Meridian Conference in 1884, American lawyer and astronomer Lewis M. Rutherfurd proposed:

That this universal day is to be a mean solar day; is to begin for all the world at the moment of midnight of the initial meridian coinciding with the beginning of the civil day and date of that meridian, and is to be counted from zero up to twenty-four hours.[21]

This resolution was adopted by the conference.[21]

The Shepherd Gate Clock with Roman numerals up to XXIII (23) and 0 for midnight, in Greenwich

A report by a government committee in the United Kingdom noted Italy as the first country among those mentioned to adopt 24-hour time nationally, in 1893.[22] Other European countries followed: France adopted it in 1912 (the French army in 1909), followed by Denmark (1916), and Greece (1917). By 1920, Spain, Portugal, Belgium, and Switzerland had switched, followed by Turkey (1925), and Germany (1927). By the early 1920s, many countries in Latin America had also adopted the 24-hour clock.[23] Some of the railways in India had switched before the outbreak of the war.[22]

During World War I, the British Royal Navy adopted the 24-hour clock in 1915, and the Allied armed forces followed soon after,[22] with the British Army switching officially in 1918.[24] The Canadian armed forces first started to use the 24-hour clock in late 1917.[25] In 1920, the United States Navy was the first United States organization to adopt the system; the United States Army, however, did not officially adopt the 24-hour clock until World War II, on July 1, 1942.[26]

A Russian 24-hour watch for polar expeditions from 1969, made by Soviet watchmaker Raketa.

The use of the 24-hour clock in the United Kingdom has grown steadily since the beginning of the 20th century, although attempts to make the system official failed more than once.[27] In 1934, the British Broadcasting Corporation (BBC) switched to the 24-hour clock for broadcast announcements and programme listings. The experiment was halted after five months following a lack of enthusiasm from the public, and the BBC continued using the 12-hour clock.[27] In the same year, Pan American World Airways Corporation and Western Airlines in the United States both adopted the 24-hour clock.[28] In modern times, the BBC uses a mixture of both the 12-hour and the 24-hour clock.[27] British Rail and London Transport switched to the 24-hour clock for timetables in 1964.[27] A mixture of the 12- and 24-hour clocks similarly prevails in other English-speaking Commonwealth countries: French speakers have adopted the 24-hour clock in Canada much more broadly than English speakers, and Australia also uses both systems.

See also

• 12-hour clock
• 24-hour analog dial
• Clock
• Date and time representation by country
• Decimal time
• Hindu units of time
• Italian six-hour clock
• List of military time zones
• Metric time
• Thai six-hour clock
• Time
• Traditional Chinese timekeeping

Notes

References

1. ^ a b See the Common Locale Data Repository for detailed data about the preferred date and time notations used across the world, as well the locale settings of major computer operating systems, and the article Date and time representation by country.
2. ^ U.S. Government Printing Office, Style Manual. "12. Numerals". Archived from the original on 2008-04-21. Retrieved 2007-09-02.
3. ^ International Standard ISO 8601: Data elements and interchange formats – Information interchange – Representation of dates and times. International Organization for Standardization, 3rd ed., 2004.
4. ^ Pickar, Gloria D.; Graham, Hope; Swart, Beth; Swedish, Margaret (2011). Dosage calculations (2nd Canadian ed.). Toronto: Nelson Education. p. 60. ISBN 9780176502591.
5. ^ ISO 8601:2004 Data elements and interchange formats – Information interchange – Representation of dates and times, clause 4.2.3 Midnight
6. ^ a b "Communication instructions – General Archived 2011-08-07 at the Wayback Machine", Allied Communications Publication ACP 121(I), page 3–6, Combined Communications-Electronics Board, October 2010
7. ^ SECNAV M-5216.5 Department of the Navy Correspondence Manual dated March 2010, Chapter 2, Section 5 Paragraph 15. Expressing Military Time.
8. ^ "Manual" (PDF). /www.marines.mil. June 2015.
9. ^ "Reference | Static Transit". Google Developers.
10. ^ "military time". Lexico UK English Dictionary. Oxford University Press. Archived from the original on November 12, 2020.
11. ^ "Communication Instructions General ACP 121(I)" (PDF). Archived from the original (PDF) on 2016-05-08.
12. ^ Guinot, Bernard (August 2011). "Solar time, legal time, time in use". Metrologia. 48 (4): 185. Bibcode:2011Metro..48S.181G. doi:10.1088/0026-1394/48/4/S08. S2CID 121852011.
13. ^ a b Dohrn-Van Rossum, Gerhard (1996). History of the Hour. Clock and Modern Temporal Orders. The University of Chicago Press. p. 114. ISBN 0226155110.
14. ^ Tomáš Voříšek: Hodiny německé a české na půl orloje a podle celého orloje, Otta z Losu, last update 2021
15. ^ Stan. Marušák, Petr Král: Čtyřiadvacetník, Orloj.eu
16. ^ Český čas s otazníkem, Orloj.eu
17. ^ a b Fleming, Sandford (1886). "Time-reckoning for the twentieth century". Annual Report of the Board of Regents of the Smithsonian Institution (1): 345–366. Reprinted in 1889: Time-reckoning for the twentieth century at the Internet Archive.
18. ^ Blaise, Clark (2001). Time lord: Sir Sandford Fleming and the creation of standard time. New York: Pantheon Books. pp. 81–82. ISBN 978-0-375-40176-3.
19. ^ Creet, Mario (1990). "Sandford Fleming and Universal Time". Scientia Canadensis: Canadian Journal of the History of Science, Technology and Medicine. 14 (1–2): 66–89. doi:10.7202/800302ar.
20. ^ The London Times reports on a timetable using the 24-hour clock on a trip from Port Arthur, Ontario: "A Canadian Tour". The Times. No. 31880. London. 2 October 1886. col 1–2, p. 8.
21. ^ a b "International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October 1884. Protocols of the proceedings". Project Gutenberg. 1884. Retrieved 30 November 2012.
22. ^ a b c "Memorandum CAB 24/110/21 (CP 1721), 'Report of the Committee upon the 24 hour method of expressing time'". The National Archives, Kew, United Kingdom. 4 August 1920.
23. ^ "History of the 24-Hour Clock - Military Time Chart - 24 Hour Time Clock". militarytimechart.net. December 24, 2016.
24. ^ The Times: 1918 September 19, p. 3.
25. ^ Dancocks, Daniel G. Gallant Canadians: The Story of the 10th Canadian Infantry Battalion 1914–1919
26. ^ The Pittsburgh Press, 1942 July 19.
27. ^ a b c d Boardman, Peter (July 2011). Counting Time: a brief history of the 24-hour clock.[self-published source]
28. ^ Sarasota Herald-Tribune 1943 May 14

External links

Wikimedia Commons has media related to 24-hour clocks.

• Counting Time: a brief history of the 24-hour clock (free e-book)

Retrieved from "//en.wikipedia.org/w/index.php?title=24-hour_clock&oldid=1122707941"

Page 2

Time counting system

"AM and PM" redirects here. For other uses, see AM PM.

The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: a.m. (from Latin ante meridiem, translating to "before midday") and p.m. (from Latin post meridiem, translating to "after midday").[1][2] Each period consists of 12 hours numbered: 12 (acting as 0),[3] 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11.

The daily cycle starts at 12 midnight, runs through 12 noon, and continues until just before midnight at the end of the day. There is no widely accepted convention for how midday and midnight should be represented. The 12-hour clock was developed from the second millennium BC and reached its modern form in the 16th century AD.

The 12-hour time convention is common in several English-speaking nations and former British colonies, as well as a few other countries.

Clock system 12-hour 24-hour

Midnight (start of day) 12 midnight 12:00 a.m.[a]	00:00
12:01 a.m.	00:01
1:00 a.m.	01:00
11:00 a.m.	11:00
11:59 a.m.	11:59
Noon 12 noon 12:00 p.m.[a]	12:00
12:01 p.m.	12:01
1:00 p.m.	13:00
11:00 p.m.	23:00
11:59 p.m.	23:59
Midnight (end of day) or shown as start of next day[a]	24:00
^ a b c See: §Confusion at noon and midnight

History and use

Exeter Cathedral Astronomical Clock, showing the double-XII numbering scheme

The natural day-and-night division of a calendar day forms the fundamental basis as to why each day is split into two cycles. Originally there were two cycles: one cycle which could be tracked by the position of the Sun (day), followed by one cycle which could be tracked by the Moon and stars (night). This eventually evolved into the two 12-hour periods which are used today, one called "a.m." starting at midnight and another called "p.m." starting at noon. Noon itself is rarely abbreviated today; but if it is, it is denoted "m."[1]

The 12-hour clock can be traced back as far as Mesopotamia and ancient Egypt.[4] Both an Egyptian sundial for daytime use[5] and an Egyptian water clock for night-time use were found in the tomb of Pharaoh Amenhotep I.[6] Dating to c. 1500 BC, these clocks divided their respective times of use into 12 hours each.

The Romans also used a 12-hour clock: daylight was divided into 12 equal hours (thus hours having varying length throughout the year) and the night was divided into four watches.

The first mechanical clocks in the 14th century, if they had dials at all, showed all 24 hours using the 24-hour analog dial, influenced by astronomers' familiarity with the astrolabe and sundial and by their desire to model the Earth's apparent motion around 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, numbering was more likely to be based on the 24-hour system (I to XXIV). The 12-hour clock was used throughout the British empire.

During the 15th and 16th centuries, the 12-hour analog dial and time system gradually became established as standard throughout Northern Europe for general public use. The 24-hour analog dial was reserved for more specialized applications, such as astronomical clocks and chronometers.

Most analog clocks and watches today use the 12-hour dial, on which the shorter hour hand rotates once every 12 hours and twice in one day. Some analog clock dials have an inner ring of numbers along with the standard 1-to-12 numbered ring. The number 12 is paired either with a 00 or a 24, while the numbers 1 through 11 are paired with the numbers 13 through 23, respectively. This modification allows the clock to also be read in 24-hour notation. This kind of 12-hour clock can be found in countries where the 24-hour clock is preferred.

Use by country

Main article: Date and time representation by country

Typical analogue 12-hour clock

World map showing the usage of 12 or 24-hour clock in different countries

  24 hours

  24 hours (12 orally)

  Both in common use

  12 hours

In several countries the 12-hour clock is the dominant written and spoken system of time, predominantly in nations that were part of the former British Empire, for example, the United Kingdom, Republic of Ireland, the United States, Canada (excluding Quebec), Australia, New Zealand, South Africa, India, Pakistan, and Bangladesh, and others follow this convention as well, such as Mexico and the former American colony of the Philippines. In most countries, however, the 24-hour clock is the standard system used, especially in writing. Some nations in Europe and Latin America use a combination of the two, preferring the 12-hour system in colloquial speech but using the 24-hour system in written form and in formal contexts.

The 12-hour clock in speech often uses phrases such as ... in the morning, ... in the afternoon, ... in the evening, and ...at night. Rider's British Merlin almanac for 1795 and a similar almanac for 1773 published in London used them.[7] Other than in English-speaking countries and some Spanish-speaking countries, the terms a.m. and p.m. are seldom used and often unknown.

Computer support

In most countries, computers by default show the time in 24-hour notation. Most operating systems, including Microsoft Windows and Unix-like systems such as Linux and macOS, activate the 12-hour notation by default for a limited number of language and region settings. This behaviour can be changed by the user, such as with the Windows operating system's "Region and Language" settings.[8]

Abbreviations

Typical digital 12-hour alarm clock indicating p.m. with a dot to the left of the hour

The Latin abbreviations a.m. and p.m. (often written "am" and "pm", "AM" and "PM", or "A.M." and "P.M.") are used in English and Spanish.[9] The equivalents in Greek are π.μ. and μ.μ., respectively, and in Sinhala පෙ.ව. (pe.va.) for පෙරවරු (peravaru, පෙර pera – fore, pre) and ප.ව. (pa.va.) for පස්වරු (pasvaru, පස්සේ passē – after, post). However, noon is rarely abbreviated in any of these languages, noon normally being written in full. In Portuguese, there are two official options and many others used, for example, using 21:45, 21h45 or 21h45min (official ones) or 21:45 or 9:45 p.m. In Irish, a.m. and i.n. are used, standing for ar maidin ("in the morning") and iarnóin ("afternoon") respectively.

Most other languages lack formal abbreviations for "before noon" and "after noon", and their users use the 12-hour clock only orally and informally.[citation needed] However, in many languages, such as Russian and Hebrew, informal designations are used, such as "9 in the morning" or "3 in the night".

When abbreviations and phrases are omitted, one may rely on sentence context and societal norms to reduce ambiguity. For example, if one commutes to work at "9:00", 9:00 a.m. may be implied, but if a social dance is scheduled to begin at "9:00", it may begin at 9:00 p.m.

Related conventions

Typography

The terms "a.m." and "p.m." are abbreviations of the Latin ante meridiem (before midday) and post meridiem (after midday). Depending on the style guide referenced, the abbreviations "a.m." and "p.m." are variously written in small capitals ("am" and "pm"),[citation needed] uppercase letters without a period ("AM" and "PM"), uppercase letters with periods, or lowercase letters ("am" and "pm" or,[10] "a.m." and "p.m.").[citation needed] With the advent of computer generated and printed schedules, especially airlines, advertising, and television promotions, the "M" character is often omitted as providing no additional information as in "9:30A" or "10:00P".[11]

Some style guides suggest the use of a space between the number and the a.m. or p.m. abbreviation.[citation needed] Style guides recommend not using a.m. and p.m. without a time preceding it.[12]

The hour/minute separator varies between countries: some use a colon, others use a period (full stop),[10] and still others use the letter h.[citation needed] (In some usages, particularly "military time", of the 24-hour clock, there is no separator between hours and minutes.[13] This style is not generally seen when the 12-hour clock is used.)

Encoding

Unicode specifies codepoints for "a.m." and "p.m." symbols, which are intended to be used only with Chinese-Japanese-Korean (CJK) character sets, as they take up exactly the same space as one CJK character:

• U+33C2 ㏂ SQUARE AM
• U+33D8 ㏘ SQUARE PM

Informal speech and rounding off

In speaking, it is common to round the time to the nearest five minutes and/or express the time as the past (or to) the closest hour; for example, "five past five" (5:05). Minutes past the hour means those minutes are added to the hour; "ten past five" means 5:10. Minutes to, 'til and of the hour mean those minutes are subtracted; "ten of five", "ten 'til five", and "ten to five" all mean 4:50.

Fifteen minutes is often called a quarter hour, and thirty minutes is often known as a half hour. For example, 5:15 can be phrased "(a) quarter past five" or "five-fifteen"; 5:30 can be "half past five", "five-thirty" or simply "half five". The time 8:45 may be spoken as "eight forty-five" or "(a) quarter to nine".[14]

In older English, it was common for the number 25 to be expressed as "five-and-twenty".[15] In this way the time 8:35 may be phrased as "five-and-twenty to 9",[16] although this styling fell out of fashion in the later part of the 1900s and is now rarely used.[17]

Instead of meaning 5:30, the "half five" expression is sometimes used to mean 4:30, or "half-way to five", especially for regions such as the American Midwest and other areas that have been particularly influenced by German culture. This meaning follows the pattern choices of many Germanic and Slavic languages, including Serbo-Croatian, Dutch, Danish, Russian and Swedish, as well as Hungarian and Finnish.

Moreover, in situations where the relevant hour is obvious or has been recently mentioned, a speaker might omit the hour and just say "quarter to (the hour)", "half past" or "ten 'til" to avoid an elaborate sentence in informal conversations. These forms are often commonly used in television and radio broadcasts that cover multiple time zones at one-hour intervals.[18]

In describing a vague time of day, a speaker might say the phrase "seven-thirty, eight" to mean sometime around 7:30 or 8:00. Such phrasing can be misinterpreted for a specific time of day (here 7:38), especially by a listener not expecting an estimation. The phrase "about seven-thirty or eight" clarifies this.

Some more ambiguous phrasing might be avoided. Within five minutes of the hour, the phrase "five of seven" (6:55) can be heard "five-oh-seven" (5:07). "Five to seven" or even "six fifty-five" clarifies this.

Formal speech and times to the minute

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"O'clock" redirects here. For the o'clock watch, see O bag.

Minutes may be expressed as an exact number of minutes past the hour specifying the time of day (e.g., 6:32 p.m. is "six thirty-two"). Additionally, when expressing the time using the "past (after)" or "to (before)" formula, it is conventional to choose the number of minutes below 30 (e.g., 6:32 p.m. is conventionally "twenty-eight minutes to seven" rather than "thirty-two minutes past six").

In spoken English, full hours are often represented by the numbered hour followed by o'clock (10:00 as ten o'clock, 2:00 as two o'clock). This may be followed by the "a.m." or "p.m." designator, though some phrases such as in the morning, in the afternoon, in the evening, or at night more commonly follow analog-style terms such as o'clock, half past three, and quarter to four. O'clock itself may be omitted, telling a time as four a.m. or four p.m. Minutes ":01" to ":09" are usually pronounced as oh one to oh nine (nought or zero can also be used instead of oh). Minutes ":10" to ":59" are pronounced as their usual number-words. For instance, 6:02 a.m. can be pronounced six oh two a.m. whereas 6:32 a.m. could be told as six thirty-two a.m.

Confusion at noon and midnight

Time according to various conventions Device or style Midnight
Start of day Noon Midnight
End of day

Written 24-hour time	00:00	12:00	24:00
Digital watches	12:00 AM	12:00 PM
U.S. Government Publishing Office (1953)[19]	midnight[a]	noon 12 o'clock noon 12 m.	midnight 12:00 p.m.
U.S. Government Publishing Office (2000)[20]	midnight[a]	12 a.m. noon	12 p.m. midnight[a]
U.S. Government Publishing Office (2008)[21]	12 a.m. 12 midnight[a]	12 p.m. 12 noon	12 midnight[a]
Japanese legal convention[22]	0:00 a.m.	12:00 a.m.	12:00 p.m.
Japanese common usage[23]	0:00 a.m.	0:00 p.m. 12:00 a.m.	12:00 p.m.
Chicago Manual of Style[24]		noon 12:00 m.
Canadian Press,[25] UK standard[26]	Midnight	Noon	Midnight
Associated Press style[27]	—	noon	midnight
NIST[2]	midnight[b] 12:01 a.m.	noon	midnight[b] 11:59 p.m.
^ a b c d e These styles are ambiguous with respect to whether midnight is at the start or end of each day. ^ a b NIST recommends using 11:59 p.m. and 12:01 a.m. to disambiguate when needed.

It is not always clear what times "12:00 a.m." and "12:00 p.m." denote. From the Latin words meridies (midday), ante (before) and post (after), the term ante meridiem (a.m.) means before midday and post meridiem (p.m.) means after midday. Since "noon" (midday, meridies (m.)) is neither before nor after itself, the terms a.m. and p.m. do not apply.[2] Although "12 m." was suggested as a way to indicate noon, this is seldom done[24] and also does not resolve the question of how to indicate midnight.

The American Heritage Dictionary of the English Language states "By convention, 12 AM denotes midnight and 12 PM denotes noon. Because of the potential for confusion, it is advisable to use 12 noon and 12 midnight."[28]

E. G. Richards in his book Mapping Time (1999) provided a diagram in which 12 a.m. means noon and 12 p.m. means midnight.[29]

The style manual of the United States Government Printing Office used 12 a.m. for noon and 12 p.m. for midnight until its 2008 edition, when it reversed these designations[20][21] and then retained that change in its 2016 revision.[30]

Many U.S. style guides, and NIST's "Frequently asked questions (FAQ)" web page,[2] recommend that it is clearest if one refers to "noon" or "12:00 noon" and "midnight" or "12:00 midnight" (rather than to "12:00 p.m." and "12:00 a.m."). The NIST website states that "12 a.m. and 12 p.m. are ambiguous and should not be used."

The Associated Press Stylebook specifies that midnight "is part of the day that is ending, not the one that is beginning."[27]

The Canadian Press Stylebook[25] says, "write noon or midnight, not 12 noon or 12 midnight." Phrases such as "12 a.m." and "12 p.m." are not mentioned at all. Britain's National Physical Laboratory "FAQ-Time" web page[26] states "In cases where the context cannot be relied upon to place a particular event, the pair of days straddling midnight can be quoted"; also "the terms 12 a.m. and 12 p.m. should be avoided."

Likewise, some U.S. style guides recommend either clarifying "midnight" with other context clues, such as specifying the two dates between which it falls, or not referring to the term at all. For an example of the latter method, "midnight" is replaced with "11:59 p.m." for the end of a day or "12:01 a.m." for the start of a day. That has become common in the United States in legal contracts and for airplane, bus, or train schedules, though some schedules use other conventions. Occasionally, when trains run at regular intervals, the pattern may be broken at midnight by displacing the midnight departure one or more minutes, such as to 11:59 p.m. or 12:01 a.m.[31]

In Japanese usage, midnight is written as 午前0時 (0:00 a.m.) and noon is written as 午後0時 (0:00 p.m.), making the hours numbered sequentially from 0 to 11 in both halves of the day.

In literature

• In the George Orwell novel Nineteen Eighty-Four, Winston Smith describes a twelve-hour clock as "old-fashioned".[32]

See also

• 24-hour clock
• Clock position
• Date and time representation by country
• Decimal time
• Italian six-hour clock
• Midnight
• Muhurta
• Noon
• Pahar
• Thai six-hour clock

References

1. ^ a b "Time". The New Encyclopædia Britannica. Vol. 28. 1986. pp. 660 2a.
   "Time". Encyclopædia Britannica. Encyclopædia Britannica Online Library Edition. Retrieved 20 November 2013. The use of AM or PM to designate either noon or midnight can cause ambiguity. (subscription required) For different opinions on representation of midday and midnight, see #Confusion at noon and midnight
2. ^ a b c d "Times of Day FAQs". National Institute of Standards and Technology. 21 September 2016. Archived from the original on 21 September 2018. Retrieved 30 September 2018.
3. ^ Susan Addington (25 August 2016). "Modular Arithmetic". Archived from the original on 4 July 2008. Retrieved 28 November 2008.
4. ^ "The History of Clocks". 13 October 2008. Archived from the original on 13 October 2008. Retrieved 12 November 2017.
5. ^ "Berlin instruments of the old Eg.time of day destination". members.aon.at. Archived from the original on 15 November 2006. Retrieved 13 June 2006.
6. ^ "Early Clocks". A Walk Through Time. National Institute of Standards and Technology. 12 August 2009.
7. ^ National Library of Australia catalogue entry for Rider's British merlin: for the year of Our Lord God 1795. Printed for the Company of Stationers, and sold by R. Horsfield, at Stationers-hall, near Ludgate-street. 1795. Archived from the original on 22 May 2013.
8. ^ Lawrence Abrams (13 December 2012). "How to customize how the time is displayed in Windows". Bleeping Computer. Archived from the original on 29 October 2013. Retrieved 26 October 2013.
9. ^ "hora". Diccionario panhispánico de dudas (in Spanish). Archived from the original on 20 July 2011.
10. ^ a b Economist Style Guide (12th ed.). The Economist. 2018. p. 185. ISBN 9781781258316.
11. ^ Watson, James Robert. "A more efficient way to denote am or pm". Jim Watson professor of design. Retrieved 30 August 2022.
12. ^ Hacker, Diana, A Writer's Reference, six edition, Bedford, St Martin's, Boston, 2007, section M4-c, p.308.
13. ^ The Tongue and Quill (PDF). US Air Force. 27 May 2015. p. 356. Archived from the original (PDF) on 26 November 2020. Retrieved 26 October 2021. Air Force Handbook 33-337.
14. ^ "quarter". American Heritage Dictionary (3rd ed.). Boston: Houghton Mifflin. 1992. s.v. usage note at end of "quarter" entry.
15. ^ Dickens, Charles (1855). Little Dorrit. p. Chapter 27.
16. ^ Trudgill, Peter (17 May 2020). "Number five-and-twenty: A fading linguistic practice". The New European. Retrieved 13 October 2022.
17. ^ Swan, Michael. "Ask About English". BBC World Service. BBC. Retrieved 13 January 2021.
18. ^ "TVTimes magazine 21-27 May 1983 part1". TVTimes. 21–27 May 1983. Archived from the original on 18 October 2012. Retrieved 8 October 2019.
19. ^ "United States Government Printing Office Style Manual" (PDF). govinfo. U.S. Government Publishing Office. January 1953. pp. 152, 267. Archived (PDF) from the original on 5 September 2019. Retrieved 5 September 2019.
20. ^ a b "U.S. Government Printing Office Style Manual" (PDF). govinfo. U.S. Government Publishing Office. 2000. page 156. Archived (PDF) from the original on 5 September 2019. Retrieved 5 September 2019.
21. ^ a b "U.S. Government Printing Office Style Manual" (PDF). govinfo. U.S. Government Publishing Office. 2008. p. 271. Archived (PDF) from the original on 12 April 2019. Retrieved 5 September 2019.
22. ^ 午前１２時？ 午後０時？ [12 AM? or 0 PM?]. National Institute of Information and Communications Technology (in Japanese). 15 February 1989. Archived from the original on 6 June 2017. Retrieved 24 May 2017.
23. ^ 質問4-1）正午は午前12時？それとも、午後12時？ [Question 4-1) Is noon 12 a.m.? Or 12 p.m.?]. National Astronomical Observatory of Japan (in Japanese). Retrieved 19 January 2022.
24. ^ a b Chicago Manual of Style (17th ed.). University of Chicago Press. 2017. paragraph 9.38. ISBN 978-0-226-28705-8. Although noon can be expressed as 12:00 m. (m = meridies), very few use that form.
25. ^ a b The Canadian Press Stylebook (11th ed.). 1999. page 288.
26. ^ a b "National Physical Laboratory, FAQ-Time". Archived from the original on 3 March 2015. Retrieved 11 January 2015.
27. ^ a b Paula Froke, Anna Joe Bratton, Oskar Garcia, Jeff McMillan & Jerry Schwart, Eds., 54th ed., The Associated Press Stylebook and Briefing on Media Law, New York: Basic Books, June 2019, ISBN 978-1-5416-9989-2, s.v. noon, midnight, times.
28. ^ "AM". The American Heritage Dictionary of the English Language (Fifth ed.). 2011. Archived from the original on 9 January 2014.
29. ^ Richards, E. G. (1999). Mapping Time: the Calendar and its History. Oxford University Press. p. 289.
30. ^ "GPO Style Manual. 2016. p.236". govinfo.gov. 12 January 2017. Archived from the original on 17 March 2018. Retrieved 16 March 2018.
31. ^ "Cheshunt/Enfield Town to London Liverpool Street via Seven Sisters service Interim train timetables" (PDF). Abellio Greater Anglia London. 17 May 2015. pp. 7, 8. Archived from the original (PDF) on 26 May 2015.
32. ^ Orwell, George (22 February 2016). "Part 2, Chapter 4". Nineteen Eighty-four. South Australia: eBooks@Adelaide. p. 157. Retrieved 23 June 2021.

External links

• NIST FAQ on time
• 12am is noon in Japan

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