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What's the difference between them?

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  • en.wikipedia.org/wiki/Noon has 2 definitions of noon: traditional and scientific ("Solar noon is the time when the Sun appears to contact the local celestial meridian. This is when the Sun reaches its apparent highest point in the sky, at 12 noon apparent solar time and can be observed using a sundial. The local or clock time of solar noon depends on the longitude and date, with Daylight Saving Time tending to place solar noon closer to 1:00pm.")
    – Arfrever
    Aug 7, 2023 at 7:14
  • 2
    Do you understand the difference between noon and afternoon? Aug 7, 2023 at 10:09
  • ごご is used for expressions that specify a time with a number; ひる itself already describes an approximate time (it's the time when you eat 昼ご飯). Aug 7, 2023 at 13:53
  • Just to avoid repeating what you already know, what have you found so far? If you've looked in dictionaries and still can't figure it out, please show your research effort and include as much context as you can.
    – chocolate
    Aug 8, 2023 at 3:10

2 Answers 2

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昼(ひる)means midday or daytime. 午前(ごぜん)means AM and 午後(ごご)means PM or, colloquially, afternoon (as in English). 正午(しょうご) means exactly noon. News and government documents use stricter guidelines. Here is a chart from the Japanese Meteorological Agency.

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Colloquially, 昼{ひる} is the time 12:00 in official timezone of given place.

Scientifically, 昼{ひる} is the time when Sun reaches its apparent highest point in the sky (its zenith). It is approximately in the middle of time between 日{ひ}の出{で} ("Sunrise") and 日{ひ}の入{いり} ("Sunset").

We can ask Google to tell us 日{ひ}の出{で} and 日{ひ}の入{いり}. Example for 東{とう}京{きょう} and 京{きょう}都{と} on 2023-08-09:

https://www.google.com/search?q=日の出+東京+2023-08-09 says 04:55.

https://www.google.com/search?q=日の入+東京+2023-08-09 says 18:38.

https://www.google.com/search?q=日の出+京都+2023-08-09 says 05:12.

https://www.google.com/search?q=日の入+京都+2023-08-09 says 18:53.

(This feature of Google also works with terms in other languages, e.g. English "sunrise" and "sunset".)

We can use Python to calculate 昼{ひる} in those cities on that day:

>>> import datetime
>>> 日の出_東京 = datetime.datetime(2023, 8, 9, 4, 55)
>>> 日の入_東京 = datetime.datetime(2023, 8, 9, 18, 38)
>>> 日の出_京都 = datetime.datetime(2023, 8, 9, 5, 12)
>>> 日の入_京都 = datetime.datetime(2023, 8, 9, 18, 53)
>>> 秒間_東京 = 日の入_東京 - 日の出_東京
>>> 秒間_京都 = 日の入_京都 - 日の出_京都
>>> 秒間_東京
datetime.timedelta(seconds=49380)
>>> 秒間_京都
datetime.timedelta(seconds=49260)
>>> 昼_東京 = 日の出_東京 + 秒間_東京 / 2
>>> 昼_京都 = 日の出_京都 + 秒間_京都 / 2
>>> 昼_東京
datetime.datetime(2023, 8, 9, 11, 46, 30)
>>> 昼_京都
datetime.datetime(2023, 8, 9, 12, 2, 30)

So:

  • 昼{ひる} in 東{とう}京{きょう} will be approximately on 2023-08-09 11:46:30.

  • 昼{ひる} in 京{きょう}都{と} will be approximately on 2023-08-09 12:02:30.


午{ご}後{ご} is used when specifying time in traditional 12-hours system (12時間制). (See also here.)

午{ご}前{ぜん}[8]{はち}時{じ} = 08:00 (in 24-hours system) = 08:00 [A.]{ante}[M.]{meridiem} (in 12-hours system)

午{ご}後{ご}[8]{はち}時{じ} = 20:00 (in 24-hours system) = 08:00 [P.]{post}[M.]{meridiem} (in 12-hours system)

Japan also has modern 24-hours system (24時制).

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  • 1
    I'd say colloquially, 昼 is not noon but some time around 11:00 - 14:00. 正午 specifically refers to 12:00.
    – sundowner
    Aug 7, 2023 at 11:53
  • Sometimes, 'お昼' can mean lunch time, and can also mean exact noon. :-)
    – MNEMO
    Aug 9, 2023 at 3:08

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