What's the difference between them?
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2023-08-07T06:29:28.050
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2023-08-07T12:34:18.070
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word-choice
What's the difference between ひる (noon) and ごご (afternoon)?
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](https://www.google.com/search?q=%E6%97%A5%E3%81%AE%E5%87%BA+%E6%9D%B1%E4%BA%AC+2023-08-09)
says 04:55.

[https://www.google.com/search?q=日の入+東京+2023-08-09](https://www.google.com/search?q=%E6%97%A5%E3%81%AE%E5%85%A5+%E6%9D%B1%E4%BA%AC+2023-08-09)
says 18:38.

[https://www.google.com/search?q=日の出+京都+2023-08-09](https://www.google.com/search?q=%E6%97%A5%E3%81%AE%E5%87%BA+%E4%BA%AC%E9%83%BD+2023-08-09)
says 05:12.

[https://www.google.com/search?q=日の入+京都+2023-08-09](https://www.google.com/search?q=%E6%97%A5%E3%81%AE%E5%85%A5+%E4%BA%AC%E9%83%BD+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](https://www.python.org/) 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](https://ja.wikipedia.org/wiki/%E5%8D%88%E5%89%8D%E3%81%A8%E5%8D%88%E5%BE%8C).)

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)](https://ja.wikipedia.org/wiki/24%E6%99%82%E5%88%B6).
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2023-08-07T11:17:26.820
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2023-08-07T11:17:26.820
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answer
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](https://www.jma.go.jp/jma/kishou/know/yougo_hp/saibun.html).
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2023-08-07T12:34:18.070
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2023-08-07T12:34:18.070
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answer