Dates in Japanese Era Names in Unicode Standard

Philippe Verdy verdy_p at
Thu Sep 29 05:06:22 CDT 2016

Is it possible that these eras start at midday instead of noon ? This could
explain the date difference, if you do not set the time in your query (your
query will assume a default time at 00:00 midnight)

There's a similar issue with most calendars before the modern Gregorian,
and even within historic documents still using date shifting at midday (and
then naming the morning with the previous day). This practice survided for
long as physical 24-hour clocks were rare. Still today, many
English-speaking countries use AM/PM periods and 12-hour clocks are used
for almost all non-electronic displays (even if some watches also include a
small circle display a 24-clock, the 12-hour display is the most common and
the easiest to read (it is a partial survival of the old Roman calendar
that counted time negatively relative to the date defined clearly at
midday, because midday is more more easily observable with a good precision
than midnight).

The recent introduction of daylight saving (and generalization of official
times in large timezones) changed the perception of clock, as it was no
longer synchronized with observation of the Sun. Negative counting in dates
and time as now almost disappeared (except in popular language for counting
the last minutes relative to hours, a correct form of precision rounding).
Dates are better understood to cover the whole working day (or rest day),
except for religious purpose (e.g. withing Judaism, whose reference is the
variable time of sun fall in the evening, or in Islam with also a variable
reference time at sunrise as observed in a reference location determined by
local or national communities).

Many people still count the second half of the night after midnight as part
of the previous day (and so will say "Saturday evening"/"Saturday night"
even if it's already the first hours of Sunday).

If you test dates and don't want to specify hours, it is highly recommended
to set the default time at midday. For the Japanese eras, it's not clear at
which time they really start, except for the last two eras since WW2 but
setting time at midday shoudl give the correct result. However there's no
ambiguity during the day of era switch, if the era is correctly specified
(and not just the year number in era).

2016-09-29 5:13 GMT+02:00 Junichi Chiba <junichi.chiba.bps at>:

> Dear all,
> Nice to e-meet you.
> I'm looking at the latest Unicode Standard [1] listing the dates for
> Japanese Era Names in Table 22-8.
> What I noticed is the begin and end dates for each era.
> They seem to have one day difference with the dates that are recognized
> publicly in Japan.
> For example, the current Heisei actually started January 8th, 1989, after
> Showa ended on 7th, 1989.
> However, the Unicode Standard says in Table 22-8:
> U+337B square era name heisei 1989-01-07 to present day
> U+337C square era name syouwa 1926-12-24 to 1989-01-06
> Looking at Wikipedia in Japanese [2] and English [3], you can see exact
> dates for Syouwa end and Heisei start.
> Could there be certain intentions to leave some difference in this
> description and official dates?
> Is the date counted according to GMT, instead of local date/time for some
> reason?
> [1]
> [2]
> > 1989年(昭和64年)1月7日に昭和天皇が崩御して、皇太子明仁親王が即位した(今上天皇)。これを受け、元号法に基づき1989年(昭和64年)
> 1月7日に元号法に基づき改元の政令がだされ、「平成元年1月8日」と改元がなされた。
> [3]
> > Thus, 1989 corresponds to Shōwa 64 until 7 January and Heisei 1 ...
> since 8 January.
> > On 7 January 1989, at 07:55 JST, the Grand Steward of Japan's Imperial
> Household Agency, Shōichi Fujimori, announced Emperor Hirohito's death,...
> > The Heisei era went into effect immediately upon the day after Emperor
> Akihito's succession to the throne on 7 January 1989.
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