Japan standard time

Japan Standard Time (日本標準時 or 中央標準時) is the standard timezone in Japan that is 9 hours ahead of UTC; i.e. when it is midnight (00:00) in UTC, it is 9 am (09:00) in Japan Standard Time.

Before Meiji Era, each local region had been using a timezone in which the noon was set when the Sun is exactly at South. As modern transportations like train were adopted, this practice started to cause confusions. For example, there is a difference of about 5 degrees in terms of longitude between Tokyo and Osaka and because of this, a train that departed Tokyo would arrive at Osaka at 20 minutes ahead of the time in Tokyo. In 1886 (Meiji 19), a chokurei (Imperial Ordinance was issued in response to this, which states:

明治十九年勅令第五十一号（本初子午線経度計算方及標準時ノ件）
（明治十九年七月十三日勅令第五十一号）

• 英国グリニツチ天文台子午儀ノ中心ヲ経過スル子午線ヲ以テ経度ノ本初子午線トス
• 経度ハ本初子午線ヨリ起算シ東西各百八十度ニ至リ東経ヲ正トシ西経ヲ負トス
• 明治二十一年一月一日ヨリ東経百三十五度ノ子午線ノ時ヲ以テ本邦一般ノ標準時ト定ム

According to this, the standard time (標準時) was set 9 hours ahead of GMT (UTC was not established yet.) In the ordinance, the first clause mentions about GMT, the second defines east longitude and west longitude and the third says the standard timezone would be in effect from 1888. Coincidentally, a city of Akashi in Hyogo prefecture is located exactly on 135 degrees east longitude and the city subsequently has become known as Tokino machi (town of time).

With annexation of Taiwan in 1895, Western Standard Time (西部標準時) was defined with 120° longitude, and the previous Standard Time was renamed to Central Standard Time (中央標準時). (See the picture on the right.) Western Standard Time was used in Taiwan and some part of Okinawa, until 1937.

Japan Standard Time is the same as Korea Standard Time.

Reference

• 日本標準時子午線制定の日 - this is a cached page by Google; the original site seems dead, unfortunately.

See also: Timezone, GMT, UTC

See also: Japan standard time, 1886, 1888, 1895, 1937, Akashi, East longitude, GMT, Google, Hyogo prefecture