UTC (Coordinated Universal Time)
utc
The primary time standard by which the world regulates clocks and time, serving as the basis for civil timekeeping globally.
JST (Japan Standard Time)
jst
Overview
JST (Japan Standard Time) is the time standard used throughout Japan, fixed at 9 hours ahead of UTC (UTC+9). In the IANA Time Zone Database it is identified as Asia/Tokyo. The reference meridian is 135 degrees east longitude, which passes through the city of Akashi in Hyogo Prefecture, and the entire country observes a single unified time zone.
Historical Background
Japan Standard Time was established in 1886 by Imperial Ordinance No. 51. The 135th meridian was chosen because it is an exact multiple of 15 degrees, yielding a clean offset of exactly 9 hours from UTC. An alternative proposal based on Tokyo's longitude (approximately 139.7 degrees east) was rejected because it would have produced an awkward offset of 9 hours, 18 minutes, and 58 seconds.
No Daylight Saving Time
Japan briefly observed daylight saving time from 1948 to 1951 under Allied occupation, but public dissatisfaction led to its abolition. Although reintroduction was discussed as recently as 2018 as a heat-mitigation measure for the Tokyo Olympics, it was never implemented. Because JST remains UTC+9 year-round, programmers working with Japanese time data do not need to handle DST transitions, making it one of the simpler time zones to work with in software.
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Related Terms
Time Zone
timezone
A region of the globe that observes a uniform standard time for legal, commercial, and social purposes.
Meridian
meridian
A meridian is an imaginary semicircle running from the North Pole to the South Pole on the Earth's surface, serving as a reference line for longitude and forming the foundation of the global timekeeping system.
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