Why Japan runs on a single meridian
When Yokohama’s port opened to foreign trade in 1859, the city kept its own time. Clocks were set by the sun. Noon in Yokohama was 11:55 in Tokyo and 11:48 in Osaka. That worked for centuries. Then came the railway.
Japan’s first railway opened between Shimbashi and Yokohama in 1872. Timetables listed departure times for each station in that station’s local time. Passengers missed connections. Freight schedules conflicted. The system could not scale. A nation that had organized itself around feudal domains now needed to run on a single clock.
The port that forced the issue
Yokohama’s foreign settlement had used local solar time for 27 years. Ship captains arriving from San Francisco or Shanghai calculated the local Yokohama time from their chronometers. Every Japanese port had a different offset. For a country trying to industrialize, this was untenable.
Why local time died
Railways made the problem urgent. But the deeper driver was the Meiji government’s modernisation programme. A unified time standard was essential for military coordination, factory schedules, and alignment with Western trading partners. Japan did not ease into it. It legislated one time for the whole country in a single ordinance.
How the 1886 ordinance created Japan Standard Time
On 12 July 1886, the Meiji government issued Imperial Ordinance No. 51. It established a single national time for Japan. The rule was straightforward: all of Japan would follow the time at 135° east longitude.
Why 135°E? The International Meridian Conference in 1884 had established Greenwich as the prime meridian. Time zones were proposed in 15° increments, each one hour apart. 135°E is exactly 9 hours ahead of Greenwich. It also passes through the city of Akashi, in Hyōgo Prefecture, roughly in the middle of Japan’s main island of Honshu.
The 1888 switchover
The ordinance took effect on 1 January 1888. On that day, every clock in Japan was set to Japan Standard Time, UTC+9. The meridian line at 135°E became the official reference.
Akashi and the meridian monument
Akashi built a monument marking the line. The city still promotes itself as “the town of time.” The Akashi Municipal Planetarium displays the meridian marker. It is a popular photo spot for Japanese school groups.
What changed at Yokohama port
After 1888, ship captains simply added 9 hours to Greenwich Mean Time. The new system made Yokohama’s shipping schedules consistent with every other Japanese port. Customs procedures, which had been a tangle of local times, became uniform overnight.
Japan’s brief experiment with two time zones
When Japan annexed Taiwan in 1895, it briefly applied a western standard time (UTC+8) to the colony. This created a two-zone system within the Japanese Empire.
That arrangement did not last. By 1937, Taiwan was moved to Japan Standard Time (UTC+9) to align with military and administrative needs. Taiwan returned to UTC+8 after World War II. Japan itself has never returned to a multi-zone system.
Why Japan tried daylight saving and then killed it
Under the Allied occupation after World War II, Japan experimented with daylight saving time. The Supreme Commander for the Allied Powers ordered the change as part of a broader effort to reshape Japanese society.
From 1948 to 1951, Japan observed “summer time” (サマータイム). Clocks moved forward one hour on the first Sunday in May and back on the second Saturday in September. The change was unpopular from the start.
Farmers and the cows that ignored the clock
Farmers led the opposition. Milking schedules and crop routines were tied to the sun, not the clock. Cows did not adjust. Agricultural groups lobbied hard against the change.
Schools and the dark mornings
Educators complained that children walked to school in the dark during the early weeks of the summer time period. Parents worried about road safety. The concern was not abstract: Japan’s narrow streets and early school start times made darker mornings a genuine risk.
The office workers who worked longer
Office workers disliked the longer evening hours. They felt the change extended their workdays rather than saving energy. The cultural norm of staying until the boss leaves meant later sunsets simply pushed quitting time later.
In 1951, after the occupation ended, the Japanese Diet abolished the summer time law. Japan has not observed daylight saving since.
The 1970s and 2000s debates that went nowhere
The 1970s oil crisis prompted a brief reconsideration. The government studied reintroducing DST as an energy-saving measure. The idea died in committee.
In the 2000s, the Ministry of Economy, Trade and Industry (METI) conducted a detailed study. It estimated that reintroducing DST would reduce electricity consumption by only 0.1 to 0.2 percent. The savings were too small to justify the disruption.
The work-life balance counterattack
Opposition from work-life balance advocates was particularly effective. They argued that later sunsets would encourage Japanese companies to demand longer working hours, not shorter ones. The energy savings would be eaten up by air conditioning running longer in the evening. No legislation passed. None is pending.
Who keeps Japan Standard Time accurate today
Japan’s time standard is maintained by the National Institute of Information and Communications Technology (NICT). NICT operates atomic clocks at its headquarters in Koganei, Tokyo. These clocks are part of the International Atomic Time network.
How the signal reaches Yokohama
NICT broadcasts the time via radio signals (JJY) and through the internet. Devices across Japan, from train control systems to office clocks, sync to NICT’s signal.
Leap seconds and international coordination
Japan follows international leap-second adjustments coordinated by the International Earth Rotation and Reference Systems Service. NICT applies these adjustments to keep Japan Standard Time within 0.9 seconds of universal time. Yokohama gets the same adjustments as every other city in the country. There is no separate municipal time authority.
What JST history means for Yokohama in 2026
Yokohama remains on Japan Standard Time, UTC+9, all year. There are no clock changes in spring or autumn.
Daylight swings across the seasons
The daylight hours shift dramatically across the year. On the June solstice (21 June 2026), sunrise is at 04:26 and sunset at 18:59, giving 14 hours 33 minutes of daylight. On the December solstice (21 December 2026), sunrise is at 06:46 and sunset at 16:32, giving 9 hours 46 minutes of daylight.
The IANA zone
The city’s time zone is Asia/Tokyo in the IANA time zone database. Yokohama shares this zone with all of Japan. No separate zone exists for the city.
Quick reference: Japan Standard Time milestones
| Year | Event |
|---|---|
| 1886 | Imperial Ordinance No. 51 establishes unified national time |
| 1888 | Meridian set at 135°E through Akashi; JST takes effect |
| 1895 | Taiwan annexed; briefly uses UTC+8, later moved to JST |
| 1948-1951 | Daylight saving time observed under occupation |
| 1951 | DST abolished; Japan returns to year-round JST |
| 2000s | METI study estimates 0.1-0.2% electricity savings from DST; no action taken |
| Present | NICT maintains atomic clocks; no DST; UTC+9 year-round |
For more on why Japan does not change its clocks, see Daylight Saving Time in Yokohama. For the full list of Japanese holidays and how they affect business hours, see Japan Public Holidays 2026. For the current time in Yokohama and the Asia/Tokyo zone, see Yokohama Time Zone.