Why Japan picked 135°E for its standard meridian
A clock in the port city told a different story than a clock in Kyoto. Every town used local solar time: noon was the moment the sun hit its highest point. Because the sun moves east to west, a city one degree of longitude east of another sees noon about four minutes earlier.
Yokohama sits at 139.65°E. Tokyo is nearby. Their solar times were nearly identical. But Nagasaki, far to the west, ran about 39 minutes behind. This worked fine when travel took days and telegraphs did not exist. It became a problem when Japan opened to international trade.
Why local time broke down
Railways could not run a single timetable. Telegraph offices could not log messages with a common timestamp. A merchant in Yokohama arranging a shipment to Kobe had to calculate the time difference manually. The Meiji government saw unified time as essential to building a modern state.
How a treaty port forced the issue
Yokohama was one of the first treaty ports opened under the 1858 Treaty of Amity and Commerce. Foreign merchants, consuls and shipping lines arrived from Britain, the United States, France and the Netherlands. These ships ran on schedules tied to Greenwich Mean Time. Local solar time in the port was close enough to what became JST, but it was not standardised. Port operations, customs clearances and telegraph messages all suffered from the mismatch.
The need for a single national time became urgent after the Meiji Restoration. The government wanted a modern railway network, a unified postal system and a telegraph service that could transmit accurate times across the country.
The 1886 ordinance and the 1888 unification
On 28 July 1886 (Meiji 19), the government issued Imperial Ordinance No. 51, the Act on the Calculation of Dates and Times. It declared that Japan would adopt a standard meridian for timekeeping. The effective date: 1 January 1888.
The chosen meridian was 135°E. Why 135°E and not a line through Tokyo? Geometry. 135°E is exactly 9 hours ahead of UTC (then Greenwich Mean Time). It falls neatly in the middle of the UTC+9 time zone band. The 135th meridian also passes through the city of Akashi, in Hyōgo Prefecture. Akashi still markets itself as the "City of the Standard Meridian" and operates a museum on the line.
The 1888 switch was not a small adjustment. For Yokohama, it meant shifting clocks forward by about 18 minutes to match 135°E solar noon. For Nagasaki, the jump was nearly 57 minutes.
The 1895 formalisation
The 1886 ordinance set the meridian. A follow-up ordinance in 1895 (Meiji 28) formally established 135°E as the "standard meridian of Japan". This is the legal foundation that remains in force today. The 1895 law also confirmed that Japan would not observe any half-hour or quarter-hour offsets. The time would be a whole number of hours from Greenwich.
How Japan kept time before atomic clocks
In the early Meiji era, accurate timekeeping relied on astronomical observatories. The Tokyo Astronomical Observatory (now part of the National Astronomical Observatory of Japan) determined the precise moment of solar noon using a transit telescope. It then telegraphed the time to railway stations, post offices and the port authority.
Telegraph signals and radio beeps
The first electronic time signal came from the Tokyo Central Telegraph Office, which began sending time pulses over telegraph lines in the 1890s. By 1925, NHK (Nippon Hōsō Kyōkai) started broadcasting a daily radio time signal. Listeners across Japan could hear the beep at noon and set their clocks.
The telephone time service
The telephone time service (dial 117) began later and still operates today. Pick up any phone in Japan, dial 117, and hear the current JST announced in Japanese.
Why a single zone for a country spanning 24 degrees of longitude?
Japan stretches far enough east to west to fit two standard time zones. During the Allied occupation after World War II, the possibility of splitting Japan into eastern and western zones was discussed but never implemented. The argument against it was practical: a single time zone kept the railway network, broadcasting and government administration simple. The argument for it was that sunrise in Okinawa comes about an hour earlier than in Tokyo, and in winter that means workers in western Japan start their day in darkness.
Debates resurface every few decades. In the 2000s, Hokkaido and Okinawa local governments raised the idea of a dual-zone system to improve quality of life. No legislation has ever been introduced.
The solar noon gap
Yokohama solar noon is roughly 11:42 JST, not 12:00. This is normal for the eastern edge of a time zone. The clock runs slightly behind true solar time compared to western Japan. Visitors from the western edges of their own time zones often find sunrise and sunset feel early.
The 1948-1951 daylight saving experiment
Japan tried daylight saving time for four years under the Allied occupation. From 1948 to 1951, clocks moved forward one hour in summer. The experiment was deeply unpopular. Farmers objected because livestock and crops do not follow clocks. Mothers complained that children went to school in the dark. Workers saw it as an extension of the workday without extra pay. When Japan regained sovereignty in 1952, the first Diet session abolished DST. It has never returned.
The post-Fukushima DST debate
The 2011 energy crisis after the Fukushima disaster briefly revived the discussion. The Ministry of Economy, Trade and Industry studied DST for energy savings. The conclusion: IT system costs, lifestyle disruption and negligible energy benefit made it unworkable. No current legislative proposals exist. DST remains politically dormant.
A deeper look at the DST debate is covered on the Daylight Saving Time page.
Atomic clocks, NICT and the JJY signal
Japan Standard Time is now maintained by the National Institute of Information and Communications Technology (NICT). NICT operates a cluster of caesium atomic clocks at its headquarters in Koganei, Tokyo. These clocks generate a time scale accurate to within a few billionths of a second per day.
How JST reaches Yokohama
NICT distributes JST through three channels.
NTP servers. Public Network Time Protocol servers at ntp.nict.jp allow computers and servers to synchronise.
JJY radio signal. Two longwave transmitters broadcast the official time. The main station is on Mount Otakadoya in Fukushima Prefecture, transmitting at 40 kHz. A backup station on Mount Hagane in Kyūshū transmits at 60 kHz. Radio-controlled clocks sold in Japan receive JJY and set themselves automatically.
Telephone service. Dial 117 from any Japanese phone to hear the current JST announced in Japanese.
The IANA time zone identifier for all of Japan is Asia/Tokyo. There is no separate zone for Yokohama or any other city. The current time in Yokohama is on the Time Zone page.
Gregorian dates, Reiwa years and the calendar Japan actually uses
Japan uses the Gregorian calendar for all civil purposes. The imperial era year system, Reiwa 8 for 2026, is still used on government documents, driver's licences and some business forms. The current era, Reiwa (令和), began on 1 May 2019.
Some traditional contexts use the lunar calendar for festivals. Obon dates vary by region. In Yokohama, Obon is typically observed in August. Confirm with local ward offices for specific dates.
Key dates in JST history
| Year | Event |
|---|---|
| 1859 | Yokohama opens as a treaty port; local solar time used for shipping |
| 28 July 1886 | Imperial Ordinance No. 51 declares standard time to begin 1 January 1888 |
| 1 January 1888 | Japan adopts 135°E meridian (UTC+9) as unified standard time |
| 1895 | Ordinance formally establishes 135°E as the standard meridian |
| 1925 | NHK begins broadcasting daily radio time signal |
| 1948-1951 | Daylight saving time observed during Allied occupation |
| 1952 | DST abolished after sovereignty restored |
| 1960s, present | NICT (formerly CRL) maintains JST with atomic clocks |
| 1999 | JJY longwave time signal begins from Mount Otakadoya (40 kHz) |
| 2001 | JJY backup station begins from Mount Hagane (60 kHz) |
| 2011-2012 | Post-Fukushima DST study concludes costs outweigh benefits |
| Present | JST = UTC+9, no DST, single time zone, maintained by NICT |
For a full list of Japan's public holidays in 2026 and 2027, see the Japan Public Holidays page. For business hours and the daily rhythm of Yokohama, see the Business Hours guide.