Time is important all over the world, but not many people know how its standard is determined. This article explains what “standard time” is, how Japan’s standard time is set, time differences with other countries, the International Date Line, and the global system of time in an easy-to-understand way.
What Is Standard Time?
“Standard time” refers to the official basis of time used in a country or region.
Since the Earth rotates once every 24 hours, the entire globe is divided into 24 “time zones” every 15 degrees of longitude. This allows local times to be adjusted so that sunrise and sunset align with daily life in each area.
World Standard Time and Coordinated Universal Time (UTC)
The basis of world time today is Coordinated Universal Time (UTC). It is derived from the former Greenwich Mean Time (GMT), which was based on the prime meridian (0° longitude) passing through the Royal Observatory in Greenwich, near London.
Each country sets its own standard time by adding or subtracting hours from UTC.
Examples:
- London: UTC±0 (UTC+1 during daylight saving time)
- Paris: UTC+1 (UTC+2 during daylight saving time)
- New York: UTC-5 (UTC-4 during daylight saving time)
- Sydney: UTC+10 (UTC+11 during daylight saving time)
Japan Standard Time (JST)
Japan’s standard time is called Japan Standard Time (JST), which is UTC+9.
In other words, when it is 9:00 a.m. in Japan, it is 0:00 midnight in London (1:00 a.m. during daylight saving time). Japan uses a single time zone nationwide, so the same time is applied from Hokkaido to Okinawa.
Japan Standard Time is based on the 135° east meridian, which passes through Akashi City in Hyogo Prefecture. The city is also known as “the home of Japan Standard Time.”
The International Date Line
The “International Date Line” is the global boundary where calendar dates change. It runs mainly through the Pacific Ocean, roughly along the 180° longitude.
On the west side of this line, the date advances by one day, while on the east side, it lags by one day. For example, when flying eastward from Japan to Hawaii, the calendar date moves back by one day. Conversely, moving westward advances the date.
The line zigzags to account for national borders and islands, so it is not a straight line along 180° longitude.
What Is a Time Difference?
A time difference refers to how much the local time in one region differs from that in another. For example, Japan (UTC+9) has a 9-hour difference from London (UTC±0).
Time differences are important in situations such as:
– Overseas travel or international calls
– Live broadcasts of international sports or events
– International meetings and online conferences
Many countries use daylight saving time (summer time), advancing clocks by one hour in summer to make better use of daylight. Japan does not use daylight saving time.
Time Differences Between Major Cities and Japan
Here is a table summarizing Japan’s time differences with major cities (without daylight saving time).
| City | Country | Difference from Japan | Local Time When It’s Noon in Japan |
|---|---|---|---|
| London | United Kingdom | -9 hours | 3:00 a.m. |
| Paris | France | -8 hours | 4:00 a.m. |
| New York | United States | -14 hours | 10:00 p.m. (previous day) |
| Los Angeles | United States | -17 hours | 7:00 p.m. (previous day) |
| Sydney | Australia | +1 hour | 1:00 p.m. |
| Seoul | South Korea | 0 hours | Noon (same) |
| Beijing | China | -1 hour | 11:00 a.m. |
| Bangkok | Thailand | -2 hours | 10:00 a.m. |
| Dubai | United Arab Emirates | -5 hours | 7:00 a.m. |
*In cities that use daylight saving time, the time difference changes depending on the season.
Understanding Time Differences Brings the World Closer
Knowing about time differences makes international communication smoother. For example, if a Japanese company schedules a meeting at 9:00 a.m. with a partner in the UK, it would be midnight there. Choosing considerate times requires an understanding of these differences.
Similarly, when checking schedules for international sports tournaments or news broadcasts, knowledge of time differences is very useful.
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