The Global Timekeeping System: Time Zones Explained
II. The Universal Timekeeping Method: The Time Zone System
(I) Shichen β Ancient Chinese Time Units
In ancient China, a day was divided into 12 shichen (ζθΎ°), each represented by one of the 12 Earthly Branches. Each shichen is equivalent to 2 modern hours. Table 1β1β2 below shows the correspondence between ancient and modern time.
| Ancient Time (Shichen) | Modern Hours | Ancient Time (Shichen) | Modern Hours |
|---|---|---|---|
| Zi ε | 23:00 β 01:00 | Chou δΈ | 01:00 β 03:00 |
| Yin ε― | 03:00 β 05:00 | Mao ε― | 05:00 β 07:00 |
| Chen θΎ° | 07:00 β 09:00 | Si ε·³ | 09:00 β 11:00 |
| Wu ε | 11:00 β 13:00 | Wei ζͺ | 13:00 β 15:00 |
| Shen η³ | 15:00 β 17:00 | You ι | 17:00 β 19:00 |
| Xu ζ | 19:00 β 21:00 | Hai δΊ₯ | 21:00 β 23:00 |
(II) Time Zones
Before the establishment of the time zone system, clocks around the world had no unified standard. It is said that in 1880, Buffalo Railway Station in New York State had three clocks: one showing local Buffalo time, one showing New York City time, and one showing Omaha, Nebraska time. The resulting confusion was considerable.
In 1879, Canadian railway engineer Sandford Fleming first proposed the concept of worldwide "time zones." In 1883, the American Railway Association convened a conference and decided to divide the country into 4 time zones, each differing by 1 hour β the earliest time zone system in history.
In 1884, at the International Prime Meridian Conference held in Washington D.C., it was decided to extend the time zone system to the entire world.
(III) The Time Zone System
1. The Zero Time Zone
Starting from the Prime Meridian passing through the Royal Observatory in Greenwich, England, the zero time zone extends 7Β°30β² to the east and 7Β°30β² to the west, spanning a total of 15Β°, with the Prime Meridian as its central meridian. East Time Zone 1 spans from 7Β°30β²E to 22Β°30β²E, with 15Β°E as its central meridian. West Time Zone 1 spans from 7Β°30β²W to 22Β°30β²W, with 15Β°W as its central meridian. And so on. It is worth noting that East Time Zone 12 and West Time Zone 12 overlap.
2. The Time Zone System (Figure 1β1β13)
Every 15Β° of longitude on Earth constitutes one time zone β the distance the sun travels in one hour. This divides the entire surface of the Earth into 24 time zones. The time zone system has largely resolved the confusion of local times around the world, ensuring that only 24 distinct times exist globally at any given moment. Furthermore, since adjacent time zones differ by exactly 1 hour, converting between any two time zones becomes extremely straightforward.
For over 100 years, this system has been used continuously by people around the world.
Time Zones and the Watches That Cross Them
The time zone system transformed how humanity coordinates across distance β and the finest watches have always been built to keep pace with a world in motion. Whether you are crossing continents or simply appreciating the craft of precision timekeeping, explore our collections at Aorawa Time.