Why is the Greenwich Meridian the reference meridian?

First of all, what is a meridian, where does it come from and what is it used for?
We reveal all these secrets to you in this article.

The origin of time zones

The idea of ​​dividing the Earth into such lines dates back to ancient civilizations, particularly the Greeks. The Greek geographer Hipparchus (c. 190–120 BC) is credited with his early attempts to divide the Earth into a grid using lines of latitude and longitude.

Before a standard was installed worldwide, each city had a different time. In fact, we still relied on the sun to know the local time, which was also called “Local Solar Time”.

So each city had a slightly different time, it could be very difficult for example to coordinate trains!

Greenwich Mean Time

In 1884, an international conference in Washington DC established the meridian passing through Greenwich, England, as the world prime meridian. This decision was largely influenced by British naval dominance and the widespread use of Greenwich Mean Time (GMT) in navigation and commerce.

Greenwich was thus at latitude 0, which makes it the reference point for time zones. In France, according to summer and winter time, we are between UTC +1 and +2.

How does this system work?

24 time zones have been created, the earth is round so logically, each meridian is separated by 15 degrees from the south pole to the north pole.

So, between each meridian, this imaginary line, a time zone is referred to. If a state or country crosses several time zones, it is free to either keep only one time zone or to have several.

For example, China, although it crosses several time zones, has only one official time, unlike the United States, which has several time zones depending on its states.

The influence of this concept in watchmaking?

The Greenwich Meridian is essential in so-called "GMT" or "dual time" watches. These watches allow two time zones to be displayed at the same time, often by using an additional hand to indicate the time on the Greenwich Meridian, while displaying the local time.

Our Jules automatic watch uses an internal bezel that allows it to display the time in a second time zone around the Earth.