Greenwich Mean Time or GMT is the time that is marked at the Prime Meridian when the sun crosses it. It is called this because the location of the Earth this occurs at is Greenwich, England. This time zone or timeline was in effect between 1884 and 1972, as a result of the plans set forth by Royal Astronomers.
The first to determine that a universal time zone or timeline was needed was John Flamsteed in the 1650s who learned that a formula could be established that would calculate the solar time into a relatable and English-term time. From this, he wanted the entire world to have a set and universal time zone where the world could understand what time it was in their own land.
This was not the first concept of time zones, because the Sun has been in a different position in different locations of the world since the beginning of time. It has always been night in some locations when it has not been in others, and it always will be. The GMT establishment was considered to make the time a more concrete principle.
At the time, railway was just expanding and a concrete time was critical. An international standard needed to be developed. By 1884, a conference known as the International Meridian Conference in Washington D.C. established the GMT as the world’s official time. Here, 22 countries passed the adoption of the Greenwich Mean Time and established it as the Prime Meridian. The GMT is still used today as the starting point for time zones.
Today, the GMT is used by the Met Office, the Royal Navy, the BBC World and many other key figures throughout the world.
The terms GMT and UCT are used interchangeably and mean the same thing. Greenwich Mean Time is the time at the Prime Meridian, and UTC is Coordinated Universal Time. UTC was established in 1972 to replace the GMT with a more modern timeline of the world. Most experts and policy makers then thought this was a more accurate way of keeping time than using the GMT was.
The UTC uses what are called atomic clocks that clocks leap seconds in order to make up for any discrepancies in world time. Still, many people use GMT today.
The countries in the GMT 9 times will have the time of GMT plus nine hours. Those countries are as follows:
Japan, Russia, North Korea, South Korea, Indonesia, and Timor are all countries that are in GMT +9.