What is GMT Time?
GMT time is formally called Greenwich Mean Time and is the time that is found every day when the Sun passes the Prime Meridian in Greenwich, England. The mean time is the clock time as opposed to the solar time because the mean time is the average time. It is referred to as this way because solar time is not as accurate as mean time, due to seasonal differences across the world.
Every day, the solar time would be different, as the time the Sun passes that meridian will change by one or two minutes, depending on the area and the season. Mean time is measured in clock hours and minutes, which do not ever change. Twenty-four hours is one day, regardless of how long the sun has been out that day. This mean time allows the world to run on a standardized time system. Every other time zone is calculated using GMT, and then a plus or minus number beside it. So GMT +5 will be GMT time, plus five hours. GMT plus five-time zone is a time zone that is five hours east of GMT.
GMT was the official standardized unit of time until 1972, when it was replaced by UTC, or, Coordinated Universal Time. They are still the same units and easy to understand when interchanged with each other.
The History of Time Zones
The history of time zones began in 1650 when the pendulum was the clock. Sun dials were used and it was easy to determine an average or mean time alongside solar time. It was John Flamsteed that determined that solar time could be converted into a number that everybody would understand. By the 1670s, GMT was observed, and John Flamsteed became the first Royal Astronomer as a result.
The fifth Royal Astronomer Nevil Maskelyne took GMT to the world in the 1700s, and by 1767 it would become part of the Nautical Almanac and used across the world. He introduced the concept of using longitude as a means of calculating the GMT. This is when the first lunar tables were made and observations at Greenwich would define the new standard of time. The first reason this was developed was for those at sea, but it soon became a simplified solution to longitudinal time differences.
GMT 5 Countries
The GMT 5 countries that use GMT plus five hours are as follows: