Greenwich Mean Time (GMT) is more than just a time zone; it’s a foundational concept in global timekeeping. But What Time Is It In Gmt right now? GMT doesn’t actually change with seasons like some time zones, so it remains consistent throughout the year. To know the precise time in GMT, you can check a world clock or time zone converter online, which will instantly tell you the current GMT time.
But to truly understand GMT’s importance, it’s essential to delve into its history and role in shaping our modern concept of time. Located at the Royal Observatory Greenwich in London, GMT’s story is intertwined with navigation, railways, and the very standardization of time itself.
Understanding Greenwich Mean Time
GMT is defined as the yearly average, or “mean,” time when the sun crosses the Prime Meridian at the Royal Observatory Greenwich. This might sound complex, but essentially, GMT represents clock time rather than solar time.
Solar time isn’t constant; the interval between the sun crossing a specific meridian line varies throughout the year. Clocks, however, measure time in consistent 24-hour days, based on the average length of a solar day. This standardization is crucial for everyone to have a common understanding of time, regardless of location. Today, GMT is measured from midnight to midnight.
Find out about the Prime Meridian
GMT vs. UTC: What’s the Difference?
While GMT was the international standard of civil time from 1884 to 1972, it has since been superseded by Coordinated Universal Time (UTC). Despite this change, GMT remains relevant. It is still the legal time in the UK during winter and is used by organizations like the Met Office, Royal Navy, and BBC World Service. Furthermore, “Greenwich Mean Time” is also the name of a time zone used by some countries in Africa and Western Europe, including Iceland, which uses it year-round.
So, while technically UTC is the primary time standard, in common usage and especially when discussing historical context, GMT is still widely recognized and understood. In many practical situations, especially for general time inquiries, GMT and UTC can be considered interchangeable.
The Origins of Greenwich Mean Time
The ability to accurately measure the relationship between mean (clock) time and solar time became possible with the invention of the pendulum clock in the 1650s.
John Flamsteed, the first Astronomer Royal, played a pivotal role. In the early 1670s, he devised a formula to convert solar time to mean time and published conversion tables. Shortly after, he was appointed Astronomer Royal and established at the newly built Royal Observatory in Greenwich. Equipped with the most advanced pendulum clocks, set to the local time, this marked the inception of Greenwich Mean Time – the average time of the sun’s meridian crossing at Greenwich. Initially, GMT’s significance was primarily confined to the realm of astronomy.
GMT and the Longitude Problem
In the 18th century, Nevil Maskelyne, the fifth Astronomer Royal, broadened the reach of Greenwich Mean Time.
In 1767, Maskelyne introduced the Nautical Almanac, a crucial tool in the 18th-century quest to solve the longitude problem. This almanac contained tables of lunar distance data, derived from Greenwich observations and using GMT as the time standard. This data allowed navigators to determine their position at sea with unprecedented accuracy.
GMT was also fundamental to another solution to the longitude challenge: John Harrison’s marine timekeepers.
British sailors began to carry chronometers set to GMT. This enabled them to calculate their longitude relative to the Greenwich meridian (designated as 0° longitude).
These advancements paved the way for GMT to become the global time standard a century later.
Find out about the longitude problem
Railways and the Rise of GMT as the UK Time Standard
Until the mid-19th century, local solar time prevailed in almost every town. There were no national or international agreements on time measurement. This meant inconsistent timings for the start and end of the day, and even variations in the length of an hour. Alongside Greenwich Mean Time, other local times existed, such as Bristol Mean Time and Cardiff Mean Time, differing from GMT by several minutes.
However, the rapid expansion of railway and communication networks in the 1850s and 1860s made a national time standard indispensable.
British railway companies took the initiative, adopting a single standard time across their networks to simplify timetables. They predominantly used Greenwich Mean Time. In December 1847, the Railway Clearing House officially adopted GMT across Great Britain, recognizing it as “Railway Time.”
By the mid-1850s, most public clocks in Britain were synchronized to Greenwich Mean Time. Finally, in 1880, it became Britain’s legal standard time.
GMT: From UK Standard to International Time
In 1884, the Greenwich Meridian was internationally recognized as the Prime Meridian of the World.
This decision was driven by two primary factors. First, the United States had already adopted Greenwich as the basis for its national time zone system. Second, in the late 19th century, 72% of global commerce relied on sea charts using Greenwich as the Prime Meridian.
The rationale behind this recommendation was that designating Greenwich as Longitude 0º would benefit the largest number of people worldwide.
As the reference point for GMT, the Prime Meridian at Greenwich became the center of world time and the foundation for the global time zone system.
The Airy Transit Circle telescope at the Royal Observatory Greenwich was chosen to define the Prime Meridian of the World. Designed by Astronomer Royal George Biddell Airy, this telescope marked 0° longitude. This meridian line also signified the start of the Universal Day. The crosshairs in the Airy Transit Circle eyepiece precisely mark the meridian line.
Find out more about the Airy Transit Circle
The Shepherd Gate Clock: Public Display of GMT
The Shepherd gate clock, located at the entrance to the Royal Observatory, holds a special place in history. It was the first clock to publicly display Greenwich Mean Time directly. This “slave” clock is connected to the Shepherd master clock, installed at the Royal Observatory in 1852.
From 1852 to 1893, the Shepherd master clock served as the heart of Britain’s time system. Its time was disseminated via telegraph wires to cities across the UK and even internationally, including Harvard University in the USA via transatlantic cable by 1866. It stands as one of the most significant clocks ever created in terms of distributing accurate time into everyday life.
A distinctive feature of the Shepherd gate clock is its 24-hour dial, unlike the more common 12-hour clock face. At 12 noon, the hour hand points downwards instead of upwards. Originally, the clock displayed astronomical time, where the 24-hour day began at noon. In the 20th century, it was modified to show Greenwich Mean Time, with the 24-hour day starting at midnight. It continues to display GMT and does not adjust for British Summer Time.
In conclusion, understanding what time it is in GMT is not just about knowing the current hour in a specific location. It’s about recognizing the legacy of Greenwich Mean Time as a cornerstone of global timekeeping, a system born from scientific inquiry, navigational necessity, and the ever-increasing interconnectedness of our world.
