British ships of the 19th century

The History of the Greenwich Mean Time

Did you know? The Greenwich Mean Time was first created to help travelers and cargo transporters in finding their longitude across the ocean. Nowadays, we have incredible technology with precise GPS instruments that can localize anything anywhere, thanks to our satellites. But it was an entirely different story when it came to finding your way in the ocean in the 1700s. How did the GMT come to be? Is it still used in 2021? We go over GMT’s history in this complete guide down below.

What’s the longitude problem?

As mentioned in our intro, the transoceanic voyagers had only half of the information they needed to travel: the latitude. With the help of a sun table, they were able to determine the latitude by observing the altitude of the sun at noon. However, finding the longitude was actually impossible, and was the cause of many lost ships and crews in the 1700s.

How did GMT fix the longitude problem?

To solve the longitude problem, travelers needed a common point of reference similar to the sun for the sun table. That being said, in the 1700s, there was no Time Zone system available. The latter was created in 1879 by Sir Sandford Fleming, which allowed astronomers of the time to better understand the position of the Earth around the sun.

A few years later, in 1884, Astronomer Royal George Biddell Airy was working on a big project to create a new timetable system that the whole world could easily use. With the help of many other scientists, he discovered the perfect reference point, which was called the Prime Meridian, or 0° longitude.

The name (GMT) for this revolutionary system was taken from the town where the Prime Meridian was discovered, Greenwich (United Kingdom). Since that day, the Greenwich Mean Time has been used worldwide by not only the people, but also by official entities such as the navy and many telecommunication networks.

Is Greenwich Mean Time still used in 2021?

Not as much as before, since the UTC (Coordinated Universal Time) took over and almost entirely replaced GMT. However, there are still some entities using the Greenwich Mean Time, especially in Britain in the winter. Furthermore, here are some of the main actors still using GMT as their legal time to this day:

  • Met Office
  • Royal Navy
  • BBC World Service
  • US Military

Why did Greenwich Mean Time (GMT) get replaced?

Simply put, the Greenwich Mean Time (GMT) and Coordinated Universal Time (UTC) both give sensibly the same time. Although, where they greatly differ is in their precision, whereas UTC is generally much more precise. To better understand the advantages of using UTC over GMT, here are 3 top facts that explain why UTC is now the commonly used system:

  • Precise Atomic Clocks
    First, the UTC uses extremely precise atomic clocks that always give the exact same result, whereas GMT always has some (very small) variables. Atomic clocks, or sometimes called optical clocks, use a fancy quartz oscillator that is transformed into a certain frequency. This frequency will then be applied to a group of atoms, and depending on the frequency, there will be more or fewer electrons around the atoms, which changes the energy levels. This complex process determines the movement of the atomic clock. Such atomic instruments are actually used by NASA since they need the most precise time stamps they can have for their different operations.
  • Taking into account the Imperfections
    This is another department where UTC is doing a lot better than GMT: the imperfections. Since the Earth is not a perfect sphere and that its rotation around the sun is not a perfect circle, then GMT is not 100% reliable, unfortunately. That’s indeed the case because GMT relies on the position of the sun when it is crossing the Prime Meridian. On the other hand, the atomic clocks used by the UTC are taking into account these imperfections, making it a straightforward choice if you want precise results all year long.
  • Daylight Saving Time
    Finally, you must be aware that some countries change times during the year. They either push a clock forward by 1 hour so darkness falls at a later time, or they do the opposite at a later date during the same year. This change is part of the GMT system, but with UTC, you don’t have to change anything, time is always the same for all countries in every time zone of the world.

Which country still uses GMT in 2021?

Even though GMT got replaced by UTC in most countries, the Greenwich Mean Time is still being used in some places. Here’s a list of the countries still using GMT as their civil time clock:

  • Malaysia
  • Australia
  • United Kingdom
  • Ireland
  • South Africa
  • New Zealand
  • India
  • Pakistan
  • Iceland
  • Greenland
  • Isle of Man

And if you are wondering if it’s important to know what time system the country you are visiting is using, no, it is not that important. The main reason is that the time will still be very similar between GMT and UTC. Moreover, most of our phones, tablets, and smartwatches will put the correct time depending on your geolocation automatically. Therefore, you don’t have to worry about whether or not you are in a country that still uses GMT.

Where is the 0° longitude?

You can easily find the Prime Meridian on Google Maps or any other virtual world map on the web. That being said, if you feel adventurous and that you would like to see the 0° longitude for yourself, then know that you can visit the Greenwich Royal Observatory in Greenwich Town.

Located nearby the observatory, a giant line splits our beautiful planet into 2 hemispheres. Once you’re there, you can do everything your heart truly desires: you can walk over the line, jump across from one hemisphere to the next, and of course, take many fun pictures.

Now that you know why it is called the Greenwich Mean Time and how it was discovered, you will be able to differentiate GMT from UTC adequately. Thanks for reading and stay safe!

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