• What is UTC or Coordinated Universal Time

    Let’s talk about time standards…

Photo: By TimeZonesBoy – US Central Intelligence Agency

Each country establishes its time zone according to its latitude, longitude and other geopolitical aspects; but, if you are flying a plane, crossing several countries in a few hours, what time zone do you use for communications or navigation?

For this reason, the need arose to create a reference time system, Coordinated Universal Time or UTC, and that is what we are going to talk about in this article.


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When UTC was established?

In October 1884, the International Meridian Conference was held in the United States, where 25 countries met in Washington DC to choose “a meridian to be used as a common zero longitude and standard of time throughout the world”.

Initially, three locations were proposed for reference: the island of El Hierro (Spain), the city of Paris (France) and the Royal Observatory at Greenwich (UK). In the end, the latter was chosen almost unanimously.

Since then, the Greenwich meridian has been considered as the zero meridian, serving as the reference for Coordinated Universal Time or UTC.

What are time zones?

A time zone is the space between each of the meridians into which the Earth’s surface is divided. In total, the Earth is divided into 24 time zones, coinciding with the 24-hour length of a day.

Each time zone covers 15º of circumference, to complete the 360º that a circumference measures, in this case, that of our planet (24 x 15º = 360º).

As you know, the sun rises in the east and sets in the west; therefore, when we move from one time zone to another, towards the east we add hours and, towards the west, we subtract them.

In Spain, the local time in winter is UTC+1 and, in summer, UTC+2. Coordinated Universal Time, or UTC time, never changes; what does change are the times in some countries to adapt to the hours of sunlight.

Travelling back in time on an aeroplane

It is always said that time travel is impossible, but you will see that this is not entirely true. When a plane crosses the Greenwich Mean Greenwich Mean Time heading east, it will go back 24 hours in time, while if it crosses west, it will go forward one day.

In other words, if you take off from New Zealand to Hawaii on 1 January, you will arrive on 31 December… Just in time to celebrate New Year’s Eve again!

However, what sounds like so much fun is not so much fun when it comes to political or economic management. That is why there are some exceptions, such as the Tonga islands in the South Pacific, which have the time zone UTC+13.

What is Zulu time?

Zulu time is the way of designating Greenwich Mean Time in air navigation. That is, in aviation, to know that we are referring to Coordinated Universal Greenwich Mean Time, the etymology ‘Zulu time’ is used.

And why Zulu? Each time zone is assigned a correlative letter; for example, UTC+1 was assigned A (alpha), UTC+2, B (bravo), and so on.

In the case of Greenwich, the letter Z corresponds to it, which, in the radio alphabet, is Zulu. Hence the origin of Zulu time.

However, although Zulu time, UTC and GMT take the same reference, the time at the Greenwich Observatory, you should know that they are not the same.

GMT time

GMT, or Greenwich Mean Time, is defined according to the movements of the Earth with respect to the Sun, and is the time standard that was used before UTC was taken as the new reference standard.

For a long time, the Earth’s rotation and translation around the Sun were the most accurate references for determining time.

But what was the problem? These movements are not constant and, for aerial navigation, as well as for many other fields of science, it is necessary to be governed by a standard time of the highest precision.

Coordinated universal time is derived from International Atomic Time, determined by the 70 or so atomic clocks around the world.

What time do pilot use?

If you’ve paid attention to everything we’ve told you, you probably already know the answer.

Pilots can cross several time zones on the same flight, so to avoid communication problems, confusion and delays, aviation uses Zulu time, which also coincides with UTC.

So, although you will see on your boarding pass the local times of origin and destination, pilots and crew members, as well as flight plans, will all be using Zulu time.

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