I spend a lot of time on webinars around the world, admittedly usually in the US, and the attendance on these is absolutely time-dependent, so when I used to register for a webinar that was scheduled for US time, I did sometimes struggle to do the conversion, especially when some of the time zones have their own little foibles – clocks going forwards or backwards on specific dates combined with our own confusing system of GMT and BST.

Now a lot of times are being quoted in UTC, which makes life a whole lot easier, but if you ever wondered what UTC was here is a potted explanation:

UTC – The World’s Time Standard

Coordinated Universal Time (UTC) is the basis for civil time today. This 24-hour time standard is kept using highly precise atomic clocks combined with the Earth’s rotation.

UTC is the time standard commonly used across the world. The world’s timing centres have agreed to keep their time scales closely synchronized – or coordinated – therefore the name Coordinated Universal Time.

Two components are used to determine UTC:

  • International Atomic Time(TAI): A time scale that combines the output of some 200 highly precise atomic clocks worldwide, and provides the exact speed for our clocks to tick.
  • Universal Time(UT1), also known as astronomical time or solar time, refers to the Earth’s rotation. It is used to compare the pace provided by TAI with the actual length of a day on Earth.

Universal Time (UT) was created at the Washington Meridian Conference in 1884. This is the basis for the 24-hour time zone system we know today.

At the time, Greenwich Mean Time (GMT) was chosen as the world’s time standard. The reference line or starting point, the Prime Meridian, was determined to be the transit circle at the Royal Observatory in Greenwich, London. The transit circle is a part of the telescope’s mechanics and it is still cited as the Prime Meridian’s original reference.

In 1960, the International Radio Consultative Committee formalised the concept of UTC, and it was put into practice the year after. The name Coordinated Universal Time was officially adopted in 1967.

Why UTC – not CUT or TUC?

The official abbreviation for Coordinated Universal Time is UTC. It came about as a compromise between English and French speakers.

  • Coordinated Universal Timein English would normally be abbreviated CUT.
  • Temps Universel Coordonnéin French would normally be abbreviated TUC.

The International Telecommunication Union (ITU) and the International Astronomical Union wished to minimise confusion and designated one single abbreviation for use in all languages.

UTC does not favour any particular language. In addition, the advantage of choosing UTC is that it is consistent with the abbreviation for Universal Time, which is UT, with the variations UT0 and UT1.

UTC was adjusted several times until 1972, when leap seconds were introduced to keep UTC in line with the Earth’s rotation, which is not entirely even, and less exact than atomic clocks.

Until 1972, Greenwich Mean Time (also known as Zulu time) was the same as Universal Time (UT).

Since then, GMT is no longer a time standard. Today, Greenwich Mean Time is only the name of a time zone that is used by a few countries in Africa and Western Europe, including the UK during winter and all year in Iceland

However there are moves afoot to scrap GMT and move to towards CET (Central European Time) for the UK.

So when someone asks you the time you need to ask them if its UTC, GMT, BST or CET  they are after. Then consult your Apple Watch – at least Siri should have all the answers!