Zulu, GMT, UCT, UTC, CUT?

[Johnny L.A.]

I grew up with 'zulu time'; the 'baseline' time at the Prime Meridian. Soon after, I learned 'Greenwich Mean Time' (GMT). When I was learning to fly, 'zulu' and 'GMT' were commonly and equally used.

Then I heard Universal Time Coordinated (UTC). I often heart it pronounced 'CUT', for Coordinate Universal Time. And I've heard, on a few occasions, 'UCT' for Universal Coordinated Time.

As far as I'm concerned, I'll continue using GMT as the 'official' term and 'zulu' for the colloqial term.

But which acronym is the 'official' official term for the time at the Prime Meridian?

[Whack-a-Mole]

Well...seems they like to use CUT as it is clever but UTC would seem to be the actual acronym.

I gather that from this: What is Co-ordinated Universal Time (UTC)?

[sciguy]

Originally Posted by Whack-a-Mole

Well...seems they like to use CUT as it is clever but UTC would seem to be the actual acronym.

I gather that from this: What is Co-ordinated Universal Time (UTC)?

Maybe the original/official term wasn't in English, so the acronym came from something like "Universel Temps Coordonné" (French, probably badly translated)?

And why "Zulu"? My initial guess is that each time zone has a letter designation, and time zone "Z" got the phonetic alphabet designation "zulu", but that may be overly simplistic. Are there letters not used, or did they include a couple of those "half off" zones like India (which uses GMT +5:30 for the entire country, instead of half at +5 and half at +6)?

[Whack-a-Mole]

Originally Posted by sciguy

Maybe the original/official term wasn't in English, so the acronym came from something like "Universel Temps Coordonné" (French, probably badly translated)?

I cannot imagine why French or any other language would be a basis for this. GMT has always been in England (Greenwich) so I can't see why any other language would sneak in there but who knows...maybe the French are trying to co-opt GMT.

And why "Zulu"? My initial guess is that each time zone has a letter designation, and time zone "Z" got the phonetic alphabet designation "zulu", but that may be overly simplistic. Are there letters not used, or did they include a couple of those "half off" zones like India (which uses GMT +5:30 for the entire country, instead of half at +5 and half at +6)?

Answer...

There are 25 integer World Time Zones from -12 through 0 (GMT) to +12. Each one is 15° of Longitude as measured East and West from the Prime Meridian of the World at Greenwich, England. Some countries have adopted non-standard time zones, usually 30 minutes offset which have a * designation.

Each Time Zone is measured relative to Greenwich, England. There are both civilian designations which are typically three letter abbreviations (e.g. EST) for most time zones. In addition there are military designations. These use each letter of the alphabet (except 'J') and are known by their phonetic equivalent. E.G. Greenwich Mean Time (civilian) or Z = Zulu (military and aviation).

SOURCE: http://wwp.greenwichmeantime.com/info/timezone.htm

[MikeS]

Originally Posted by sciguy

Maybe the original/official term wasn't in English, so the acronym came from something like "Universel Temps Coordonné" (French, probably badly translated)?

Actually, in French it would be "Temps Universel Coordonné", or TUC. The reason UTC was chosen is a great illustration of how, in Calvin's words, "A good compromise leaves everyone unhappy":

In 1970 the Coordinated Universal Time system was devised by an international advisory group of technical experts within the International Telecommunication Union (ITU). The ITU felt it was best to designate a single abbreviation for use in all languages in order to minimize confusion. Since unanimous agreement could not be achieved on using either the English word order, CUT, or the French word order, TUC, the acronym UTC was chosen as a compromise.

(from here)

[Freddy the Pig]

Originally Posted by Johnny L.A.

But which acronym is the 'official' official term for the time at the Prime Meridian?

Greenwich Mean Time. But, since 1972, GMT has no longer served as the direct basis for world timekeeping.

GMT is based on the rotation of the Earth, which is erratic and is gradually slowing down. Universal Time (UT/UTC) is based on atomic clocks, which are perfectly regular and predictable. Since 1972, Universal Time has been the official worldwide standard.

However, Universal Time has been set so that 00:00:00 approximates mean midnight on the Prime Meridian, and is periodically synchronized to the rotation of the Earth through the addition of "leap seconds". So, in a sense, GMT serves as the indirect basis for UT.

[mks57]

GMT is obsolete, and has been for many years. Universal Time is controlled by the International Bureau of Weights and Measures in France. Civil time is usually based on UTC, plus/minus an offset for the time zone.