World Time Z–Zulu Time, that is–Part 3

Z Clock

Zulu time is Z-time.  It’s really that simple.  It means zero hours, describing the offset of time from the Greenwich Mean Time longitude line.  Why Zulu and not Zero or Z?  It has to do with the alphabet and clear communications.  It has to do with the International Civil Aviation Organization’s (ICAO) needs and that need was clarity in critical communications.

In order to minimize mistakes in communications, the ICAO developed the phonetic alphabet.  If you’re an English speaker, you’re familiar with the basics of this alphabet.  All you have to do is say the letters a little bit differently.  So instead of pronouncing a letter like “S” as just “ess,” you’d verbally relay it as “Sierra.”  “F” would be relayed as “Foxtrot,” and of course “Z” would be “Zulu.”  Mystery solved!!

Such an alphabet made communications easier in international settings to enhance communications for cooperation, so groups like the North Atlantic Treaty Organization (NATO) adopted the ICAO phonetic alphabet.  In fact, NATO developed a publication, the Allied Tactical Publication (ATP)-1, Volume II: Allied Maritime Signal and Maneuvering Book, which lists the phonetic alphabet and explains how to use it.  There are even pronunciation guides for the phonetic alphabet, since not everyone using it is a native English speaker.  Especially those people living in the southern states.

The US military is a part of NATO, so little wonder the military services in the United States use the phonetic alphabet to this day.  It’s not that local time isn’t used by the military services for day to day for things like meetings, lunch, and physical training.  Local time is always there, but when it comes to missions, Zulu time is the expectation, not the exception.  Zulu time could mean the difference between life and death when the military is conducting operations.  If each service used a different standard of time while conducting cooperative operations, things would get very interesting indeed.

The global nature of satellites has promoted the use of Zulu time in space operations and not just in the military space operations.  Whether commercial, government, or military, it doesn’t make sense for satellites to reflect whatever local time zone they may be flying over.  The satellites fly over the time zones too quickly (within minutes for some satellites—and yes, I know geosynchronous satellites are pretty much over the same spot on the earth).   Ground stations for satellites also use Zulu as a common time reference, no matter if they’re located in Antarctica, Guam, or Virginia.  Using Zulu helps to keep things simple.  And that may be the best reason to use Zulu time.

So, as learned from the previous two Zulu posts, we have two common, universally accepted reference points.  The Prime Meridian, is still, more or less, the accepted longitude reference, even for satellites (the International Earth Rotation and Reference Systems Service most recently puts it about 102.5 meters east of the Royal Observatory in Greenwich).  And time is still based off of that longitude as Coordinated Universal Time (UTC) or Greenwich Mean Time (GMT).  Plus, now you know Zulu time is pretty much synonymous with UTC and GMT, as well as Zulu time zone’s relationship to space operations.

From mariners to space operators, ships to satellites, Zulu time has been a standard for knowing where things are, coordinating actions, and keeping things simple.  It’s just such a pervasive, useful, small-seeming thing.  Which leads to the anecdote I’ve been wanting to tell you.

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