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The iconic 24-hour Shepherd Gate Clock is located outside the Royal Greenwich Observatory in Greenwich, England. An early example of an electric clock, it displays time in Greenwich Mean Time (GMT) or Zulu Time. Image credit: stocknshares/Getty ImagesThe development of rail, automobile, and eventually air travel — which involves the swift movement of thousands of planes through the skies at any given moment — highlighted the need for a standardized time system to keep all transportation operations synchronized.
Pilots can traverse several time zones in a short span, which is why it's crucial to maintain awareness not just of a plane's location, but also of the exact time it will arrive. To achieve this, they rely on Zulu Time conversions.
The Origins of Zulu Time
A close-up view of the prime meridian line, defined by astronomer James Bradley at the Royal Observatory in Greenwich, England. This line has marked the 0-degree longitude since Bradley established it in 1750. Image credit: Pam Susemiehl/Getty ImagesIn 1960, the International Radio Consultative Committee officially adopted a single universal time for pilots and others to follow as a fixed "time zone," ensuring global consistency.
This time system, called Zulu Time, is recognized as the standard time in Greenwich, England, also known as Greenwich Mean Time (GMT). In 1884, Greenwich was designated as the location of 0 degrees longitude, also known as the prime meridian, which separates the Eastern and Western Hemispheres.
Why Was Greenwich Chosen?
Technically, any city on Earth could have been designated as the starting point for the prime meridian, as it serves simply as a reference for measuring directions both west and east. However, Greenwich, England, was chosen because in 1675, King Charles II established an observatory there to solve the problem of determining a universal reference point for navigation.
In 1884, Britain, still a dominant world power, proposed Greenwich as the location for the prime meridian at an international conference. The proposal was accepted by the other nations, and it was officially established as the standard.
The Origin of the Term 'Zulu'
Zulu Time, officially known as Coordinated Universal Time, was adopted in 1967. As Greenwich is recognized as the 'zero meridian,' military and aviation personnel began referring to this time as 'Zulu,' since the NATO phonetic alphabet assigns the letter 'Z' to 'Zulu,' making it easier for people to communicate clearly when spelling out words over radio or phone calls.
Click here to learn more about the people who use Zulu Time. The icon will rotate depending on the visibility status, making it easy to toggle the display.
Zulu Time is not only used by airline staff and air traffic controllers, but also by meteorologists tracking weather patterns and in various internet and web standards.
When you first set up your computer, it was probably pre-configured to Zulu Time. You might also see codes like 072154Z in weather reports, which indicates the report was made on the seventh day of the month at 21:54 Zulu Time.
Click here to find out how to convert your local time to Zulu Time. The visibility can be toggled with a rotating icon for easy navigation.
The key thing to understand about Zulu Time is that it remains consistent everywhere in the world. You simply have different points along it. Here's how to calculate your own personal version of Z-Time based on your location.
- Convert the time to a 24-hour format, commonly used in the military. For instance, if it's 2 p.m. where you are, simply add 12 hours to the time, resulting in a military time of 1400.
- Then, account for the time difference from GMT in your location. For example, if you're in the Eastern Daylight Time zone, add four hours (since Eastern Time is four hours behind GMT). This gives you a Zulu Time of 1800Z.
Here's another example: Imagine a flight departs Newark at 10:00 a.m. local time and arrives in Los Angeles at 12:30 p.m. local time. The corresponding Zulu Time would be 1400Z for Newark and 1930Z for Los Angeles. This is because Los Angeles is in Pacific Time, which is three hours behind Eastern Time (Newark). Therefore, you add four hours for Newark and seven hours for Los Angeles to convert to Zulu Time or GMT.
The great thing about Zulu Time is that it eliminates the confusion of different time zones. You don't need to worry about a.m. or p.m. either. It may take some time to adjust to converting to Zulu Time from your local time, but there are many helpful apps and calculators available online to assist you.
Zulu Time (GMT) is also known as Zero Time, Z-Time, and the more precise Coordinated Universal Time (UTC). You may wonder why it's not abbreviated as CUT. The reason comes from the French, who suggested TUC for Temps Universel Coordonné (Coordinated Universal Time in French). To avoid favoring either language, the compromise was to use UTC.
