My inspiration to write this particular series of posts was the latest switch from Daylight Saving Time (DST). There were the inevitable posts and soft news arguments and articles about the reasons for DST. I’m not going to write about DST, but it all reminded me of an experience with a certain defense agency—one that defends against missiles—and the importance of Zulu time. We will get to that anecdote once I’ve finished providing an understanding of the historic actions and eventual reasons of why Zulu time was established and how that relates to space operations.
In my last Zulu time post I wrote the British government offered 20,000 pounds to the first inventor who developed “a method for determining the longitude within 56 kilometers.”* Believe it or not, it took a long time for someone to get it right: nearly 45 years!!
The inventor, John Harrison, developed the H4 marine chronometer in 1759—the world’s first truly accurate timepiece. The H4 exceeded specifications: it could help determine the longitude within 1 kilometer (time-wise, this meant it was off by ONLY five seconds)!! Sure, in this world of ultra-precise Global Positioning Satellites (GPS) such an error would be very problematic. But in 1759, there was no such thing as GPS. For more about the H4 marine chronometer, read the wiki and the excellent references it recommends.
How does a timepiece help with determining location? There are many great resources, but start with the Royal Observatory’s “Longitude Problem” post. Summary: Every 15 degrees of longitude east or west of the Prime Meridian represents one hour forwards or back from the Greenwich time (so, 30 degrees=2 hours, 75=5, etc.). A very accurate clock, like H4, synchronized to a fixed location’s time (Greenwich Mean Time), and a navigator’s sun observations to determine the ship’s distance from that fixed location, would render a precise (for those days) ship location. As an aside, navigators were also in aircraft, like the F-4 fighter jet, for the same reasons.
Harrison’s technology was so good, so robust, the H4’s internal design was the basis of for timepieces well into the 20th century. You can still go see the H4 in the National Maritime Museum, Greenwich, Britain.
Interestingly enough, Greenwich is also where another important activity occurred: the dropping of a “time ball.” Every day at 1 PM, since 1833, the Greenwich Observatory (pictured below), drops a ball to allow nearby marine vessels to synchronize their timepieces, their marine chronometers, to retain relative time accuracy (the ball is the red sphere on top of the tower in the picture). Since Britain was an empire then, with a lot of commerce going on between continents, there were a lot of ships dependent on the punctual actions of the Greenwich Observatory (read this wiki if you’re interested in how the observatory kept time). The punctuality and accuracy of the time ball drop created favorable circumstances for the eventual adoption of the Greenwich Mean Time as the international reference standard in 1884 AD (and the Greenwich longitude as the accepted Prime Meridian).
The United States also used time balls to help mariners keep accurate time. In today’s terms, we call that action a clock hack or time hack. Time balls were used by sailors until about the 1920’s, when radio time signals replaced their use. Time hacks continued, with a bigger user pool relying on radio time signals to synchronize equipment, clocks and watches. Radio time signals continue to be broadcasted. If you’ve ever dialed (303) 499-7111, you’ve already heard an example of what part of the radio time signal sounds like, courtesy of the United States National Institute of Technology and Standards (NIST) WWV radio station.
Or if you have the right radio receiver, you can try to listen for it on the channels listed on the web page. However, since you’re probably reading this on a computer, you always have the option of using NIST’s clock synchronization for your computer–just go to their “Internet Time Service” page to find out how. There are so many options for you to find out the accurate time–and to think nearly a hundred years ago, this technology was all still being tested.
Of course, something much better, much more accurate came along: Global Positioning Satellites. Also, we haven’t really talked about Zulu time itself—but next post we will. And, I haven’t forgotten about that anecdote.
*Citation: Graham-Cumming, John, The Geek Atlas: 128 Places Where Science & Technology Come Alive, O Reilly, 2009, Chapter 049, page 185.
- Opinion: How the Prime Meridian Changed the World (news.nationalgeographic.com)
- observatory (mapjd.wordpress.com)
- Greenwich (lumierette.wordpress.com)
- Exploring the Delights of Greenwich (traventure.net)
- Clocks fall back Sunday as Daylight Saving Time ends (myfox8.com)
- Trying to Save Some Daylight With Summer Hours (paradelle.wordpress.com)
- Greenwich Royal Observatory (abbymurphyphotography.wordpress.com)
- Greenwich (seanpaulding.wordpress.com)
- A call to retire DST and drop to time zones (jdd.io)