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Coordinated Time Clocks
Understanding Zulu Time And Coordinated Universal Time
Scientists
Around the World Use The Same Time Clock
When you read weather
forecasts and maps, you may notice a four-digit number followed by the letter
"Z" somewhere at their bottom or top.
This alpha-numeric code is
called Z time, UTC, or GMT.
All three are time standards
in the weather community and keep meteorologists - regardless of where in the
world they forecast from—using the same 24-hour clock, which helps avoid
confusion when tracking weather events between time zones.
Although the three terms are
used interchangeably, there are small
differences in meaning.
GMT Time: Definition
Greenwich
Mean Time (GMT) is the clock time at the Prime Meridian (0º longitude) in
Greenwich, England.
Here, the word
"mean" means "average." It refers to the fact that noon GMT
is the moment on
average each year when the sun is at its highest point in the
sky at the Greenwich meridian.
(Because of Earth's uneven
speed in its elliptical orbit and it's axial tilt, noon GMT isn't always when
the sun crosses the Greenwich meridian.)
History
of GMT. The use of GMT began in 19th century Great Britain when British
mariners would use the time at the Greenwich Meridian and the time at their
ship's position to determine the ship's longitude.
Because the UK was an
advanced maritime nation at the time, other mariners adopted the practice and
it eventually spread worldwide as a standard time convention independent of
location.
The
Problem with GMT. For astronomical purposes, the GMT
day was said to start at noon and run until noon the following day.
This made it easier for
astronomers because they could log their observational data (taken overnight)
under a single calendar date.
But for everyone else, the
GMT day started at midnight.
When
everyone switched to the midnight-based convention in the 1920s and 1930s, this
midnight-based time standard was given the new name of Universal Time to
avoid any confusion.
Since this change, the term
GMT isn't used much anymore, except by those living in the UK and its
Commonwealth countries where it's used to describe local time during the winter
months. (It's analogous to our Standard
Time here in the United States.)
UTC Time: Definition
Coordinated
Universal Time is a modern version of Greenwich Mean Time.
As mentioned above, the
phrase, which refers to GMT as counted from midnight, was coined in the 1930s.
Other than this, one of the
biggest differences between GMT and UTC is that UTC does not observe Daylight
Saving Time.
Backwards
Abbreviation. Ever wonder why the acronym for
Coordinated Universal Time isn't CUT?
Basically, UTC is a
compromise between the English (Coordinated Universal Time) and French phrases
(Temps Universel Coordonné). They use the same official abbreviation in all
languages.
Another name for UTC Time is
"Zulu" or "Z Time."
Zulu Time: Definition
Zulu,
or Z Time is UTC Time, only by a different name.
To understand where the
"z" comes from, consider the world's time zones.
YEach
is expressed as a certain number of hours "ahead of UTC" or
"behind UTC"? (For example, UTC -5 is Eastern Standard Time.)
The
letter "z" refers to the Greenwich time zone, which is zero hours
(UTC + 0). Since the NATO phonetic alphabet ("Alpha"
for A, "Bravo" for B, "Charlie" for C...) word
for z is Zulu, we also call it "Zulu Time."
Tiffany Means is a meteorologist, science writer,
and avid cloud watcher/photographer.
Experience
Tiffany has been finding beauty skyward and
sharing it with others since the age of 5. By twelve, she knew she wanted to pursue
weather professionally—thanks in part to the release of the blockbuster
film Twister. Since those days, Tiffany has interned with the domestic and
international weather departments at CNN, written monthly climate reports for
NOAA’s National
Centers for Environmental Prediction, and participated in a number of science
outreach events (such as the Science Olympiad Competition). She has
personally experienced such weather greats as the Blizzard of 1993, and the floods of Hurricane Francis (2004) and
Ivan (2004).
Education
Tiffany holds a bachelor’s degree in Atmospheric
Science with a concentration in weather forecasting from the University of
North Carolina at Asheville.
Tiffany is a proud member of the American
Meteorological Society (AMS).
Tiffany Means
"Weather affects us all. We check it on a
daily basis, and talk about it with complete strangers...but
it is so much more than 5-day forecasts and small talk! Through my
enthusiasm for and expertise in the weather sciences, I hope to spark your
curiosity about our atmosphere, create an awareness that will keep you weather
ready and safe, and strengthen your environmental responsibility to our
atmosphere, water, and earth."
Contact Tiffany: Tiffany can be reached at aboutweatherexpert@gmail.com with questions, comments,
reprint requests, or suggestions. You can also connect with her via the social
links below.
https://www.thoughtco.com/zulu-time-and-coordinated-universal-time-3444435
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