What is "Zulu" time?
"Zulu" time is that which is more commonly know as "GMT"
(Greenwich Mean Time). Our natural
concept of time is linked to the rotation of the earth and we define the length
of the day as the 24 hours it takes (on average) the earth to spin once on its
As time pieces became more accurate and communication became global, there
needed to be a point from which all other world times were based. Since Great
Britain was the world's foremost maritime power when the concept of latitude and
longitude came to be, the starting point for designating longitude was the
"prime meridian" which is
zero degrees and runs through the Royal Greenwich Observatory, in Greenwich,
When the concept of time zones was introduced,
the "starting" point for calculating the different time zones was
agreed to be the Royal Greenwich Observatory.
Unfortunately the Earth does not rotate at exactly a constant rate. Due to
various scientific reasons and increased accuracy in measuring the earth's
rotation, a new timescale, called Universal Time Coordinated or Coordinated Universal Time (UTC), has been
adopted and replaces the term GMT.
The Navy, as well as civil aviation, uses the letter "Z"
(phonetically "Zulu") to refer to the time at the prime
satellites use Zulu Time or Coordinated Universal Time (UTC) as their time
reference. The satellite images that appear on NOAA's Web sites are stamped in
The Department of the Navy serves as the United States official timekeeper,
with the Master Clock facility at the
Naval Observatory, Washington, D.C.