![]() In 1955 the caesium atomic clock was invented. This provided a form of timekeeping that was both more stable and more convenient than astronomical observations. In 1928, the term Universal Time (UT) was introduced by the International Astronomical Union (IAU) to refer to GMT with the day starting at midnight. Until the 1950s, broadcast time signals were based on UT, and hence on the rotation of the Earth. It persisted much longer elsewhere because it was mentioned at the 1884 conference. In 1884 the Greenwich Meridian was used for two-thirds of all charts and maps as their Prime Meridian. In contrast, astronomical GMT began at mean noon, 12 hours after mean midnight of the same date until 1 January 1925, whereas nautical GMT began at mean noon, 12 hours before mean midnight of the same date, at least until 1805 in the British Navy. It started from 0 hours at mean midnight. This agreed with civil Greenwich Mean Time (GMT), used in Great Britain since 1847. Greenwich Mean Time (GMT) is still the standard time for the Prime Meridian (Zero Longitude) and civil time in UK when Daylight Saving Time is not in use.Īt the 1884 International Meridian Conference held in Washington, DC, USA, local mean solar time at the Royal Observatory, Greenwich in England was chosen to define the Universal Day. All rights reserved.UTC - Universal Time Coordinated What is Coordinated Universal Time?Ĭoordinated Universal Time ( UTC ) replaced Greenwich Mean Time (GMT) as the World Standard for time in 1972. UTC is based on atomic measurements, while GMT is based on Earth's rotation. Click here for information on 24 hour clocks If you're like many radio hobbyists, you will soon add a second clock set to UTC to your collection of radio gear. If you live in the central or eastern United States, and those frequencies aren't usable, you can tune to station CHU, in Ottawa, Ontario, Canada on 3330, 7335 780 kHz, to hear the current UTC time. WWV uses a man's voice to give the time, while WWVH uses a female voice. To hear the latest time in UTC, you can tune to stations WWV, in Fort Collins, Colorado and WWVH, Kauai, Hawaii on 2500, 5000, 1000 kHz to hear the time announced in UTC each minute. Since the date is also UTC, you need to listen at 10:00 p.m. on Saturday, however, you won't hear the program. You do the math, and find that 0400 UTC is equal to 10:00 p.m. Suppose your local time zone is Central standard,Īnd you want to hear a shortwave program scheduled to be broadcast at 0400 UTC Saturday. timezones.Ī major source of confusion when using UTC is that the date also follows UTC. The second table is direct conversion from UTC to U.S.A. The number of hours to subtract from local time zones in North America in order to convert West of the zero meridian to the international date line (which includes all of NorthĪmerica), hours are subtracted from UTC to convert to local time. To convert UTC to local time, you have to add or subtract hours from it. Minute later is 0000 ("zero hundred"), and the start of a new UTC day. The time one minute afterġ259 is 1300 (pronounced "thirteen hundred"). ![]() "1:00 a.m." in UTC is expressedĪs 0100, pronounced "zero one hundred." Fifteen minutes after 0100 is expressedĪs 0115 thirty-eight minutes after 0100 is 0138 (usually pronounced "zero one UTC uses a 24-hour system of time notation. Improvements in accuracy, however, the same principles used in GMT have been carried over Reliable, accurate standard for scientific and navigational purposes. Precise atomic clocks, shortwave time signals, and satellites to ensure that UTC remains a GMT became a world time and date standard because it was usedīy Britain's Royal Navy and merchant fleet during the nineteenth century. Greenwich mean time was based upon the time at the zero degree meridian that crossed All of the times and dates found here at Operators, shortwave listeners, the military, and utility radio services are also big International shortwave broadcasters in their broadcast and program schedules. Times), "universal time," and "world time." Refer to it include "Zulu time" (after the "Z" often used after UTC This was formerly known as Greenwich mean time (GMT). This standard is coordinated universal time, abbreviated UTC. Since radio signals can cross multiple time zones and the internationalĭate line, some worldwide standard for time and date is needed.
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