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Understanding and Reading UTC or GMT Time

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Definition: The National Oceanographic and Atmospheric Administration (NOAA) and The National Weather Service (NWS) use UTC or Zulu time to post weather forecasts and other information so that universal understanding of the times can be expressed throughout the world. In hurricane reporting, this time method is especially important.

Greenwich Mean Time (GMT) began in the 19th century for use in British maritime navigation. Greenwich, England was established as the Prime Meridian with a longitude of zero. In 1970 the Coordinated Universal Time (UTC) system was devised by an international advisory group of the International Telecommunication Union (ITU). The time system was designed to be universal and worldwide in nature so that there was no confusion. The abbreviation became UTC.

While the UTC time was based on GMT time, there are two one main differences between the two. UTC time is based on midnight while GMT is based on noon. However, since few scientists use GMT time anymore, there is increasingly less problems in time conversions. Use the links below to help you convert UTC time to standards time.

Another difference between UTC and GMT time is that GMT is based on Earth's rotation and celestial measurements, UTC is a based on cesium-beam atomic clocks. The two clocks are rarely more than a second apart as leap seconds are applied to UTC.

Reference
NASA

Also Known As: Zulu Time, GMT Time, or Greenwich Mean Time

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