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UTC refers to Coordinated Universal Time, the international time standard that is within one second of mean solar time at zero degrees longitude or at the prime meridian. UTC is obtained using atomic clocks and it takes into account Earth’s rotation.

Also known as Universal Time Coordinated, UTC is the reference for civil time and time zones. It is maintained by the Bureau International des Poids et Mesures (BIPM) – the International Bureau of Weights and Measures that is based in France. 

Both UTC and Greenwich Mean Time or GMT indicate the same time. However, the time measurement system for UTC is more precise.

Similar to GMT, UTC is not affected by Daylight Saving Time (DST). Unlike GMT, UTC is not a time zone. GMT was the time standard till 1972, the year it was replaced by UTC.

There is no doubting the importance of an international reference time to avoid confusion. The first ice warning sent to Captain Smith of RMS Titanic was from the Captain of French liner La Touraine. However, locations of icebergs were provided in times based on the Greenwich Meridian but the longitudes were in terms of the Paris Meridian. Though this wasn’t the cause for the 1912 sinking of the Titanic in the North Atlantic Ocean, it does highlight the need for a standard reference time and meridian. 

Zulu time is UTC in the 24-hour standard commonly used in aviation and by military forces worldwide. The letter “Z”, “Zulu” phonetically, means “zero hours” offset from the time at the prime meridian or UTC + 0 hours.

Countries or cities to the east of the Greenwich Meridian have local times ahead of UTC. Their local times indicated by UTC plus the hours they are ahead. Conversely, local times of countries to the west are indicated by UTC and subtracting the hours behind.

Even though UTC is the de facto international time standard, both UTC and GMT are still used interchangeably, especially when stating the different time zones.