Coordinated Universal Time

Coordinated Universal Time (UTC) was previously referred to as Greenwich Mean Time (GMT). It is the mean solar time measured along the prime meridian, which passes through Greenwich, England at zero degrees longitude. This provides a common reference time for all other time zones on the Earth, and simplifies the task of identifying when particular celestial events will occur.

Zero hours UTC occurs at midnight, when the Sun undergoes a lower meridian transit of the prime meridian.

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