GPS, UTC, and TAI Clocks

GPS, UTC, and TAI ClocksThe following are based on your PC clock:

• Local time is the date/time reported by your PC (as seen by your web browser). If your PC clock is accurate to a second then the other time scales displayed above will also be accurate to within one second.

• UTC, Coordinated Universal Time, popularly known as GMT (Greenwich Mean Time), or Zulu time. Local time differs from UTC by the number of hours of your timezone.

• GPS, Global Positioning System time, is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves. GPS time was zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds GPS is now ahead of UTC by

  18 seconds.

• Loran-C, Long Range Navigation time, is an atomic time scale implemented by the atomic clocks in Loran-C chain transmitter sites. Loran time was zero at 0h 1-Jan-1958 and since it is not perturbed by leap seconds it is now ahead of UTC by

  27 seconds.

• TAI, Temps Atomique International, is the international atomic time scale based on a continuous counting of the SI second. TAI is currently ahead of UTC by

  37 seconds. TAI is always ahead of GPS by 19 seconds.

See also: Nixie Tube Leap Second Countdown Clock.

For more information about time scales and leap seconds see:

• Systems of Time Time Service Department, U.S. Naval Observatory, Washington, DC

• A brief history of time scales Steve Allen, UCO/Lick Observatory

• Le temps UTC/TAI Bureau International des Poids et Mesures, BIPM UTC/TAI Time Server

• Leap Seconds Time Service Department, USNO

• Future of Leap Seconds Steve Allen, UCO/Lick Observatory

• Modified Julian Date Frequently Asked Questions, Time Service Department, USNO

• Astronomical Time Keeping Astronomical texts for the layman

• Astronomical Calendars MAA Scholar Project

• Some basic information about the different time scales by Paul Schlyter

• Time Scales, UTC, and Leap Seconds From the Time and Frequency Users Manual

• Astronomical Times Richard Fisher, National Radio Astronomy Observatory

• Loran-C Timing Operations U.S. Naval Observatory, Washington, DC

• Loran-C Times of Coincidence (TOC) calculator

• International Earth Rotation Service (IERS) General Information

• A Few Facts Concerning GMT, UT, and the RGO by Richard B. Langley

• Time and Frequency FAQ Time & Frequency Division, NIST

• Leap Second and UT1-UTC Information Time & Frequency Division, NIST

• Time Scales Time Metrology, National Physics Laboratory (NPL)

• The Leap Second Time Metrology, National Physics Laboratory (NPL)

• Leap seconds: why and how Physikalisch-Technische Bundesanstalt (PTB)

• The Time of Internet Italian Standard Time, Guided Tour to Time Measurement

• The Australian National Time System The Second and International Atomic Time

• What are all those different kinds of time Astronomy Frequently Asked Questions

• Chandra, A Time Tutorial Definitions of various time systems and formulae

• The Times of your Life Solar Time, Julian Days, Sidereal Time

• Tidbits about TIME Archives of timezone.com

• Radio Time Checks Origins and Meaning of GMT/UTC

• 1972 Troubled Times Leap Seconds herold[sic] world-wide cataclysm (huh?)

• Leap Seconds Urban Legend (huh?)

• The Greenwich Meridian in the Space Age Time, Atomic Time, Longitude, etc.

• The world time system New Scientist

• History of the Prime Meridian - Past and Present by Jeremy Paul

• Time Physical fundamentals

• UTC New Years Y2K No leap second here!

• Earth rotation Difference in seconds between a UT1 and a TAI clock

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