GPS, UTC, and TAI Clocks

The 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
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
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 TAI is always ahead of GPS by 19 seconds.

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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