Relationship between tai and utc time

Time Scales: UT1, UTC, TAI, ET, TT, GPS time

relationship between tai and utc time

Steve Allen's detailed history of the different time scales: sla/leapsecs/ The TAI is decided by calculating a weighted average of the times of atomic clocks in such as tidal friction, time difference between UT and UTC is apt to occur. In fact UTC, as an atomic time, is as uniform as the TAI scale can be, but it is always kept closer than seconds with respect to UT1, This difference is given by time zones and the proper adjustments in summer and winter.

Other time zones are based on UTCe. The leap-second system was introduced at the beginning of What is UNIX time? Thousands of programmers rely on this fact. What is the epoch?

relationship between tai and utc time

Originally it was defined as the beginning of GMT. Unfortunately, it is ambiguous; it can refer to a variety of astronomical time scales.

Arthur David Olson's popular time library uses an epoch of For many years, the UNIX localtime time-display routine didn't support leap seconds. Its displays slipped 1 second away from the correct local time as each leap second passed. Nobody cared; clocks weren't set that accurately anyway. Unfortunately, xntpd, a program that synchronizes clocks using the Network Time Protocol, pandered to those broken localtime libraries, at the expense of reliability. Watch how the xntpd time scale increases as a leap second occurs: It cannot be reliably converted to UTC.

By resetting the clock at each leap second, xntpd extracts a correct UTC display except, of course, during leap seconds from the broken localtime libraries.

UTC to GPS Time Correction

Meanwhile, it produces incorrect results for applications that add and subtract real times. Why not fix it? It's easy enough to fix xntpd. TAI as a time scale is a weighted average of the time kept by over atomic clocks in over 50 national laboratories worldwide.

The clocks are compared using GPS signals and two-way satellite time and frequency transfer.

UTC to GPS Time Correction

Due to the averaging it is far more stable than any clock would be alone see signal averaging for a discussion. The majority of the clocks are caesium clocks; the definition of the SI second is written in terms of caesium. The UTC was officially formalized in by the International Radio Consultative Committee in Recommendationhaving been initiated by several national time laboratories.

The system was adjusted several times until leap seconds were adopted in to simplify future adjustments. A number of proposals have been made to replace UTC with a new system which would eliminate leap seconds but no consensus has yet been reached.

Din Tai Fung in UTC

Leap seconds keep UTC within 0. If high precision is not required, the general term Universal Time UT may be used. The UTC time standard, which is widely used for international timekeeping and as the reference for civil time in most countries, uses the international system SI definition of the second, based on atomic clocks.

Like most time standards, UTC defines a grouping of seconds into minutes, hours, days, months, and years. However, the duration of one mean solar day is slightly longer than 24 hours SI seconds.


The purpose of a leap second is to compensate for this drift, by occasionally scheduling some UTC days with or SI seconds. Specifically, a positive leap second is inserted between second This extra second is displayed on UTC clocks as On clocks that display local time tied to UTC, the leap second may be inserted at the end of some other hour or half-hourdepending on the local time zone. A negative leap second would suppress second However, since the UTC standard was established, negative leap seconds have never been needed.

Because the Earth's rotation speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. The argument revolves around the question: The ITU World Radiocommunication Conference WRCin session in Geneva in Novemberhas decided that further studies are required on the impact and application of a future reference time-scale, including the modification of UTC and suppressing the so-called 'leap second'.

A report will be considered by the World Radiocommunication Conference in

relationship between tai and utc time