TDB differs from TT only in periodic terms.

TCB differs from TT in rate and other mostly periodic terms.

ΔT, Delta T, delta-T, deltaT, or DT is the time difference obtained by subtracting Universal Time ( UT ) from Terrestrial Time ( TT ): ΔT = TT − UT.

Using the water taxi people can travel from Port of Spain to San Fernando which cost TT $ 15. 00 one way and TT $ 30. 00 return.

Terrestrial Time ( TT ) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of the Earth.

For example, the Astronomical Almanac uses TT for its tables of positions ( ephemerides ) of the Sun, Moon and planets as seen from the Earth.

TT is distinct from the time scale often used as a basis for civil purposes, Coordinated Universal Time ( UTC ).

* TT also runs in parallel with the GPS time scale, which has a constant difference from atomic time ( ( TAI-GPS time )

Time coordinates on the TT and TCG scales are conventionally specified using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth.

They are published in the form of table of differences from TT ( TAI ).

As defined, TCB ( as observed from the Earth's surface ) is of divergent rate relative to all of ET, T < sub > eph </ sub > and TDT / TT ; and the same is true, to a lesser extent, of TCG.

TDT is tied in its rate to the SI second, as is International Atomic Time ( TAI ), but because TAI was somewhat arbitrarily defined at its inception in 1958 to be initially equal to a refined version of UT, TT is offset from TAI, by a constant 32. 184 seconds.

* 1977: The British Grand Prix moves from the Isle of Man TT to the British mainland.

Ossa would win four Grand Prix races with the monocoque bike before their rider was killed during the 1970 Isle of Man TT, causing the Ossa factory to withdraw from Grand Prix competition.

Gibb donated all of his share of the money from this concert to the children's ward at Noble's Hospital, Isle of Man, and invited all emergency service staff and marshals for the TT to attend for free.

Most Atari ST ( Mega STE model ), and Atari TT framebuffers were created for the VME rear connector slot of Atari machines dedicated to video expansion cards: Leonardo 24-bit VME graphics adapter, CrazyDots II 24-bit VME graphics card, Spektrum TC graphics card, NOVA ET4000 VME SVGA graphics card ( capable of resolutions up to 1024x768 at 256 colors or 800x600 at 32768 colors ), whose design came from the ISA / PC world ( it was effectively an ATI Mach32 S: with 1 MB of video RAM ).

In addition, an epoch optionally prefixed by " J " and designated as a year with decimals ( 2000 + x ), where x is positive or negative and quoted to 1 or 2 decimal places, has come to mean a date that is an interval of x Julian years of 365. 25 days away from the epoch J2000 = JD 2451545. 0 ( TT ), still corresponding ( in spite of the use of the prefix " J " or word " Julian ") to the Gregorian calendar date of 2000 Jan 1 at 12h TT ( about 64 seconds before noon UTC on the same calendar day ).

We run through the logfile ( from the beginning or the last checkpoint ) and add all transactions for which we encounter Begin Transaction entries to the TT.

Bradley Wiggins of the Garmin Slipstream team used an elliptical chainring from Osymetric in his TT bike ( Felt DA ) in the 2009 Tour de France.

Both wet and dry types of F. tularensis ( identified by the codes TT and ZZ ) were examined during the " Red Cloud " tests, which took place from November 1966 to February 1967 in the Tanana Valley, Alaska.

Mitsubishi and some Audi models ( Audi TT ), meanwhile do not have the M, and instead have the + and -, which is separated from the rest of the shift modes ; the same is true for some Peugeot products like Peugeot 206.

The instant that the gravitational correction started to be applied serves as the epoch for Barycentric Coordinate Time ( TCB ), Geocentric Coordinate Time ( TCG ), and Terrestrial Time ( TT ).

Difficulties were recognized, which led to these being in turn superseded in the 1990s by time scales Terrestrial Time ( TT ), Geocentric Coordinate Time GCT ( TCG ) and Barycentric Coordinate Time BCT ( TCB ).

TT was formally defined in terms of Geocentric Coordinate Time ( TCG ), defined by the IAU on the same occasion.

where TT and TCG are linear counts of SI seconds in Terrestrial Time and Geocentric Coordinate Time respectively, L < sub > G </ sub > is the constant difference in the rates of the two time scales, and E is a constant to resolve the epochs ( see below ).

The present definition of TT is a linear scaling of Geocentric Coordinate Time ( TCG ), which is the proper time of a notional observer who is infinitely far away ( so not affected by gravitational time dilation ) and at rest relative to the Earth.

TDB is now ( since 2006 ) defined as a linear scaling of Barycentric Coordinate Time ( TCB ), and a feature that distinguishes TDB from TCB is that TDB, when observed from the Earth's surface, has a difference from Terrestrial Time ( TT ) that is about as small as can be practically arranged with consistent definition: the differences are mainly periodic, and overall will remain at less than 2 milliseconds for several millennia.

Doing so does not create another version of TAI ; it is instead considered to be creating a better realisation of Terrestrial Time ( TT ).

While TT is strictly uniform ( being based on the SI second, every second is the same as every other second ), it is in practice realised by International Atomic Time ( TAI ) with an accuracy of about 1: 10 < small >< sup > 14 </ sup ></ small >.

For practical purposes the length of the ephemeris second can be taken as equal to the length of the second of Barycentric Dynamical Time ( TDB ) or Terrestrial Time ( TT ) or its predecessor TDT.

The difference between Terrestrial Time ( TT ) ( the successor to ephemeris time ) and atomic time was later defined as follows:

where N is an integer, starting with 0 for the first new moon in the year 2000, and that is incremented by 1 for each successive synodic month ; and the result d is the number of days ( and fractions ) since 2000-01-01 00: 00: 00 reckoned in the time scale known as Terrestrial Time ( TT ) used in ephemerides.

In this role, TT continues Terrestrial Dynamical Time ( TDT ), which in turn succeeded ephemeris time ( ET ).

TT indirectly underlies UTC, via International Atomic Time ( TAI ).

* To millisecond accuracy, TT runs parallel to the atomic timescale ( International Atomic Time, TAI ) maintained by the BIPM.

* TT is in effect a continuation of ( but is more precisely uniform than ) the former Ephemeris Time ( ET ).

TT was defined to be a linear scaling of TCG, such that the unit of TT is the SI second on the geoid ( Earth surface at mean sea level ).

This left the exact ratio between TT time and TCG time as something to be determined by experiment.

In 2000, the IAU very slightly altered the definition of TT by adopting an exact value for the ratio between TT and TCG time, as 1 − 6. 969290134 × 10 < sup >− 10 </ sup >.

( As measured on the geoid surface, the rate of TCG is very slightly faster than that of TT, see below, Relativistic relationships of TT.

: TT = ( 1 − L < sub > G </ sub >) TCG + E

The equation linking TT and TCG is more commonly seen in the form

: TT = TCG − L < sub > G </ sub > × ( JD < sub > TCG </ sub > − 2443 144. 500 3725 ) × 86 400

For continuity with their predecessor Ephemeris Time ( ET ), TT and TCG were set to match ET at around Julian Date 2443 144. 5 ( 1977-01-01T00Z ).

More precisely, it was defined that TT instant 1977-01-01T00: 00: 32. 184 exactly and TCG instant 1977-01-01T00: 00: 32. 184 exactly correspond to the International Atomic Time ( TAI ) instant 1977-01-01T00: 00: 00. 000 exactly.

TT and TCG expressed as Julian Dates can be related precisely and most simply by the equation

TCG is linearly related to TT as: TCG-TT = < var > L < sub > G </ sub ></ var > * ( JD-2443144. 5 ) * 86400 seconds, with the scale difference < var > L < sub > G </ sub ></ var > defined as 6. 969290134e-10 exactly.

Because of the linear relationship between Terrestrial Time ( TT ) and TCG, the same clocks that realise TT also serve for TCG.