Atomic Time Scales and Their Applications in Astronomy

I start by general remarks on the background of the recommendations on space-time references which are submitted to you.The need to consider time scales in a relativistic framework appeared more than 20 years age following the progress of atomic time standards. After long discussions, this led the IAU to define, In 1976, time scales which were designated, In 1979, as Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB). But soon afterwards difficulties in the interpretation of the definitions of TDT and TDB arose. It appeared that the source of these difficulties was the lack of a global approach to space-time reference systems. This point of view, first voiced by J. Lieske, gained acceptance. At the very beginning of the work of the WGRS Sub-Groups on Frames and Origins (SGFO) and on Time (SGT), It became clear the the primary mission of the SGFO and SGT was to jointly prepare general recommendations on space-time references on which they could base their specific recommendations.

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Astronomical Units, Constants and Time-Scales

Highlights of Astronomy ◽

10.1017/s1539299600001945 ◽

1974 ◽

Vol 3 ◽

pp. 229-232

Author(s):

G. A. Wilkins

Keyword(s):

Time Scales ◽

Working Group ◽

Wide Spectrum ◽

The Other ◽

Astronomical Unit ◽

Conversion Factors ◽

Astronomical Data ◽

The Road ◽

Unit Of Length ◽

Atomic Time

As I have already reported (Trans. IAU XVA, 9, 1973), the Working Group on Units and Time-scales was not able to reach any firm conclusions on whether the concepts of the astronomical unit and ephemeris time should be retained or replaced by the SI unit of length (metre) and atomic time. This disagreement was not unexpected as the membership was deliberately chosen to cover a wide spectrum of opinion. The following comments and suggestions represent a middle-of-the-road approach that is intended to meet the requirements of most astronomers and others who use the astronomical data. It has been suggested to me that this approach is not appropriate for use in those precise applications where relativistic concepts are necessary, and that therefore we should abandon completely the use of astronomical units of mass, length and time. There are, however, many applications where Newtonian concepts are perfectly adequate, and astronomical units are widely in use because of their general suitability and convenience. We should therefore continue to define a system of astronomical units, but should state quite clearly their relationships to SI units. An individual may use either system according to the circumstances, and standard conversion factors will be available for use by those who prefer the other system.

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Atomic Time Scales

IEEE Transactions on Instrumentation and Measurement ◽

10.1109/tim.1972.4314053 ◽

1972 ◽

Vol 21 (4) ◽

pp. 396-400 ◽

Cited By ~ 8

Author(s):

Bernard Guinot ◽

Michel Granveaud

Keyword(s):

Time Scales ◽

Atomic Time

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Atomic Time Scales

Metrologia ◽

10.1088/0026-1394/7/4/003 ◽

1971 ◽

Vol 7 (4) ◽

pp. 146-153 ◽

Cited By ~ 9

Author(s):

A G Mungall

Keyword(s):

Time Scales ◽

Atomic Time

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Long term stability of atomic time scales

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314005444 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 209-210

Author(s):

G. Petit ◽

F. Arias

Keyword(s):

Time Scales ◽

Time Scale ◽

Time Transfer ◽

Long Term Stability ◽

Relative Value ◽

The Stability ◽

Primary Standards ◽

Stability And Accuracy ◽

Atomic Time

AbstractWe review the stability and accuracy achieved by the reference atomic time scales TAI and TT(BIPM). We show that they presently are in the low 10−16 in relative value, based on the performance of primary standards, of the ensemble time scale and of the time transfer techniques. We consider how the 1 × 10−16 value could be reached or superseded and which are the present limitations to attain this goal.

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Fundamental Precision of Pulsar Timing

International Astronomical Union Colloquium ◽

10.1017/s0252921100041087 ◽

1996 ◽

Vol 160 ◽

pp. 83-86

Author(s):

Roger S. Foster

Keyword(s):

Energy Density ◽

Time Scales ◽

Rotational Period ◽

Millisecond Pulsar ◽

Arrival Times ◽

Stochastic Background ◽

Pulsar Timing ◽

Pulsar Timing Array ◽

Pulse Arrival ◽

Atomic Time

Although 13 years have passed since the first millisecond pulsar (MSP) was discovered (Backeret al. 1983), it still has the shortest known rotational period (1.56 ms). MSPs are nature’s most stable clocks (Taylor 1991), with timing stabilities that rival atomic clocks on time scales beyond six months (Matsakis & Foster 1996). Specifically, the instantaneous measurement of the period of the original MSP is determined to a precision of ~ 20 attoseconds (10−18s). With such precision, we are able to predict the pulsar pulse arrival times to a small fraction of the rotational period years into the future. MSPs are powerful sources for use in fundamental astrometry and time keeping applications. Collectively, a population of MSPs distributed around the sky can be used to establish a nearly inertial space-time reference frame (e.g. Foster & Backer 1990). Such a pulsar timing array (PTA) could be used to study drifts in Earth based atomic time scales, perturbation in the planetary ephemerides, relativistic corrections in the solar gravitational potential, and limit the energy density of a stochastic background of gravitational waves from the early universe.

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