Responsibility for the definition of time scales left the astronomical community some 40 years ago when, in 1967, the second became defined by an atomic transition in the International System of units SI and when TAI was defined as the primary international time scale in 1971. Atomic time is now 107 times more stable than the Earth rotation and some 104 times more stable than the planetary orbital motions that were used to define time until 1967.

But time still interacts with astronomy in many ways: as the independent variable for the description of all dynamical systems, its stability allows one to study these systems and their perturbations. Time is therefore of major importance for astronomers, with time scales based on the SI second for practical applications and coordinate time scales for theoretical developments. Precise timing of the rotational and orbital periods of pulsars has the potential to contribute to the long-term stability of International Atomic Time (TAI), thereby returning some aspects of time keeping to astronomy. Furthermore, since observational techniques rely on the measurement of the time of propagation of electromagnetic signals, astronomy provides an important testing ground for relativity.

Although universal time is not used any more to provide the official time, it still reflects the Earth rotation and dictates the leap seconds and hence UTC, the international reference for time and frequency. The future of leap seconds is presently still a subject of debate led by the ITU-R Special Rapporteur Group. In parallel, the knowledge of UT1 is needed for any coordinate transformation between terrestrial and celestial reference systems. Together with the atomic time, UT1 serves precise orbit determination for both space research and Earth studies. The recent measurements of multiple space geodetic techniques, individually or in combination, provide high precision monitoring of LOD and UT1, and allow predictions as needed for real time applications. This improved accuracy on the UT1/LOD measurements also brings a new set of constraints for geophysical models.

The present realizations of the Terrestrial Time TT are the International Atomic Time TAI provided by the BIPM on a monthly basis, and TT(BIPM) based on the reprocessing using all primary frequency standard measurements. TT(BIPM) is presently the best reference to estimate the long-term stability of any other time scale, and in particular the long-term stability of pulsars. Thanks to the recent development of new frequency standards, and to the parallel progress in time scale algorithms and in time transfer techniques, the present atomic time scale stabilities and accuracies has been significantly improved.

Pulsars are incredibly stable clocks with a stability that rivals the best atomic clocks. Many pulsars are members of a binary system, enabling very precise measurement of the gravitational interactions between massive bodies and tests of gravitational theories. Such measurements have already given the most precise verification of Einstein's general relativity in the strong-field case. Future observations will reveal higher-order gravitational perturbations, providing even more stringent tests of gravitational theories. Recent developments of "pulsar timing arrays", in which a large sample of millisecond pulsars are regularly timed, have the potential to establish a time scale which is more stable than the best atomic timescales over long time intervals and hence to investigate the stability of these time scales.

They also are sensitive to errors or omissions in the planetary ephemeredes used to model the Earth's motion and hence to improve those ephemeredes. Finally, they have the potential to make a direct detection of gravitational waves from astronomical sources. Such measurements would open up a new window on the Universe and provide important constraints on models for the early Universe and galaxy evolution.

• UT1/LOD realization and accuracy
• Geophysical impact on UT1
• Short- and long-term variations of UT1
• Use of UT1 for astro-geodetic studies
• UT1 prediction

• Stability of TAI, TT(BIPM)
• Impact of new frequency standards on SI time scales
• GNSS time scales
• Time transfer
• Recent Developments with Leap Seconds

• Techniques of precision pulsar timing
• Pulsar time scales
• Pulsar tests of gravitational theories
• Pulsar Timing Arrays and detection of gravitational waves
• Improving solar-system ephemeredes
• Pulsar Timing Noise

The abstracts must be submitted before March 1st, 2009, via the website of the IAU General Assembly: http://www.astronomy2009.com.br/
sub-menu âÀÜInstructions for PresentersâÀÝ

ƒŠ	ƒŠ9:00-ƒŠ9:30	ƒŠ	Invited	ƒŠ	D. Gambis, C. Bizouard	ƒŠ	Monitoring UT1 from astro-geodetic techniques. State of the art and prospective.
ƒŠ
ƒŠ	ƒŠ9:30-ƒŠ9:45	ƒŠ	ƒŠ	ƒŠ	V. Zharov	ƒŠ	Instability of the celestial reference frame and effect on UT1
ƒŠ
ƒŠ	ƒŠ9:45-10:00	ƒŠ	ƒŠ	ƒŠ	S. Klioner	ƒŠ	On the Relativistic Theory of Earth Rotation
ƒŠ
ƒŠ	10:00-10:15	ƒŠ	ƒŠ	ƒŠ	J. Vondrak , C. Ron , V. Stefka	ƒŠ	New solution of Earth Orientation Parameters in 20th century
ƒŠ
ƒŠ	10:15-10:30	ƒŠ	ƒŠ	ƒŠ	N. Capitaine , P. Wallace	ƒŠ	Implementation of the IAU 2000 definition of UT1 in astronomy
ƒŠ

ƒŠ	11:00-11:30	ƒŠ	Invited	ƒŠ	R. Gross	ƒŠ	Impact of Geophysical Fluids on UT1 Variations
ƒŠ
ƒŠ	11:30-11:45	ƒŠ	ƒŠ	ƒŠ	S. Englich , H. Schuh , R. Weber	ƒŠ	Short-term tidal variations in UT1: compliance between modelling and observation
ƒŠ
ƒŠ	11:45-12:00	ƒŠ	ƒŠ	ƒŠ	H. Schuh , J. Boehm , S. Englich , A. Nothnagel	ƒŠ	Determination of UT1 by VLBI
ƒŠ
ƒŠ	12:00-12:15	ƒŠ	ƒŠ	ƒŠ	A. Brzezinski, N. Capitaine	ƒŠ	Semidiurnal signals in UT1/LOD due to the influence of tidal gravitation on the triaxial structure of the Earth
ƒŠ
ƒŠ	12:15-12:30	ƒŠ	ƒŠ	ƒŠ	W. Wooden , B. Luzum , N. Stamatakos	ƒŠ	Current Status and Future Directions for IERS RS/PC Predictions of UT1
ƒŠ

ƒŠ	14:00-14:15	ƒŠ	ƒŠ	ƒŠ	T. Fukushima	ƒŠ	Time Ephemeris
ƒŠ
ƒŠ	14:15-14:25	ƒŠ	ƒŠ	ƒŠ	D. D. McCarthy	ƒŠ	The Future of the Leap Second
ƒŠ
ƒŠ	14:25-15:30	ƒŠ	ƒŠ	ƒŠ	ƒŠ	ƒŠ	POSTER SESSION
ƒŠ

ƒŠ	16:00-16:25	ƒŠ	Invited	ƒŠ	G. Petit	ƒŠ	Atomic time scales TAI and TT(BIPM): present performances and prospects
ƒŠ
ƒŠ	16:25-16:45	ƒŠ	Invited	ƒŠ	D. Matsakis	ƒŠ	Algorithms for UTC and TT
ƒŠ
ƒŠ	16:45-17:00	ƒŠ	ƒŠ	ƒŠ	P. Uhrich , P. Tuckey	ƒŠ	The use of Galileo signals for time transfer metrology
ƒŠ
ƒŠ	17:00-17:15	ƒŠ	ƒŠ	ƒŠ	E.F. Arias , G. Panfilo	ƒŠ	Impact of new frequency standards on the international time scales
ƒŠ
ƒŠ	17:15-17:30	ƒŠ	ƒŠ	ƒŠ	H. Takiguchi , Y. Koyama , R. Ichikawa , T. Gotoh , A. Ishii , T. Hobiger , M. Hosokawa	ƒŠ	VLBI Measurements for Frequency Transfer
ƒŠ

ƒŠ	ƒŠ9:00-ƒŠ9:30	ƒŠ	Invited	ƒŠ	S. Kopeikin	ƒŠ	Stability of pulsar rotational and orbital periods
ƒŠ
ƒŠ	ƒŠ9:30-ƒŠ9:45	ƒŠ	ƒŠ	ƒŠ	J.O. Urama , A.E. Chukwude	ƒŠ	Large glitches, small glitches and timing noise
ƒŠ
ƒŠ	ƒŠ9:45-10:00	ƒŠ	ƒŠ	ƒŠ	N. Wang	ƒŠ	Pulsar glitches detected at Urumqi Observatory
ƒŠ
ƒŠ	10:00-10:15	ƒŠ	ƒŠ	ƒŠ	A. Rodin	ƒŠ	Pulsar timing array
ƒŠ
ƒŠ	10:15-10:30	ƒŠ	ƒŠ	ƒŠ	M. Pshirkov	ƒŠ	Investigating ultra-long gravitational waves with measurements of pulsars rotational parameters
ƒŠ

ƒŠ	11:00-11:30	ƒŠ	Invited	ƒŠ	M. Kramer	ƒŠ	Binary pulsar tests of gravitational theories
ƒŠ
ƒŠ	11:30-11:45	ƒŠ	ƒŠ	ƒŠ	Y. Ilyasov , V. Zharov , M. Sekido	ƒŠ	Impact of Pulsar Giant Pulses on Distant Clocks Comparison
ƒŠ
ƒŠ	11:45-12:00	ƒŠ	ƒŠ	ƒŠ	R. Manchester	ƒŠ	Detecting Gravitational Waves with Pulsar Timing
ƒŠ
ƒŠ	12:00-12:15	ƒŠ	ƒŠ	ƒŠ	V. Potapov , S. Kopeikin	ƒŠ	Timing of binary pulsars and the search for the low-frequency gravitational waves.
ƒŠ

The instructions for presenters can be found on the IAU website : http://www.astronomy2009.com.br/instrpres.html

The proceedings will be published in
HIGHLIGHTS OF ASTRONOMY, Volume 15
Editor-in-Chief: Ian F Corbett
Publisher: Cambridge University Press (CUP, UK)

The proceedings must be written in Latex. You can find the author's style file as well as a number of sample and âÀØreadmeâÀÙ files to create your paper, on the IAU website, at the following address: http://www.iau.org/static/scientific_meetings/authors_proceedings/

Your contribution should be send to p.defraigne@oma.be by email no later than the September 15, 2009, so that we can assemble all the papers and send the complete volume to the IAU in the deadline. As we receive only a maximum of 30 pages, only summaries can be proposed. These should be of 2 pages for invited talks and 1 page for oral contributions. There is unfortunately no possibility to include a paper for the poster presentations. All Authors are also requested to download the IAU Copyright Form from the IAU website, to complete it and to send it to Pascale Defraigne (see the contact info above), as the Editor of the JD. She will then send the complete set of IAU Copyright Forms, together with the complete manuscript of the JD Proceedings, to the IAU.