While expecting a huge increase of interest in the IAU as a result of the planet definition issue on the agenda of the IAU XXVI General Assembly, Prague, Czech Republic, August 2006, the Executive Committee appointed Lars Lindberg Christensen as Press Officer in June 2006. He will stay on the job till at least the IAU XXVII General Assembly in Rio de Janeiro, Brazil, August 2009.

At the IAU XXVI General Assembly in 2006, the Division I decided to create the Working Group on Astrometry by Small Ground-Based Telescopes (WG-ASGBT). Its scientic goals are to foster the follow-up of small bodies detected by the large surveys including the NEOs; to set-up a dedicated observation network for the follow-up of objects which will be detected by Gaia; to contribute to the observation campaigns of the mutual events of natural satellites, stellar occultations, and binary asteroids; and to encourage teaching astrometry for the next generation. The present report gives the main activities carried out in these areas with small telescopes (diameter less than 2m).

The Program Group for World-wide Development of Astronomy (PG-WWDA) is one of nine Commission 46 program groups engaged with various aspects of astronomical education or development of astronomy education and research in the developing world. In the case of PG-WWDA, its goals are to promote astronomy education and research in the developing world through a variety of activities, including visiting astronomers in developing countries and interacting with them by way of giving encouragement and support.

Two major astronomical experiments are underway at the US Amundsen-Scott South Pole Station. The first is the South Pole Telescope, a 10m sub-millimetre telescope designed to measure primary and secondary anisotropies in the CMBR, with the aim of placing constraints on the equation of state for dark energy. The second is the IceCube neutrino observatory, which will be a cubic kilometre array designed to image sources of high energy neutrinos.

The Historical Instruments Working Group (WG-HI) and Commission 41 started planning an interdisciplinary conference titled Astronomy and its instruments before and after Galileo since January 2007. This conference, as an IYA2009 initiative, aims “to highlight mankind's path toward an improved knowledge of the sky using mathematical and mechanical tools as well as monuments and buildings, giving rise, in doing so, to scientific astronomy”. Commission 46 and Commission 55 also support this conference, to be held on the Isle of San Servolo, Venice (Italy), 27 September – 3 October 2009. As a fact of history, it was in Venice that Galileo was advised and got material (glass) to make his telescope, and in Venice he presented an working instrument to Venetian Doge in August 1609. The conference is co-sponsored by IAU as a Joint Symposium with the INAF – Astronomical Observatory of Padova, Italy.

This was the second Triennium in which the Central Bureau issued electronic-only CBETs to aid in the rapid dissemination of reports. Only 174 CBETs had been issued in the 2002-2005 Triennium, but they evolved into a full supplemental and complemental publication to the Circulars during this past Triennium, reflecting the move toward electronic publication and away from printed publication.

Van Leeuwen has completed and published the new reduction of the Hipparcos data. Parallax accuracies have improved by up to a factor five for the brightest stars and correlations effectively removed.

Commission 36 covers the whole field of the physics of stellar atmospheres. The scientific activity in this large subject has been very intense during the last triennium and led to the publication of a large number of papers, which makes a complete report quite impractical. We have therefore decided to keep the format of the preceding report: first a list of areas of current research, then Web links for obtaining further information.

Division V deals with all aspects of stellar variability, either intrinsic or due to eclipses by its companion in a binary system. In the case of intrinsic stellar variability the analysis of pulsating stars, surface inhomogeneities, stellar activity and oscillations are considered. For close binaries, classical detached eclipsing binaries are studied as well as more interacting systems, like contact and semi-detached binaries, or those with compact components, like cataclysmic variables and X-ray binaries, including the physics of accretion processes.

Commission 49 covers research on the solar wind, shocks and particle acceleration, both transient and steady-state, e.g., corotating, structures within the heliosphere, and the termination shock and boundary of the heliosphere.

The Working Group, created in 1982 during the IAU General Assembly in Patras (Greece), exists to examine, organize, and coordinate the various sets of standard stars for the fields in which they are used: radial velocities, spectral classification, photometry, astrometry, and others. It also provides a forum for discussion and education. All those working with and upon standard stars are considered members of the WG.

The Working Group on Active B-type Stars (formerly known as the Working Group on Be Stars) was re-established under IAU Commission 29 at the IAU General Assembly in Montreal, Quebec (Canada) in 1979, and has been continuously active to the present. Its main goal is to promote and stimulate research and international collaboration on the field of the active early-type (OB) stars.

Commission 53 on Extrasolar Planets was created at the 2006 Prague General Assembly of the IAU, in recognition of the outburst of astronomical progress in the field of extrasolar planet discovery, characterization, and theoretical work that has occurred since the discovery of the pulsar planets in 1992 and the discovery of the first planet in orbit around a solar-type star in 1995. Commission 53 is the logical successor to the IAU Working Group on Extrasolar Planets WG-ESP, which ended its six years of existence in August 2006. The founding president of Commission 53 is Michael Mayor, in honor of his seminal contributions to this new field of astronomy. The vice-president is Alan Boss, the former chair of the WG-ESP, and the members of the Commission 53 Organizing Committee are the other former members of the WG-ESP.

Commission 55 was approved at the IAU XXVI General Assembly in Prague, 2006, following the great success of the Working Group Communicating Astronomy, which had been set up in 2003.

Commission 10 deals with solar activity in all of its forms, ranging from the smallest nanoflares to the largest coronal mass ejections. This report reviews scientific progress over the roughly two-year period ending in the middle of 2008. This has been an exciting time in solar physics, highlighted by the launches of the Hinode and STEREO missions late in 2006. The report is reasonably comprehensive, though it is far from exhaustive. Limited space prevents the inclusion of many significant results. The report is divided into the following sections: Photosphere and chromosphere; Transition region; Corona and coronal heating; Coronal jets; flares; Coronal mass ejection initiation; Global coronal waves and shocks; Coronal dimming; The link between low coronal CME signatures and magnetic clouds; Coronal mass ejections in the heliosphere; and Coronal mass ejections and space weather. Primary authorship is indicated at the beginning of each section.

Commission 33 provides a forum for astronomers studying the structure and dynamics of the Milky Way Galaxy, a unique laboratory for exploring the stellar and gaseous components of galaxies and the processes by which they form and evolve.

The realization and dissemination of the international time scales is the responsibility of the section on Time, Frequency and Gravimetry of the BIPM. Commission 31 supports and coordinates investigations associated with Time definitions, realizations, astronomical data relevant to atomic timekeeping, such as pulsar data. The major developments achieved during the period 2005-2008 in that domain are reported here.

The Commission home page <iau-c35.stsci.edu> is maintained by Claus Leitherer and contains general information on the Commission structure and activities, including links to stellar structure resources that were made available by the owners. The resources contain evolutionary tracks and isochrones from various groups, nuclear reaction, EOS, and opacity data as well as links to main astronomical journals. As a routine activity, the Organizing Committee has commented on and ranked proposals for several IAU sponsored meetings. Our Commission acted as one of the coordinating bodies of a Symposium held at the IAU XXVI General Assembly in Prague, August 2006, (IAU Symposium No. 239 Convection in Astrophysics, and participated in the organization of the following Joint Discussions: JD05 Calibrating the Top of the Stellar Mass-Luminosity Relation, JD06 Neutron Stars and Black Holes in Star Clusters, JD08 Solar and Stellar Activity Cycles, JD11 Pre-Solar Grains as Astrophysical Tools; JD14 Modelling Dense Stellar Systems; and JD17 Highlights of Recent Progress in the Seismology of the Sun and Sun-like Stars.

The tremendous progress in technology which we have witnessed during the last 30 years has led to enormous improvements of observational accuracy in all disciplines of fundamental astronomy. Relativity has been becoming increasingly important for modeling and interpretation of high accuracy astronomical observations during at least these 30 years. It is clear that for current accuracy requirements astronomical problems have to be formulated within the framework of General Relativity Theory. Many high-precision astronomical techniques have already required the application of relativistic effects, which are several orders of magnitude larger than the technical accuracy of observations. In order to interpret the results of such observations, one has to construct involved relativistic models. Many current and planned observational projects can not achieve their goals if relativity is not taken into account properly. The future projects will require the introduction of higher-order relativistic effects. To make the relativistic models consistent with each other for different observational techniques, to formulate them in the simplest possible way for a given accuracy, and to formulate them in a language understandable for astronomers and engineers who have little knowledge of relativity are the challenges of a multidisciplinary research field called Applied Relativity.

The working group is pursuing activities co-organized and/or co-sponsored by UN, ESA, NASA, JAXA, UNESCO, COSPAR, IAU and others for the world-wide development of basic space science.