Commission 20 has been involved in the discussion on discovery credit rules of solar system objects (mainly concerned with asteroids) in particular with the role played by dynamicists in recovering objects by linking their orbits with previous apparitions. A working group was set up to discuss the issue that was integrated by professional astronomers as well as amateurs. There was some exchange of opinions and conflicting views, but the trend of the majority was to keep the discovery credit for the discoverer whose observations led to the object's principal designation, as expressed in the MPC existing rules (see <cfa-www.harvard.edu/iau/info/HowNamed.html>), considering only exceptionally credit for dynamicists when linkage of different apparitions led to the recovery of a lost object. The precise definition of non-trivial linkage should be worked out, and for the time being, the idea is to keep the existing MPC rules and, if necessary, to improve them, rather than starting a new set of rules.

Commission 21 consists of IAU members and consultants with expertise and interest in the study of the light of the night sky and its various diffuse components, at all accessible electromagnetic frequencies. In cosmic distance scales, the subjects of Commission 21 range from airglow and tropospheric scattering in Earth's atmosphere, through zodiacal light in the solar system, including thermal emission from interplanetary dust, integrated starlight in the Milky Way galaxy, diffuse galactic light due to dust scattering in the galactic diffuse interstellar medium, thermal emissions from interstellar dust and free free emission from ionized interstellar gas, to various diffuse extragalactic background sources, including the cosmologically important cosmic microwave background (CMB). Observations of the diffuse night sky brightness at any frequency typically include signals from several of these sources, and it has been the historic mandate of Commission 21 to foster the necessary collaboration of experts from the different astronomical sub-disciplines involved.

Commission 22 is part of Division III on Planetary System Sciences of the International Astronomical Union. Members of Commission 22 are professional scientists studying bodies in the Solar System smaller than asteroids and comets, and their interactions with planets. The main subjects of interest are meteors, meteoroids, meteoroid streams, interplanetary dust particles, and also zodiacal cloud, meteor trains, meteorites, tektites, etc.

Bioastronomy: Search for Extraterrestrial Life was established as Commission 51 of the IAU in 1982. The objectives of the commission included: the search for planets around other stars; the search for radio transmissions, intentional or unintentional, of extraterrestrial origin; the search for biologically relevant interstellar molecules and the study of their formation processes; detection methods for potential spectroscopic evidence of biological activity; the coordination of efforts in all these areas at the international level and the establishment of collaborative programs with other international scientific societies with related interests. In 2006, Commission 51 was renamed simply Bioastronomy at the IAU General Assembly in Prague, and approved for the next six years, the default extension for an IAU Commission.

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.

The activity of the Minor Planet Center continued generally to increase during the two triennia covered by this report, principally because of the continuing success of the surveys for near-earth objects. Chief among these has been the Lincoln (Laboratory) Near-Earth Asteroid Research Project, or LINEAR, which is credited with the discovery of slightly more than half of all the minor planets that have been numbered, although since 2005 the Catalina Sky Survey and Mount Lemmon Survey in Arizona and the Siding Spring Survey in New South Wales (all three of which, together with the long-lasting Spacewatch Survey, are operated from the University of Arizona) have come to dominate the field. The total number of observations of minor planets in the MPC's files more than doubled from 14.1 million in mid-2002 to 30.9 million in mid-2005, with almost another doubling, to 55.4 million, in mid-2008.

A total of 701 comets received names between July 2005 and June 2008. Comets observed only from the SOHO and STEREO missions, as well as further comets recognized from the long-defunct SOLWIND satellite, accounted for 520 of these names.

The Working Group on Planetary System Nomenclature (WG-PSN) develops, maintains and publishes guidelines for naming natural satellites of planets and surface features on all solar system bodies except Earth. When required the WG approves lists of new nomenclature, with accompanying explanatory notes, based on the established guidelines. Approved names are immediately added into the Gazetteer of Planetary Nomenclature. Objections based on significant, substantive problems may be submitted within a 3-months period, and will be ruled on by Division III.

IAU Division IV organizes astronomers studying the characteristics, interior and atmospheric structure, and evolution of stars of all masses, ages, and chemical compositions.

Although we were happy to welcome over 20 new members at the Prague meeting, Commission 26 is still one of the smallest in the IAU. Notwithstanding its size, it continues to carry on an active and diversified program of activities. Our web site, maintained at the US Naval Observatory, contains further information on the Commission. The site includes links to other relevant sites, to databases and catalogues, an archive of our Information Circulars, a list of upcoming meetings of interest, as well as an extensive bibliography of recently published papers on double and multiple stars. The site can be accessed at <ad.usno.navy.mil/wds/dsl.html#iau>.

The Working Group on Binary and Multiple System Nomenclature was formed within Commission 26 following Special Session 3 held during the 2003 Sydney General Assembly. Its purpose is to create the Washington Multiplicity Catalog, a comprehensive database first introduced at a multi-commission meeting at the IAU XXIV General Assembly in Manchester, 2000. Data are being compiled from the US Naval Observatory visual binary catalogs and supplemented with binary and multiple star information from other sources to include but not limited to spectroscopy, photometry, eclipsing and interacting system, as well as extra-solar planets and substellar companions. The goal being creation of a comprehensive hierarchical database and to reduce confusion from multiple nomenclature schemes used by disparate techniques.

The members of IAU Commission 29 Stellar Spectra are actively engaged in the quantitative analysis of spectra of various types of stars. With large and medium size telescopes equipped with high resolution spectrographs LTE and Non-LTE analysis of spectra of all types stars are being carried out. Spectra of stars in our Galaxy, in globular and open clusters, stars in LMC and SMC and in nearby galaxies are being studied. Accurate chemical composition analysis of various types of stars has been carried out during the past three years. Now the analysis of stellar spectra covers the wavelength range from X-ray region to IR and sub-millimeter range. Recently stellar spectra are being analysed using time-dependent, 3D, hydrodynamical model atmospheres to derive accurate stellar abundances.

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.

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.

This report gives an update of developments (since the last General Assembly at Prague) in the areas that are of relevance to the commission. In addition to numerous papers, a new monograph entitled Stellar Spectral Classification with Richard Gray and Chris Corbally as leading authors will be published by Princeton University Press as part of their Princeton Series in Astrophysics in April 2009. This book is an up-to-date and encyclopedic review of stellar spectral classification across the H-R diagram, including the traditional MK system in the blue-violet, recent extensions into the ultraviolet and infrared, the newly defined L-type and T-type spectral classes, as well as spectral classification of carbon stars, S-type stars, white dwarfs, novae, supernovae and Wolf-Rayet stars.

Our Working Group studies massive, luminous stars, with historical focus on early-type (OB) stars, but extending in recent years to include massive red supergiants that evolve from hot stars. There is also emphasis on the role of massive stars in other branches of astrophysics, particularly regarding starburst galaxies, the first stars, core-collapse gamma-ray bursts, and formation of massive stars.

The main activity of the WG on Abundances in Red Giants has been to propose a JD for the IAU GA in 2009. The increasing evidence for distinct populations within globular clusters is leading to the view that there is a continuum between globular clusters and the smallest of the galaxies. Our JD was designed to investigate this link. However, our JD was incorporated into IAU Symposium No. 266 Star Clusters: Basic Building Blocks throughout Time and Space for the IAU XXVII in Rio de Janeiro, 2009. We will be responsible for organising one session in the Symposium to cover the agenda put forward in our JD proposal.

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.

The diversity of physical phenomena embraced by the study of Chemically Peculiar (CP) stars results in an associated research community with interests that are equally diverse. This fact became once more evident during the CP#Ap Workshop that took place in Vienna (Austria) in September 2007, and which gathered over 80 members of this research community. Besides the excellent scientific outcome of the meeting, during the workshop the community had the opportunity to discuss its organization and plans for the future. Following on those plans, the Working Group has submitted a proposal for a Joint Discussion during the IAU XXVII General Assembly, in Rio de Janeiro, which has meanwhile been accepted. Moreover, through an ApN newsletter forum, the Working Group has compiled requests from the community concerning atomic and related data. These requests have been put together and will be shared with Commission 14.

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.