The definition of UTC was implemented in 1972, principally to accommodate celestial navigation and follows recommendation 460 of the International Radio Consultative Committee (CCIR) in 1970. Since 1972 the use of electronic means to navigate has overtaken celestial navigation. This fact along with increasing public dissatisfaction with the possible disruption to modern electronic communications and navigation systems caused by the insertion of a leap second has called into question the current definition of UTC. An extensive review of the background and issues relating to the leap second can be found in Nelson, et al (2001).

Participants in Commission 29 study various aspects of stellar spectra and the information that can be extracted from spectra. The list of fields of interest of the Organizing Committee members suggest some major current research topics in this area are stellar chemical compositions and surface/envelope phenomena. Some of the topics of this commission have overlap with other commissions, such as Commission 14 (Atomic and Molecular Data), 26 (Double and Multiple Stars), 27 (Variable Stars), 30 (Radial Velocities), 36 (Theory of Stellar Atmospheres), and 37 (Star Clusters and Associations). Many Commission 29 members are also members of these other commissions.

The most intensely discussed and controversial issue in time keeping has been the proposal before the International Telecommunications Union (ITU) to redefine Coordinated Universal Time (UTC) so as to replace leap seconds by leap hours. Should this proposal be adopted, the practice of inserting leap seconds would cease after a specific date. Should the Earth's rotation continue to de-accelerate at its historical rate, the next discontinuity in UTC would be an hour inserted several centuries from now. Advocates of this proposal cite the need to synchronize satellite and other systems, such as GPS, Galileo, and GLONASS, which did not exist and were not envisioned when the current system was adopted. They note that leap second insertions can be and have been incorrectly implemented or accounted for. Such errors have to date had localized impact, but they could cause serious mishaps involving loss of life. For example, some GPS receivers have been known to fail simply because there was no leap second after a long enough interval, other GPS receivers failed because the leap second information was broadcast more than three months in advance, and some commercial software used for internet time-transfer Network Time Protocol (NTP) could either discard all data received after a leap second or interpret it as a frequency change. The ambiguity associated with the extra second could also disrupt financial accounting and certain forms of encryption. Those opposed to the proposal question the need for a change, and also point out the costs of adjusting to the proposed change and its inconvenience to amateur astronomers and others who rely upon astronomical calculations published in advance. Reports have been circulated that the cost of checking and correcting software to accommodate the new definition of UTC would be many millions of dollars for some systems. In October 2005 American Astronomical Society asked the ITU for a year's time to study the issue. This commission has supported the efforts of the IAU's Committee on the Leap Second to make an informed recommendation, and anticipates considerable discussion at the IAU's 26th General Assembly in 2006.

JPL continues to be active in creating ephemerides in support of spacecraft navigation as well as various other functions. Many of the products are available on web sites: (a) “Horizons”, the interactive web site, updated on an hourly basis, is located at http://ssd.jpl.nasa.gov. As of August, 2005, it contains orbital elements and ephemerides for the sun and 9 planets, 150 natural satellites (including the Moon), 291, 655 asteroids, 1631 comets, and 34 Spacecraft. Horizons uses the full precision of the JPL DE405.

(b)JPL's Planetary and Lunar Ephemerides in “export” format are available via FTP from the Internet: ftp://ssd.jpl.nasa.gov/pub/eph/export/ or on a CD-ROM: http://www.willbell.com/software/jpl.htm We advise to read the attached README.

(c)The observational data used in fitting the planetary ephemerides is available at the following web site, updated periodically: http://ssd.jpl.nasa.gov/plan-eph-data/

(d)SPICE Toolkit is a subroutine package for experienced programmers who write their own main driving programs for astrometrical computations. SPICE is available at http://naif.jpl.nasa.gov/. It contains a large library of subroutines useful in reading SPICE format ephemeris files (SPK) and in computing many solar system observation geometry parameters associated with the various JPL solar system missions. Available in Fortran, C, and IDL for most popular computing platforms.

Following the Sydney General Assembly, the membership of C41 stood at 352, of whom, at the time of writing, three are known to have deceased. Since the formation of the Inter-Union Commission for the History of Astronomy (ICHA) prior to the Sydney General Assembly, C41/ICHA has subsequently acted, in effect, as an integrated Commission with a single OC. In this triennium the C41/ICHA OC made strong efforts to clarify and simplify the controversial issue of admitting non-IAU members to the ICHA. After prolonged and active consultation, the OC approved the document “Procedures for Admitting non-IAU members to the ICHA” and the OC Secretary Prof. Clive Ruggles officially presented this document to the history of astronomy community in C41/ICHA Newsletter no. 6. It is subject to ratification by the C41/ICHA Business Meeting in Prague in 2006.

We report the major highlights of variable star research within the past three years. This overview is limited to intrinsically variable stars, because the achievements in variable star research stemming from binarity, or multiplicity in general, is covered by the summary report of Commissions 26 and 42.

The triennial report of Commission V Documentation and Astronomical Data/Documentation et Données Astronomiques covers 2002–2005 activities, and in particular the activities of the five Working Groups: Working Group Astronomical Data; Working Group Designations; Working Group Libraries; Working Group FITS; Working Group Virtual Observatories; and of Task Force for the Preservation and Digitization of Photographic Plates.

Commission 12 covers research on the internal structure and dynamics of the Sun, the “quiet” solar atmosphere, solar radiation and its variability, and the nature of relatively stable magnetic structures like sunspots, faculae and the magnetic network. There is considerable productive overlap with the other Commissions of Division II as investigations move progressively toward the fertile intellectual boundaries between traditional research disciplines. In large part, the solar magnetic field provides the linkage that connects these diverse themes. The same magnetic field that produces the more subtle variations of solar structure and radiative output over the 11 yr activity cycle is also implicated in rapid and often violent phenomena such as flares, coronal mass ejections, prominence eruptions, and episodes of sporadic magnetic reconnection.

The last three years have again brought significant progress in nearly all the research endeavors touched upon by the interests of Commission 12. The underlying causes for this success remain the same: sustained advances in computing capabilities coupled with diverse observations with increasing levels of spatial, temporal and spectral resolution. It is all but impossible to deal with these many advances here in anything except a cursory and selective fashion. Thankfully, the Living Reviews in Solar Physicsacute; has published several extensive reviews over the last two years that deal explicitly with issues relevant to the purview of Commission 12. The reader who is eager for a deeper and more complete understanding of some of these advances is directed to http://www.livingreviews.org for access to these articles.

This document introduces the reports by the Commissions and Working Groups of Division IX.

Commission 36 covers all the physics of stellar atmospheres. The scientific activity in this large field has been very intense during the last triennium and led to the publication of a large number of papers which makes an exhaustive report practically not feasible. As a consequence we decided to keep the format of the preceding report: first a list of areas of current research, then web links for obtaining further information.

During the period 2004 to 2005, the following symposia and colloquia were related to the activities of the commission: The A-Star Puzzle (IAUS224), Massive Star Birth: A Crossroads of Astrophysics (IAUS227), and From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution (IAUS228).

The 2003 report of the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements has appeared in Celestial Mechanics and Dynamical Astronomy(2005)volume 91, part 3–4, pages 203–215. The Working Group continues to maintain and update the information for cartographic coordinates and rotational elements for the Sun, Moon, planets, satellites, asteroids, and comets. A report is published treannually. A web site is maintained at http://extranet.astrogeology.wr.usgs.gov/Projects/WGCCRE with the up-to-date information. It is anticipated that the next report will include updates for Saturn (rotation rate) and all of the Saturnian moons, additions for the newly visited comets and asteroids, and a clarification of the Moon's coordinate systems (the mean Earth/polar axis system needs to be defined more precisely).

This report is a brief summary of some of the major achievements in studies of planets and satellites that have been accomplished during the years 2003–2005. Unlike previous years, we do not attempt to provide a detailed overview of the field but rather choose to highlight aspects which are of particular novelty.

In the last triennium two International Schools for Young Astronomers took place in 2004 and 2005, respectively in Morocco and Mexico.

Significant and specific progress has been made in protecting major astronomical sites during the last three years. A brief summary is given, along with references to some of the efforts by members of Commission 50 to control light pollution and radio-frequency interference.

The Working Group on Communicating Astronomy with the Public is under Division XII - Union-Wide Activities. Formed in early 2004, this Working Group has been very active in establishing itself and promoting its core goals.

As for comets 619 comets received names from July 2002 to June 2005. Of this naming 76 percent are SOHO comets and 11 percent include the name of the LINEAR project. A revision of the guidelines for naming comets has been completed in March 2003. The assistance of the director of CBAT, Daniel W. E. Green, in redrafting these guidelines was much appreciated by the committee.

This report covers the activity period 2002–2005 of the IAU Working Group on Massive Stars

Commission 10 aims at the study of various forms of solar activity, including networks, plages, pores, spots, fibrils, surges, jets, filaments/prominences, coronal loops, flares, coronal mass ejections (CMEs), solar cycle, microflares, nanoflares, coronal heating etc., which are all manifestation of the interplay of magnetic fields and solar plasma. Increasingly important is the study of solar activities as sources of various disturbances in the interplanetary space and near-Earth “space weather”.

Over the past three years a major component of research on the active Sun has involved data from the RHESSI spacecraft. This review starts with an update on current and planned solar observations from spacecraft. The discussion of solar flares gives emphasis to new results from RHESSI, along with updates on other aspects of flares. Recent progress on two theoretical concepts, magnetic reconnection and magnetic helicity is then summarized, followed by discussions of coronal loops and heating, the magnetic carpet and filaments. The final topic discussed is coronal mass ejections and space weather.

The discussions on each topic is relatively brief, and intended as an outline to put the extensive list of references in context.

The review was prepared jointly by the members of the Organizing Committee, and the names of the primary contributors to the various sections are indicated in parentheses.

The commission supported the following IAU symposia and colloquia during the period 2002 to 2005: Dark Matter in Galaxies (IAUS220), Gravitational Lensing Impact on Cosmology (IAUS225); Transit of Venus: New Views of the Solar System and Galaxy (IAUC196); Populations of High-Energy Sources in Galaxies (IAUS230); Scientific Requirements for Extremely Large Telescopes (IAUS232).