The Transactions XXVIIA Reports on Astronomy 2006-2009 provides a comprehensive and authoritative review of what has been achieved in astronomy during the years 2006 to 2009. These insightful and up-to-date reviews have been written by the presidents and chairpersons of the IAU scientific bodies: the Divisions, the Commissions, and the Working Groups. Topics covered in this wide-ranging volume include: fundamental astronomy; the Sun and heliosphere; planetary sciences; stars; variable stars; interstellar matter; the Galactic system; galaxies and the Universe; optical and infrared techniques; radio astronomy; space and high-energy astrophysics; and other IAU activities. The reviews have been written at a level suitable for colleagues in the same fields, but will also be useful for students and researchers wishing to gain an overview of astronomical fields beyond their own research area.

Preface; Division I. Fundamental Astronomy Jan Vondrfk; Division II. Sun and Heliosphere Donald B. Melrose; Division III. Planetary Systems Sciences Edward L. G. Bowell; Division IV. Stars Monique Spite; Division V. Variable Stars Alvaro Gim_nez; Division VI. Interstellar Matter Thomas J. Miller; Division VII. Galactic System Ortwin Gerhard; Division VIII. Galaxies and the Universe Sadanori Okamura; Division IX. Optical and Infrared Techniques Andreas Quirrenbach; Division X. Radio Astronomy Ren-Dong Nan; Division XI. Space and High-Energy Astrophysics G8nther Hasinger; Division XII. Union-wide Activities Malcolm G. Smith; EC Service. Press Office Lars Lindberg Christensen; Author index.