This book will bring together experts in the field of astronomical photometry to discuss how their subfields provide the precision and accuracy in astronomical energy flux measurements that are needed to permit tests of astrophysical theories. Differential photometers and photometry, improvements in infrared precision, the improvements in precision and accuracy of CCD photometry, the absolute calibration of flux, the development of the Johnson UBVRI photometric system and other passband systems to measure and precisely classify specific types of stars and astrophysical quantities, and the current capabilities of spectrophotometry, and polarimetry to provide precise and accurate data, will all be discussed in this volume. The discussion of `differential’ or `two-star’ photometers will include those developed for planetary as well as stellar photometry and will range from the Princeton polarizing photometer through the pioneering work of Walraven to the differential photometers designed to measure the ashen light of Venus and to counter the effects of aurorae at high latitude sites; the last to be discussed will be the Rapid Alternate Detection System (RADS) developed at the University of Calgary in the 1980s.

Founded in 1911, the AAVSO boasts over 1200 members and observers and is the world's largest non-profit organization dedicated to variable star observation. This timely book marks the AAVSO's centennial year, presenting an authoritative and accurate history of this important association. Writing in an engaging and accessible style, the authors move chronologically through five eras of the AAVSO, discussing the evolution of its structure and purpose. Throughout the text, the main focus is on the thousands of individuals whose contributions have made the AAVSO's progress possible. Describing a century of interaction between amateur and professional astronomers, the authors celebrate the collaborative relationships that have existed over the years. As the definitive history of the first hundred years of the AAVSO, this text has broad appeal and will be of interest to amateur and professional astronomers, as well as historians and sociologists of science in general.